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Filtration control is important to ensure safe and high efficient drilling. The aim of the current research is to explore the feasibility of using basil seed powders (BSPs) to reduce filtration loss in water-based drilling fluid. The effect of BSP concentration, thermal aging temperature, inorganic salts (NaCl and CaCl2) on the filtration properties of bentonite/basil suspensions was investigated. The filtration control mechanism of BSP was probed via water absorbency test, zeta potential measurement, particle size distribution measurement, and filter cake morphologies observation by scanning electron microscope. The incorporation of BSPs into the bentonite suspension generated acceptable rheology below 1.0 w/v%. The BSPs exhibited effective filtration control after thermal aging at 120 °C, but less efficiency at 150 °C. After thermal aging at 120 °C, the bentonite suspension containing 1.0 w/v% BSPs could resist NaCl and CaCl2 pollution of 5.0 w/v% and 0.3 w/v% respectively. Besides general filtration control behaviors, the exceptional water retaining capability formed by numerous nanoscale 3D networks in the basil seed gum and considerable insoluble small particles in BSPs might further contribute to the filtration control. The excellent filtration properties bring basil seed a suitable and green candidate for the establishment of high-performance drilling fluids.

Basil seed, containing anionic heteropolysaccharides in its outer pericarp, swells as gelatinous hydrocolloid when soaked in water. In this study, basil seed powder (BSP) was used as a multifunctional additive for water-based drilling fluids. The chemical composition, water absorbency, rheological properties of aqueous suspension of BSP were tested. The effect of BSP on the rheological and filtration of bentonite-based drilling fluid before and after thermal aging was investigated. The inhibition characteristics were evaluated by linear swelling, shale cuttings dispersion and shale immersion test. Lubricity improvement by BSP was measured with extreme pressure lubricity test. The results revealed that incorporation of BSP into bentonite suspension improved rheological and filtration properties effectively after thermal aging of 120 °C. BSP exhibited superior inhibitive capacity to xanthan and synergistic effect with KCl. BSP could reduce friction by forming hydration layer. The nanoscale three-dimensional network structures enable BSP to maintain high water retention and absorb strongly on bentonite and metal surface, contributing to enhanced rheology, filtration, inhibition and lubrication properties. The versatile characteristic of BSP, as well as biodegradation makes it a promising additive using in high performance water-based drilling fluid and a potential alternative to conventional synthetic polymers.

Summary Pore throat blockage due to fines migration during drilling and completion is one of the leading causes of damage to unconsolidated sandstone reservoirs. Therefore, it is necessary to explore an effective control method for fines migration. Five types of nanoparticles in suspension with aqueous NaCl solutions of six different ionic strengths were chosen. Their ability to control the migration of quartz and kaolinite fines in quartz sand as the porous medium is discussed in this work. Results show that nanoparticles can effectively adsorb and fix fines, thus successfully suppressing their migration. Among these nanoparticles, Al2O3 showed the best performance, and nanoparticle suspensions with higher ionic strengths were preferable. A surface element integration method was used to establish a mathematical model for calculating the interaction energy between the formation fines and the rock pore surface with adsorbed nanoparticles. Through atomic force microscopy and zeta potential measurements, the effect of nanoparticle adsorption on the heterogeneity of the pore surface was analyzed in terms of roughness and electrical properties. The interaction energy between the formation fines and the heterogeneous pore surface was calculated; it revealed the microscopic mechanism of how nanoparticles control fines migration. The results indicated that the nanoparticles form an adsorption layer, which enhances the physical and chemical heterogeneities of the pore surface and provides favorable conditions for the adsorption and fixation of fines. As a result, the interaction energy curves of the fines and the pore surface shift downward, and their repulsive barriers decrease or even disappear, exhibiting higher attractive potential energy. These variations promote adsorption and fixation of fines at the pore surface, as confirmed by the experimental results reported in this work, thus successfully preventing formation damage.

With the depletion of the conventional shallow oil/gas reservoirs and the increasing demand for oil and gas, deep drilling become more and more essential to extract the oil/gas from deep formations. However, deep drilling faces many complex challenges. One of the complexities is the degradation of polymers and flocculation of bentonite particles, leading to hardly control the rheological and filtration properties of water-based drilling fluids, especially under ultra-high temperature and high pressure (HTHP) conditions. Therefore, an experimental investigation is performed to study how bentonite-hydrothermal carbon nanocomposites will influence the rheological and filtration properties of water-based drilling fluids under ultra-HTHP conditions. Bentonite-hydrothermal carbon nanocomposites are proposed as non-polymer additives to solve the ultra-HTHP challenge in water-based drilling fluid. The nanocomposites are synthesized by facile hydrothermal reaction, in which biomass starch and sodium bentonite are used as the precursor and template, respectively. In this study, the effect of the nanocomposites on the rheology and filtration properties of water-based drilling fluid are investigated before and after hot rolling at 220 °C and 240 °C. The structure characterization indicates that carbon nanospheres can successfully deposit on the bentonite surface after hydrothermal reaction and finally form as nanocomposites. The elemental carbon content, zeta potential and particle size distribution of the nanocomposites could be adjusted according to the reaction conditions. After thermal aging at 220 °C and 240 °C, addition of nanocomposites can improve the rheological properties significantly where a stable and minor change of rheological properties is observed, which is desirable for ultra-HTHP drilling. Regarding filtration control, after adding 1.0 wt% nanocomposite materials, the filtration loss is reduced by 41% and 44% respectively after aging at 220 °C and 240 °C, which is better than the conventional natural materials that lose their function in this case. The identification of microstructure shows that the hydrothermal reaction endows nanocomposites with a unique surface morphology and an improved surface charge density. The interaction between nanocomposites and bentonite particles forms a rigid connection network, which is the main mechanism to facilitate effective rheology and filtration control under ultra-HTHP conditions. The green and facile synthetic routes and environmentally friendly features of the nanocomposites, coupled with the excellent performance in ultra-HTHP rheology and filtration control, indicate that the nanocomposites have a high promise for water-based drilling fluid in ultra-HTHP drilling. Moreover, it provides a new way to design high performance additives with high temperature stability.

Invert emulsion fluids stabilized by organoclays are important for applications in thixotropic fluids and petrochemical industry, especially in the field of oil extraction. Among these applications, improvement of the rheological properties of invert emulsion fluids at high temperatures lacks detailed study. In the current work, three different organoclays, including organo-sepiolite (OSEP), organo-hectorite (OSHCA) and organo-montmorillonite (OMMT) were prepared through chemical modification of unmodified clays using DODMAC. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that DODMAC is not only adsorbed on the surface of particles, but also inserted into the layers of OMMT and OSHCA. For OSEP particles, DODMAC can only be adsorbed on the surface of particles. Interestingly, the results of optical microscopy and rheology indicate that the OSHCA particle-stabilized invert emulsion fluid provides better rheological properties than the other two organoclays at high temperature. Such high rheological properties is ascribed to the weak flocculation of OSHCA particles. Due to its nonreactive Mg−OH surface groups, OSHCA maintains the rheology of high-temperature aged invert emulsions by reconstructing weak flocculation structure. On the other hand, on the particle surface of OMMT and OSEP, Al−OH may react with OH− under alkaline conditions, which will destroy the weak flocculation due to increased repulsion interaction. These results clearly shed light on the relationship between the performance of invert emulsion at high aged temperature and particle weak flocculation, and also are beneficial to the applications which need stable emulsion at high temperature.

In recent years, developing high-performance shale inhibitors with excellent shale swelling and dispersion inhibition properties has attracted great interests in the drilling industry. 1-Octyl-3-methylimidazolium bromide (OMB), a common imidazolium-based ionic liquid, was introduced as a promising shale inhibitor. Shale hydration inhibition capacity was investigated via sodium bentonite (Na-BT) plate soaking test, linear swelling experiment and hot-rolling dispersion experiment. The inhibition mechanism was analyzed by Fourier transforms infrared spectroscopy (FT-IR) analysis, X-ray diffraction (XRD) analysis, thermogravimetric (TGA) analysis, contact angle test, zeta potential test and surface tension measurement. The results demonstrated the shale hydration inhibition property of OMB was obviously superior to other widely used shale inhibitors. OMB could be easily adsorbed onto sodium montmorillonite (MMT) through electrostatic interaction, and some interlayer water molecules were expelled due to its intercalation. Meanwhile, the surface of MMT became more hydrophobic after adsorbed by OMB, and an effective shield against water intrusion was formed. In addition, OMB could effectively reduce the surface tension even at low concentrations, and a lower capillary suction pressure could be beneficial for reducing fluid invasion. The results obtained from the work indicated that OMB had the potential to become a high-performance shale inhibitor for drilling shale formations.

Hydrate dissociation poses a significant problem during drilling operations in hydrate-bearing sediments. The drilling fluid is in direct contact with hydrates, and understanding its inhibitory effect on hydrate dissociation is important for stabilizing hydrates during drilling operations. In this work, an apparatus was designed for investigating hydrate dissociation in drilling fluids, and the effects of thermodynamic hydrate inhibitors (THIs), polyvinyl pyrrolidone (PVP), and soybean lecithin on hydrate dissociation were studied. The inhibitory effect of a water-based drilling fluid in the presence of the potential hydrate dissociation inhibitors was also studied. An unexpected inhibitory effect occurred with ethylene glycol (EG) at concentrations below 10 wt%, resulting from a range of factors including the dissociation driving force, and mass and heat transfers in the EG solution. PVP and lecithin reduced the hydrate dissociation rate and increased the time required for complete dissociation of hydrates. These can, therefore, be used in water-based drilling fluids to inhibit hydrate dissociation. A combination of 0.1 wt% PVP and 0.5 wt% lecithin was selected as an optimal hydrate dissociation inhibitor, considering its inhibitory effect and compatibility with the drilling fluid. Using EG at a concentration below 10 wt% as a THI instead of NaCl can also help inhibit hydrate dissociation. The findings of this work provide a basis for the development and design of drilling fluids for drilling in hydrate-bearing sediments.

Filtration control of drilling fluid plays an important role in the process of wellbore construction and ensures the success of drilling operation. A swellable polymer microsphere (SPM) of methylmethacrylate (MMA), butyl acrylate (BA), and lauryl methacrylate (LMA) was synthesized with suspension polymerization. Its swelling property was characterized by oil adsorption capacity measurement. First, the effect of SPM on the filtration and rheological properties of virgin organic clay dispersion was investigated. Then the filtration and rheological properties of mineral oil-based drilling fluid in the presence of SPM were elucidated under the respective conditions of hot aging temperature, oil to water ratio and density. Furthermore, the filtration control properties between SPM and two traditional filtration loss additives including modified lignite and asphaltic additive was compared. Addition of SPM exhibited obvious influence on the viscosity of oil-based drilling fluid especially at high concentration of 3 w/v%, therefore, a concentration of lower than 1.5 w/v% was recommended. After hot aging at 200 °C, the oil-based drilling fluid containing 1 w/v% SPM exhibited an API filtration loss decrease of 85%, and HTHP filtration loss decrease of 79% in comparison with the base fluid. After hot rolling at 180 °C, the API filtration loss decreased by 2%, 24% and 53%, and the HTHP filtration loss decreased by 42%, 54% and 65% respectively when 1 w/v% asphaltic additive, modified lignite and SPM are in the presence of the base fluid. Besides decreasing the filtration loss volume under high temperatures, incorporation of SPM also improves the filter cake quality of oil-based drilling fluid. SPM is capable of adsorbing considerable base oil and become swellable. The swellable polymer microspheres with favorably deformable and compressible properties can effectively fill the voids of filter cake and reduce the permeability, which leads to low filtration loss and minimization of solids invasion.

Owing to superior temperature stability in comparison with water-based drilling fluids, oil or synthetic-based drilling fluids are generally preferred for high temperature and high pressure (HTHP) formations. However, the thermal degradation of emulsifiers and polymeric components under HTHP conditions that results in loss of rheological and filtration control, barite sag or even fluid phase separation also occurs. It is a challenge to sustain these properties stable under such harsh condition. Since nanoparticles have potential to provide better thermal stability, improved filtration loss as well as emulsion stability, the aim of this study is to investigate the effect of nano carbon spheres on the properties of oil-based drilling fluids under high temperature conditions. The nano carbon spheres were synthesized with the hydrothermal reaction of glucose. The influence of nano carbon spheres on the rheological, filtration, emulsion stability, settlement stability, as well as lubricity of a typical mineral oil-based drilling fluid with oil to water ratio of 80:20 was investigated before and after thermal aging at 180 and 200°C, respectively. The structure characterization showed that the uniform hard nano carbon spheres exhibited intermediate wettability. Laboratory performance test indicated that, for the oil-based drilling fluid, the addition of nano carbon spheres improved the rheological properties in terms of yield point and the ratio of yield point to plastic viscosity, which is beneficial for transporting of drilling cuttings. After thermal aging at 200 °C, the filtration loss volume was reduced as high as 70%, and desirable filter cake quality was obtained by incorporation of 1.0 wt% spheres, meanwhile the electrical stability was improved both before and after thermal aging. Furthermore, the fluid formulated with the nano carbon spheres generated better barite sag control. The polarizing microscope observation showed that the nano carbon spheres accumulated at the water-oil interface and formed a steric barrier which probably explained the reason of the above enhanced performance. The green synthetic routes and environmental friendly characteristics of the nano carbon spheres, in combination with the excellent properties suggested that the nano carbon spheres hold potential as multi-functional additives for formulating oil-based drilling fluids for HTHP drilling operations.

This paper is concerned with the formation of bitumen during the drilling of the H oilfield in Iraq. The high viscosity and strong adhesion properties of bitumen can influence the drilling operations. Some complex problems include paste screening, and drill pipe sticking, which cause huge economic losses. Therefore, it is necessary to effectively reduce the bitumen viscosity. The contribution of a single subcomponent of bitumen to the viscosity can vary, and the combined effect of different components of bitumen on the viscosity remains unclear. Furthermore, the mechanism of viscosity reduction remains unclear. In this study, the effects of organic solvents on the viscosity of bitumen were studied, and toluene was selected as the best organic solvent. The results showed that aromatics/resins, aromatics/asphaltenes, and resin/asphaltenes can help increase the bitumen viscosity. Novel methods, including the use of nanoparticles, ethyl cellulose, and the quaternary ammonium salt of heptadecenyl hydroxyethyl imidazoline (QASHI), were proposed to decrease the viscosity. TiO2 and CuO nanoparticles were chosen, and the main factors influencing the viscosity, such as the particle type, concentration, particle size, temperature, and shear rate, were analysed. The results show that the bitumen viscosity decreases with the increase in the concentrations of ethyl cellulose and QASHI. A synergistic effect between ethyl cellulose and QASHI was found with an optimal concentrations of ethyl cellulose and QASHI (1000 and 1600 mg L−1). A synergistic effect was also observed when nanoparticles, ethyl cellulose, and QASHI were used in combination. This paper reports the micro-mechanism whereby the viscosity of bitumen is decreased.

During the process of hydrate reservoir drilling, the heat generated by friction in a horizontal well section leads to hydrate decomposition and affects the wellbore stability. Consequently, the low-temperature environment of subsea wellbores can cause hydrate regeneration and flow obstacles. In this study, modified n-alkanes (MNA) with an appropriate phase transition temperature and acceptable latent heat were synthesised, and the thermal conductivity was improved by adding nano-Cu. A composite phase change material (PCM) was prepared using expanded graphite (EG) with adsorbing MNA, and nano-silica modification to improve its hydrophilicity and stability. Structural properties of the composite PCM were characterised via scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and nitrogen sorption. The DSC curves revealed an acceptable latent heat capacity and reliability of the prepared composite PCM. In addition, by simulating the temperature heating and cooling during the drilling process, the composite PCM exhibited a reasonable thermoregulating and hydrate decomposition inhibition performance, which can effectively inhibit hydrate decomposition in reservoirs and hydrate regeneration in wellbores. Moreover, the composite PCM exhibited a reasonable compatibility with the drilling fluid. The study results can be applied to realise intelligent temperature control and reduce the risk of drilling in hydrate reservoirs.

In order to solve wellbore instability problems in the drilling process, high-performance shale stabilizers in water-based drilling fluids are essential. In this paper, a novel shale stabilizer based on polyethylene glycol grafted nano-silica composite (PEG-NS) was successfully synthesized. Conventional techniques were used to characterize PEG-NS including Flourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), particle size distribution (PSD) and thermogravimetric analysis (TGA). The results showed that the structure of PEG-NS was in agreement with the design objective. The particle size of PEG-NS ranged from 110 to 434 nm, and PEG-NS had good thermal stability. Pressure transmission test, pore structure characterization of shale, rolling recovery test were applied to evaluate the comprehensive performance of PEG-NS as a novel shale stabilizer. The experimental data indicated that PEG-NS could effectively retard the pore pressure transmission and reduce the permeability of shale sample. PEG-NS could adsorb onto the shale surface and a dense plugging film could finally coat on it. Moreover, PEG-NS also exhibited better inhibition performance compared with that of potassium chloride (KCl) and polymeric alcohol (JHC) at the same concentration. Hence, PEG-NS could be a good shale stabilizer in water-based drilling fluids for drilling reactive shale formations.

To convert the hazardous and waste oil sludge into shale stabilizer using in drilling fluid, a novel preparing method has been proposed in the current study. According to the characteristics of oil sludge, the preparation procedure was designed learning from conventional asphaltic-type shale stabilizer preparation method. Several additives such as gilsonite, calcium carbonate, surfactants (hexadecyltrimethylammonium chloride (CTAC) and polyoxyethylene octylphenol ether (OP-10)), polymers (polyethylene glycol (PEG-2000) and cationic polyacrylamide (CPAM)), and fluid loss reducers (sulfonated lignite and potassium humate) were incorporated into oil sludge with the assistance of melting, stirring, kneading, and drying. After the sequential steps of asphaltization, emulsification, and stabilization, a powdered shale stabilizer product (SS-OS) was obtained. The effect of SS-OS on rheology, filtration, and lubricity of drilling fluid bentonite dispersions was tested. Furthermore, the properties of stabilizing shale were evaluated. The results indicated that SS-OS could effectively inhibit shale swelling, dispersion, and exhibit excellent sealing performance. Moreover, it helped to reduce the fluid loss and significantly improve the lubricity of the drilling fluid. From the preliminary study, it was concluded that the strategy of preparing shale stabilizer with oil sludge could be employed to overcome waste, energy and environmental problems simultaneously and show promising application.

Interest in using nanomaterials to improve shale stability during drilling operations has been increasing. Herein, a polymer microsphere emulsion (PME) as a high-performance shale stabilizer for water-based drilling fluids (WDFs) was prepared via emulsion polymerization. The particle sizes in PME in aqueous solution ranged from 90 to 320 nm. PME was found to exhibit excellent salt tolerance and temperature resistance. The plugging performance of PME was tested through pressure transmission tests. The results indicated that the polymer microspheres in PME could effectively plug shale pores and reduce shale permeability. In addition, rolling recovery tests were used to evaluate the shale hydration inhibition performance of PME. It was found that PME showed great performance for decreasing shale hydration potential. These factors make PME a promising shale stabilizer for WDFs used to drill shale formations.

Effective filtration loss control is a challenge for water-based drilling fluid when drilling high temperature and high pressure (HTHP) formations. After thermal aging at 200 °C for varying times, the static filtration loss controlling capabilities of β-cyclodextrin polymer microspheres (β-CDPs) and synthetic polymer Driscal-D in bentonite suspensions were compared in this study. A comprehensive physicochemical characterization was presented using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), particle size distribution, zeta potential, electrical conductivity and scanning electron microscope (SEM). The results indicated that when exposure to thermal aging of 200 °C, the filtration loss of bentonite suspension increased with the initial 6 h of aging, after that it increased slightly. While for synthetic polymer Driscal-D, the filtration loss increased gradually with thermal aging time until to 36 h. In contrast for β-CDPs, the filtration loss increased firstly and then decreased and maintained relatively stable after thermal treatment for 6 h. High temperature destroyed the hydrated structure of bentonite particles and induced the increase of filtration loss volume. In viewing of Driscal-D, degradation of the polymer in combination with dehydration of bentonite particles led to the gradual losing of suspensions stability. For β-CDPs, after aging of 6 h, the hydrothermal carbonization reaction generated numerous nano and micro carbon spheres and bentonite-carbon sphere composited structures, which fill in the gaps between the larger particles and contribute to reducing the filter cake permeability. This result identified that β-CDPs are superior to synthetic polymer Driscal-D in filtration control when subjected to long term high temperature environments.

The friction heat generated during the drilling process of natural gas hydrate bearing sediment (HBS) leads to the temperature of drilling fluid higher than the phase equilibrium temperature of hydrate, which induces hydrate decomposition and wellbore instability. In this work, tetrabutylammonium bromide (TBAB) and Nano-silica were microencapsulated by inverse emulsion interfacial polymerization. The effect of different preparation conditions on the encapsulation rate of microcapsules was characterized by differential scanning calorimetry (DSC), and the highest encapsulation rate was 62.2% with the melting enthalpy of 121.4 J/g. Polarizing microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM) images were used to characterize the synthesis process and microstructure of microcapsules, which proved a quasi-spherical structure coated with Nano-silica. Furthermore, it was confirmed that the microcapsules also had good thermal conductivity, reliability and thermoregulating performance. The rheological parameters of drilling fluid with 5 wt% microcapsules increased slightly, and the filtration loss decreased, indicating good compatibility. In addition, it is convenient to adjust the melting temperature of the core materials by adding NaCl with different concentrations. This study is of guiding significance to realize intelligent temperature-control of hydrate bearing sediment during drilling.

Inhibiting hydrate decomposition due to the friction heat generated by the drilling tools is one of the key factors for drilling hydrate formation. Since the existing method based on chemical inhibition technology can only delay the hydrate decomposition rate, a phase-change microcapsule was introduced in this paper to inhibit, by the intelligent control of the drilling fluid temperature, the decomposition of the formation hydrate, which was microencapsulated by modified n-alkane as the core material, and nano-silica was taken as the shell material. Scanning electron microscope (SEM), size distribution, X-ray diffraction (XRD), and Fourier transform infrared spectrometer (FT-IR) were utilized to characterize the structural properties of microcapsules. Differential scanning calorimetry (DSC) spectra displayed that the latent heat was 136.8 J/g in the case of melting enthalpy and 136.4 J/g in the case of solidification enthalpy, with an encapsulation efficiency of 62.6%. In addition, the prepared microcapsules also showed good thermal conductivity and reliability. By comparison, it was also proved that the microcapsules had good compatibility with drilling fluid, which can effectively control the temperature of drilling fluid for the inhibition of hydrate decomposition.

The surface hydration of shale has severe effect on the wellbore stability during drilling through the shale formation. In this paper, a novel method was developed to measure wettability of shale power by determining real contact angle. A variety of methods including measurements of Zeta potential, uniaxial compressive strength, shale stability indexes, surface hydration water, linear swelling, and cuttings hot-rolling dispersion experiment were used to evaluate the inhibition of surfactants. Meanwhile, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction analysis (XRD) were used to investigate the interaction between surfactants and shale particles. Results revealed that the surface hydration of shale could be inhibited by using suitable surfactants. The surfactants compound of PA and THAO possessed stronger surface hydrating inhibition and capacity of restraining osmotic hydration. This is because the compound can enhance the surface hydrophobicity after adsorption onto the surface of shale particles, restrained osmotic hydration through swapping out inorganic cations in the clay interlayer, thus reducing the zeta potential and bounding clay gall together.

In this paper, a novel hydrophobic modified polymer based silica nanocomposite (NFC) was successfully prepared by emulsion polymerization and it was characterized by FTIR, PSD, TEM and TGA analysis. The results indicated that NFC possessed uni-modal distribution from 38 nm to 164 nm with the D50 value of about 72 nm and had good thermal stability. A variety of methods including the contact angle measurement, pressure transmission test, hot-rolling cuttings dispersion test and compatible test were adopted to evaluate the comprehensive effect of NFC on shale stability. And the shale cores before and after interacting with NFC were also characterized by scanning electron microscope (SEM) analysis. The experimental investigations revealed that NFC could effectively retard the pore pressure transmission and internally bridge and seal the pore-throats of shale. And it also exhibited preferable shale inhibition performance compared with KCl and JHC at the same concentration. After adsorption, the shale surface was more hydrophobic, which was more advantageous to shale stability. Furthermore, the compatibility test results confirmed that NFC had no negative effect on rheological performance and possessed a positive influence on filtration control performance of water-based drilling fluids.

Since 2007, heterogeneous, high-viscosity active bituminous formations have often occurred during the drilling process in Yadavaran oilfield (Iran), Halfaya oilfield (Iraq), and tar sands (Canada). The formation of bitumen exhibits plastic and creep properties, and its adhesion is strong, so drilling accidents are easily caused, such as adhering vibrating screen, drill pipe sticking, lost circulation, and even well abandonment. These complex problems cause huge economic losses. Solvents used to dissolve bitumen are a feasible technology to remove bitumen effectively. In order to solve this problem, we used crude bitumen samples from Halfaya oilfield to study the relation between the bitumen component and different solvents. In this study, the temperature, crude bitumen sample to solvent ratio, stirring rate, stirring time, and ultrasound time on bitumen recovery by toluene were investigated by a single factor experiment. The optimum process parameter for bitumen recovery was obtained. Toluene, n-heptane, tetrahydrofuran, cyclohexane, cyclopentane, ethyl acetate, and n-pentane were chosen as the solvents for single solvent extraction and composite solvent extraction. The bitumen recovery increased significantly with the use of a composite solvent compared to a single solvent. The composite solvent ratio was 1:1. The highest bitumen recovery was 98.9 wt% by toluene/cyclohexane composite solvent. The SARA (saturates, aromatics, resins, and asphaltenes) components of the bitumen were analyzed. The toluene showed the highest asphaltene content, while the n-alkanes showed the lowest asphaltene content. The higher the asphaltene content, the higher the bitumen recovery. The composite solvent obtained the highest asphaltene content and bitumen recovery. The viscosity of bitumen extraction by different solvents was measured. The lower the bitumen viscosity, the higher the bitumen recovery. The element analysis indicated the solvent&rsquo, s ability to extract bitumen colloids with the C/H ratio. This study provides a reliable theoretical basis for the subsequent adoption of effective anti-bitumen polluted drilling fluid additives.

With increasingly stringent environmental regulations, an environmentally friendly and high performance filtration loss reducer for water-based drilling fluid is essential. This study aims to investigate the potential of utilizing starch nanospheres (SNSs) in this capacity. SNSs were fabricated by a crosslinking reaction between soluble starch and methylene-bis-acrylamide (MBA) using an inverse emulsion polymerization. The structure of SNSs was characterized with Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size distribution measurement and thermogravimetric analysis (TGA). The effect of SNSs on the rheological and filtration properties of bentonite-based drilling fluid was investigated according to American Petroleum Institute (API) standards. Three-dimensional nearly spherical particles about 100–300 nm with smooth surface were formed after the inverse emulsion polymerization. SNSs had little influence on the rheological properties of bentonite-based drilling fluids. After subjected to thermal aging at 150 °C, SNSs still exhibited stable and effective filtration control. Viscosity and filtration loss were lower as well, and the performance after aging was better than currently used modified starch filtration reducers that were tested. The nano particles readily plugging micropores of filter cake and water absorbency ability as well as deformability and elasticity resulted in the effective filtration control. SNS has the potential to be used as biodegradable filtration loss reducer in elevated temperature formations replacing commercially available starch derivatives.

API bentonite, a key ingredient of drilling muds, displayed a negative zeta potential across the whole pH range of 2.5–12.3. It contained two very rheological active ingredients, sodium montmorillonite or Na+Mt (40.4%) and needle-shape sepiolite (16%). Due to the interplay of these two ingredients, the rheological behaviour displayed by the API bentonite suspensions is quite different to other bentonite suspensions. The gel displayed a very low or no yield stress at low acidic pH and a maximum yield stress at pH 8–12. Magnesium leaching from sepiolite at low pH and its hydrolysis plays a role in affecting the rheological properties at high pH. Yield stress and ageing behaviour was observed in suspensions with at least 3 wt% solids. The Herschel-Bulkley (HB) model described the flow behaviour of these gels. Both the HB yield stress and viscosity at a fixed shear rate of the 7 wt% gel peaked at pH 8.5 and were smallest at pH 5.2. The ageing or structural recovery behaviour is most pronounced at high pH for the most concentrated gels. Both the Leong and Nguyen-Boger ageing models described the structural recovery behaviour well. The recovery of the recently discovered very open honeycomb structure formed by Na+MT gel, after breakdown by shear was invoked to explain the ageing behaviour.

Wellbore instability due to shale hydration and dispersion is always a challenge in oil and gas drilling engineering. Hydroxyl-terminated polyamidoamine (PAMAM-OH) dendrimers were probed as potential shale inhibitors for the first time. The inhibitive potential of candidate PAMAM-OH dendrimers was screened with particle size distribution test, bentonite inhibition test, and cuttings dispersion test. In order to reveal the underlying inhibitive mechanism, the interaction between the dendrimers and sodium bentonite (Na-Bent) was characterized using X-ray diffraction analysis, zeta potential measurement, and thermal gravimetric analysis. The results indicated that PAMAM-OH dendrimers could intercalate into bentonite particles. The intercalation can form in mono or bilayer arrangement. The deformation of bentonite increased with the intercalated number of layers and affected by the phase variety and the change in adsorbed concentration. When adopting monolayer adsorption in the interlayer, the dendrimers exhibited effective inhibition performance, while the bilayer adsorption corresponded to decreased inhibitive performance. Marked improvement in shale inhibition was realized when a routinely used shale inhibitor KCl and PAMAM-OH were combined. A stable monolayer intercalation of dendrimers was observed in the presence of KCl, suggesting a synergetic effect between PAMAM-OH dendrimers and KCl.

In order to develop high-performance water-based drilling fluid with the aim of meeting the increasing requirement of drilling industry, highly inhibitive and high-temperature-resistant shale inhibitors are essential. In this study, 4, 4′-methylenebis-cyclohexanamine was introduced as a potential shale inhibitor. The inhibitive properties of the amine compound in comparison with currently available polyether diamine inhibitor were evaluated using bentonite inhibition test, shale cuttings hot-rolling dispersion test, linear swelling test, and pressure transmission test. The inhibitive mechanism was investigated with zeta potential measurement, X-ray diffraction analysis, and contact angle measurement. The results indicated that 4, 4′-methylenebis-cyclohexanamine can inhibit shale hydration and dispersion effectively, and prevent pressure transmission to a certain extent, performing better than that of polyether diamine. Furthermore, the new diamine provides reliable thermal stability as high as 220 °C, preserving the benefits of high-temperature wells application. This novel diamine inhibits shale hydration and dispersion with the combination of chemical inhibition and physical plugging. The intercalation into the interlayer of clay with monolayer collapses the hydrated clay structure and expels the water molecules. After adsorption, clay surface became more hydrophobic, which prevents the imbibition of water. The variation of solubility separates the compound from the solution, which can plug the micro-pores of shale and prevent fluid invasion.

Controlling the filtration of water-based drilling fluid effectively in high temperature environment is a great challenge in drilling engineering. In this study, β-cyclodextrin polymer microspheres (β-CDPMs) were synthesized by crosslinking between β-cyclodextrin and epichlorohydrin via inverse emulsion polymerization and employed as filtration reducers. The standard American Petroleum Institute filtration test showed that the β-CDPMs can only perform the enhanced filtration control ability at temperatures above 160 °C, and can tolerate the temperature resistance up to 240 °C without significant influence of rheology. As the thermal aging temperature is above 160 °C, numerous nano carbon spheres and nanostructured composites generated due to the occurrence of hydrothermal reaction. These high temperature stable nanoparticles bridged across the nano sized gaps and participated into forming dense filter cake, contributing to excellent filtration control. The filtration control mechanism proposed in this study opened a novel avenue for high temperature filtration control in water-based drilling fluids.

Shale hydration and dispersion leading to wellbore instability is always a challenge in oil and gas drilling engineering. In this study, specifically designed nano-particles by grafting hyperbranched polyethyleneimine (Mw = 600) onto the surface of nano-silica particles were synthesized. The modified nano-particles were characterized with Fourier transform infrared spectrum (FT-IR), particles size distribution measurement, thermal gravimetric analysis (TGA), transmission electron microscope (TEM) and zeta potential measurement. The results indicated that after modification, the nano-particles became positively charged and showed better dispersion in water compared to pristine nano-silica particles. Shale cuttings hot-rolling dispersion test and linear swelling test as chemical inhibitive tests in combination with pressure transmission test and shale sample spontaneous imbibition test as physical plugging tests were used to evaluate the shale stabilizing performance of the modified nano-particles. The results showed that the modified nano-particles exhibited both effective chemical inhibition and physical plugging, whereas nano-silica only showed limited physical plugging. The interaction between modified nano-silica particles and shale demonstrated that the grafted hyperbranched polymer strongly adsorbed onto the clay surface via electrostatic interaction and hydrogen bonding, which resulted in effective inhibition of shale hydration and swelling. After adsorption, the modified nano-silica particles were trapped on the micropores of shale formation and prevented the fluid invasion. The dual functions of the modified nano-silica particles demonstrated a remarkable improvement of shale stability.

β-cyclodextrin polymer (β-CDP) microspheres were investigated as high temperature resistant filtration reducers for water-based drilling fluid in this study. The microspheres were synthesized by crosslinking reaction between β-CD and epichlorohydrin with inverse emulsion polymerization. The structural and morphological characteristics of the prepared microspheres were examined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), particle size distribution measurement, and thermogravimetry analysis (TGA). The filtration control properties of the microsphere were evaluated via American Petroleum Institute (API) filtration test and high temperature and high pressure (HTHP) filtration test. The results indicated that β-CDP microspheres could effectively reduce the filtration of bentonite suspension both before and after thermal aging at 200 °C without significant influence on drilling fluid's rheology. A substantially enhanced filtration control behavior was observed after thermal aging, which was contrary with conventional filtration reducers. The β-CDP microspheres could absorb a large number of water and became swellable and deformable, which enhanced the compressibility of filter cake. What is more, hydrothermal reaction occurred for part of β-CDP microspheres under high temperature environment, resulting in the formation of numerous carbon spheres ranging from hundreds of nanometers to several micrometers. The β-CDP microspheres, bentonite particles and small carbon spheres in combination contributed to form a dense and compact filter cake with low permeability. β-CDP microspheres were potential candidates as environmental friendly and high temperature filtration reducers in deep well drilling.

The currently available liquid lubricants used in drilling fluids are generally troubled by the inferior anti-high temperature, complex preparation, high foaming ratio, and fluorescence grade, which suppress the effective extension of the drilled hole and lower the drilling efficiency. This paper, with liquid paraffin as the oil phase, mixed Span 80 and Tween 80 as primary surfactants, the normal butanol as the secondary surfactant, and the Gemini quaternary ammonium compound-based surfactant GTN as the emulsion electrical regulator, developed a microemulsion lubricant, referred to as NE. The basic characteristics of such lubricant were analyzed using the Zetasizer Nano ZS90, and its lubrication performance, thermal stability, foaming ratio, fluorescence grade, and compatibility with drilling fluids were evaluated through laboratory experiments. Results showed that the nanodroplets formed in the diluted microemulsion lubricant NE were positively charged, with an average diameter of 187–258 nm. With 2% of NE, the coefficient of friction of the bentonite drilling fluid dropped by 83.8%, and the mud cake adhesion factor by 74.2%. The lubricant was featured by excellent thermal stability and was active in conditions with temperature as high as 160 °C. Moreover, with a low foaming ratio and weak fluorescence, the lubricant was well compatible with various drilling fluids, and met the field application requirement of drilling fluids.

Research on using nanotechnology to solve shale instability problems in drilling engineering has been increasing. The combination of amphiphilic polymer and silica nanoparticles may be a new way to improve shale stability. Herein, an amphiphilic polymer/nano-silica composite (poly(styrene-methyl methacrylate-acrylamide)/nano-SiO2) was introduced as a novel shale stabilizer SMA/SiO2 for water-based muds, which possessed the advantages of both physical plugging and chemical inhibition during the drilling operations. The SMA/SiO2 was prepared and characterized by Fourier transform infrared spectra (FT-IR), nuclear magnetic resonance (1H-NMR), transmission electron microscope (TEM), particle size distribution (PSD) and thermogravimetric analysis (TGA) experiments, which confirmed that SMA/SiO2 was regularly spherical with nano-scale and showed good high-temperature resistance. To evaluate the plugging capacity of SMA/SiO2, the pressure transmission test and BET analysis were applied. The results indicated SMA/SiO2 was capable of effectively plugging the pores and fractures in shale. To evaluate the hydration inhibition capacity of SMA/SiO2, the rolling dispersion experiment and contact angle test were adopted. The results demonstrated that SMA/SiO2 could reduce the tendency of shale hydration, which was better than potassium chloride (KCl) and polymeric alcohol (JHC). In addition, SMA/SiO2 only created slight variations on the rheological parameters of the water-based muds (WBMs) and showed a significant filtration control performance. Due to the outstanding performance of physical plugging and chemical inhibition, SMA/SiO2 was expected to be a novel shale stabilizer to solve shale instability problems.

To investigate the interaction mechanism, clay inhibition and compatibility of sodium silicates as shale inhibitor in water based drilling fluid, a variety of properties were characterized. Zeta potential, activity, colloidal stability and particle size were employed to characterize the colloidal properties. Adsorption, cuttings hot-rolling dispersion, linear swelling, pressure and osmosis transmission tests were used to determine the inhibition properties. Results showed that the zeta potential of sodium silicate solution ranging from −45 mV to 0 mV, increased in magnitude with increasing the sodium silicate modulus and pH of solution in the initial stage and decreased with the concentration of monovalent inorganic salts. With the increase of modulus and concentration of sodium silicate, the solution activity generally decreased or colloidal polysilicic acid began to form at a solution concentration above 70 g/L of Na2O⋅2.8SiO2 (2.8SS). The diameter of polysilicic acid increased with 2.8SS concentration, modulus, pH and salt concentration. Adsorption of 2.8SS onto montmorillonite through chemical bonding was boosted with increasing 2.8SS concentration regardless of cuttings addition. The adsorption also rose exponentially with temperature. The activity of the montmorillonite suspension was reduced by the addition of 2.8SS and further decreased by salt addition. 2.8SS was found to exhibit superior inhibition performance compared to KCl, organosilicon, sulfonate asphalt and polyglycol. The pressure transmission was retarded effectively, resulting in the improvement of membrane efficiency of shale clays.

In this paper, novel latex particles and aluminum complexes as potential shale stabilizers in water-based drilling fluids were successfully synthesized and characterized in detail. The spherical latex particles were prepared by emulsifier-free polymerization of styrene and methyl methacrylate, and it possessed uni-modal distribution from 80 nm to 345 nm with the D90 value of 276 nm. The aluminum complexes were synthesized through the complexation reaction of humic acid with sodium aluminate and it could be completely soluble under alkaline conditions, and aluminum hydroxide and humic acid flocculate would precipitate from the filtrate under neutral or acidic conditions or interacting with magnesium or calcium ion. The synergistic effect on shale stability of latex particles and aluminum complexes was investigated quantitatively through the pressure transmission and membrane efficiency tests. The pore structure of shale cores before and after testing was also characterized via nuclear magnetic resonance core analysis and scanning electron microscope analysis. The results indicated that the latex particles as physical shale stabilizer could be deformable to internally bridge and seal micro–nano scale pore-throats and fractures of shale, and the aluminum complexes as chemical shale stabilizer would precipitate from the filtrate when exposed to pore–fluids and the precipitation could also plug and seal pore-throats and micro-fractures. The latex particles work synergistically with aluminum complexes to impart shale stability due to superior properties of decreasing shale permeability and increasing shale membrane efficiency. Furthermore, the compatible test results confirmed that novel latex particles and aluminum complexes could be alternatives to standard shale stabilizers in water-based drilling fluids.

Polyetheramines as shale hydration inhibitors in water-based drilling fluids have attracted great interests in recent years. In this paper, in order to clarify the relationship between inhibitive properties and molecular structures of polyetheramines, several inhibitive experimental methods including bentonite inhibition test, shale cuttings hot-rolling dispersion test, sedimentation volume measurement, and API filtration measurement were adopted to evaluate the inhibition variation of different polyetheramines. Furthermore, a series of analytical methods such as surface tension determination, zeta potential measurement, XRD, contact angle measurement, and water adsorption test were performed to identify the relationship between the inhibitive performance and molecular structures. The factors including molecular weight, number of amine group, and molecular chain affecting the interaction between polyetheramines and clay particles were analyzed. Polyetheramine with molecular weight of 230 and oxypropylene segment can reduce the interlayer spacing of the hydrated clay to the minimum and exhibit the best performance in comparison with others. The coordination of electrostatic adsorption with monolayer arrangement, hydrogen bonding, and hydrophobic shielding effect contributed to the top level of inhibition.

The amine terminated polyamidoamine (PAMAM) dendrimers were investigated as potential shale stabilizers for the first time. Its inhibitive properties were characterized by a bentonite inhibition test and a shale cuttings dispersion test. The interaction between PAMAM dendrimers of various generations and sodium bentonite was examined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The hydration and dispersion of shale can be effectively inhibited with PAMAM dendrimers. The decrease of pH value in the dendrimer aqueous solution improved the inhibitive performance. For lower generations of dendrimer growth (G0 to G3), the inhibitive level decreased with the increase of generation. For higher generations (G4, G5), the inhibitive level increased with the increase of generation. Low generation PAMAM dendrimers could penetrate into the clay interlayer space, but exhibited highly oblate intercalation behaviors. G0 intercalated into the interlayer space with a monolayer conformation as concentration increased, while G1, G2, G3 and G4 intercalated into the interlayer space with monolayer arrangement at low concentrations, and mixed phase orientation at high concentrations. G5 could not fully intercalate into the interlayer space due to the steric hindrance. According to the interaction between PAMAM and clay, effective internal and external inhibition on shale hydration and dispersion could be obtained with the combination of low generation G0 and high generation G5. A new water-based drilling fluid including G0 as shale swelling inhibitor and G5 as shale dispersion inhibitor was established and exhibited excellent inhibitive properties.

In the preparation of a hydrophobic bentonite, the clay was first purified and then converted to sodium form with sodium fluoride before being made hydrophobic by intercalation with octadecyl dimethyl phenylmethyl ammonium chloride (ODPAC). Elemental and mineral compositions of the sodium-modified bentonite were determined using X-ray fluorescence spectrometry (XRF) and X-ray diffraction (XRD). The swelling capacity and colloid index were also determined. For the hydrophobic bentonite, the following were characterised microstructure, interlamellar spacing, composition, thermal stability, wettability, surface energy and dispersity using a range of techniques: SEM, XRD, FTIR, thermogravimetric analysis (TGA) and contact angle. The colloid fraction and rheological properties were also determined. Sodium modification caused a certain increase in clay and Na2O contents and decrease in quartz content. The interlamellar spacing was also decreased to 10.03 A. Hydrophobic bentonite displayed a larger interlamellar...

Nano or micro-nano-based materials have attracted a strong interest due to its attractive properties and they have great potential for developing intelligent drilling fluid in petroleum industry. In this article, a novel hydrophobic associated polymer based silica nanoparticles composite with core–shell structure which was mainly used for developing intelligent drilling fluid additive for drilling ultra-deep well under ultra-high temperature, ultra-high pressure and salinity, was prepared with Acrylamide, 2-Acrylamide-2-methylpro pane sulfonic acid, Maleic anhydride, Styrene and silica nanoparticles via inverse micro emulsion polymerization and sol–gel preparation, and was characterized by particle size distribution, SEM, TEM ESEM and the influence law of comprehensive performance of water based drilling fluid and its mechanism influenced by novel hydrophobic associated polymer based silica nanoparticles composite were studied too. Micro-model drilling fluid flooding and drilling fluid displacement experiment of core column were adopted to assess the plugging stability of micro-pores and micro-cracks and effect on wellbore stability. The experimental data showed that, the composite as a micro-nano-drilling fluid additive, possessed excellent properties such as thermal stability, rheology, fluid loss and lubricity. Especially, it could plug the formation effectively and improve the pressure bearing capability of formation significantly.

The influence of common thermodynamic hydrate inhibitors including NaCl, glycol and glycerol on the hydrate inhibition performance of PVP (poly (vinyl pyrrolidone)) in deepwater drilling fluid was experimentally studied, and the synergism of NaCl on the performance of PVP was further investigated. Results of tests demonstrated that as the representative of the first generation of kinetic hydrate inhibitors, PVP could prolong the induction time and lower the rate of hydrate growth. NaCl showed strong synergistic effect on the performance of PVP, while glycol and glycerol were not the right synergists in comparison with NaCl. The presence of NaCl enhanced both the hydrate nucleation inhibition and growth inhibition strength of PVP, thus giving a several time longer induction time with lower pressure drop rate. For deepwater drilling fluid containing 0.5 wt% PVP, the addition of 10 wt% NaCl could prolong the induction time from approximately 60 min to more than 1000 min at either the same water depth condition (2 °C, 10 MPa) or same subcooling (14.2 °C). At higher subcooling (16.4 °C), the synergistic effect was still strong, and the combination of 10 wt% NaCl and 1.5 wt% PVP could give a 600 min induction time. The long induction time is considerable for safe deepwater drilling at different water depth.

In order to improve the inhibitive properties and high temperature resistance of shale inhibitor, cycloaliphatic amines were introduced as shale hydration inhibitors in water-based drilling fluids. Bulk hardness test, shale cuttings dispersion test, bentonite inhibition test and water adsorption test were carried out to characterize the inhibitive properties of the novel amines. Surface tension measurement, zeta potential measurement, XRD, contact angle test, SEM and TGA were performed to investigate the interaction between the cycloaliphatic amines and clay particles. The results indicated that cycloaliphatic amines exhibited superior inhibitive properties to the state of the art inhibitors. Moreover, the amines were high temperature resistant. The hydrophobic amine could intercalate into the clay gallery with monolayer orientation. The protonated ammonium ions neutralized the negatively charged surface. After adsorption, the hydrophobic segment covered the clay surface and provided a shell preventing the ingress of water.

We have experimentally investigated a number of properties of polyglycol in deepwater drilling fluids. Polyglycol retards pressure transmission from the fluid to the formation, and improves the shale cuttings recovery rate. Measurements of the electrokinetic potential (the zeta potential) and the clay particle size showed that the inhibiting effect of polyglycol involves adsorption on clay particles and plugging pores and cracks. Polyglycol inhibits gas hydrate formation, has good lubricity and low toxicity, and does not have a significant impact on the rheological properties of drilling fluids at low temperature.

Novel hydrophobically modified polyacrylamide (HMP) copolymers based on octadecyl dimethyl allyl ammonium chloride (C18DMAAC) were synthesized by homogeneous polymerization. The sealing performance of the HMP as sealing agent in drilling fluid was studied. The results showed that HMP-3 containing 0.66% (molar ratio) hydrophobic monomer gave the best sealing property. Compared with the traditional sealing agent, HMP-3/clay could seal the cores of different permeabilities effectively by forming a low-permeability barrier with the help of bridge material. Permeability recovery test indicated that the recovery rate of cores treated by HMP-3 systems was over 90%. The particle size analysis showed that the grain distribution of drilling fluid system can be changed by HMP-3, and the system containing HMP-3 component covered a much wide distribution, so it can be used in a wide range of pore sizes and permeabilities without foreseeing the size of pore throat definitely. This work has provide a new idea to solve t...

A novel aluminum-based shale stabilizer used in drilling fluid composed of humic acid and aluminum (HA-Al) was synthesized. The expansion rate of shale sample in HA-Al solution was 12.87% (23.21% in pure water) in linear expansion test. Shale stability index values of high water content and low water content samples were 73.00 and 55.94, respectively, indicating HA-Al had good inhibition performance by absorbing between clay particles. The pore pressure transmission test indicated that after 20 h, the result was 0.4 MPa in glycols solution, 0.15 MPa in sodium silicate solution, and 0.07 MPa in HA-Al solution. Obviously, the last one was the best. So HA-Al had excellent performance to reduce pore pressure transmission. By scanning electron microscopy and energy-dispersive spectrometer analysis, it was confirmed that HA-Al could precipitate in the shale pores. As a result, the pore pressure transmission reduced and the shale stability increased.

Based on the rules of designing high performance shale inhibitors, bis(hexamethylene)triamine was introduced as a potential shale inhibitor in water-based drilling fluid. The inhibitive properties were evaluated through bentonite inhibition test, cuttings hot-rolling dispersion test and particle distribution measurement. The compatibility with common drilling fluid additives was investigated. Bis(hexamethylene)triamine effectively inhibited shale swelling and dispersion, superior to potassium chloride and polyetherdiamine POP230, and was compatible with normal additives in drilling fluid. The inhibitive mechanism was analyzed via XRD, zeta potential measurement, FT-IR, water adsorption test and TGA. The results showed that electrostatic interaction, hydrogen bonding and hydrophobic shielding effect contributed to the inhibition with synergetic effects, whereas the protonation of multi-amine groups played a vital role in the action.

A novel aluminum-based shale stabilizer used in drilling fluid composed of humic acid and aluminum (HA–Al) was synthesized. HA–Al is soluble under alkaline conditions, however, it can precipitate as microsphere pseudoboehmite and humic acid floc under neutral and acidic conditions or after the addition of Ca 2+ and Mg 2+ ions in solution. Due to these chemical features, HA–Al can dissolve in drilling fluid and precipitate in the shale pore throats when exposed to shale pore fluid to reduce pore pressure transmission, as is proven by SEM test. Comparing to other two samples of sodium silicate and poly alcohol, HA–Al is the best one to maintain wellbore stability due to its better properties of decreasing pore pressure transmission and increasing actual osmotic pressure of shale sample, as is indicated by pore pressure transmission and shale membrane efficiency tests.

In deepwater oil and gas drilling, the high-molecular-weight encapsulator aggravates the thickening of the drilling fluid at low temperatures. Therefore, it is hard to manage the downhole pressure, and drilling fluid loss occurs. In this paper, a zwitterionic polymer P(AM-DMC-AMPS) which was the terpolymer of acrylamide, methacrylatoethyl trimethyl ammonium chloride, and 2-acrylamido-2-methylpropane sulfonic acid, was developed as a low-molecular-weight encapsulator. It was characterized by Fourier transform infrared spectrum analysis, nuclear magnetic resonance, and gel permeation chromatography. Moreover, the low-temperature rheology, shale inhibition and filtration properties of water-based drilling fluids (WBDFs) containing different encapsulators were experimentally investigated and compared. The results showed that the molecular weight of P(AM-DMC-AMPS) was about 260,000, much lower than that of the conventional encapsulators. In the deepwater drilling temperature range 4–75 °C, WBDF containing P(AM-DMC-AMPS) had lower and more stable rheological property because of its short molecular chains. The high shale recovery rate and low swelling rate indicated its strong shale inhibition performance, owing to its adsorption on the clay surface and the wrapping effect through both hydrogen bonding and electrostatic interaction. It also improved the filtration property of WBDF, and was compatible with other WBDF components. This product is expected to simultaneously realize the good encapsulation performance and low-temperature rheological property for deepwater drilling fluid.

The poly(styrene-methyl methacrylate) latex particles as potential physical shale stabilizer were successfully synthesized with potassium persulfate as an initiator in isopropanol-water medium. The synthesized latex particles were characterized by Fourier transform infrared spectroscopy (FT-IR), particle size distribution measurement (PSD), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). FT-IR and TGA analysis confirmed that the latex particles were prepared by polymerization of styrene and methyl methacrylate and maintained good thermal stability. TEM and PSD analysis indicated that the spherical latex particles possessed unimodal distribution from 80 nm to 345 nm with the D90 value of 276 nm. The factors influencing particle size distribution (PSD) of latex particles were also discussed in detail. The interaction between latex particles and natural shale cores was investigated quantitatively via pore pressure transmission tests. The results indicated that the latex particles as potential physical shale stabilizer could be deformable to bridge and seal the nanopores and microfractures of shale to reduce the shale permeability and prevent pore pressure transmission. What is more, the latex particles as potential physical shale stabilizer work synergistically with chemical shale stabilizer to impart superior shale stability.

Emulsifier-free poly(methyl methacrylate–styrene) [P(MMA–St)] nanospheres with an average particle size of 100 nm were synthesized in an isopropyl alcohol–water medium by a solvothermal method. Then, through radical graft copolymerization of thermo-sensitive monomer N-isopropylacrylamide (NIPAm) and hydrophilic monomer acrylic acid (AA) onto the surface of P(MMA–St) nanospheres at 80 °C, a series of thermo-sensitive polymer nanospheres, named SD-SEAL with different lower critical solution temperatures (LCST), were prepared by adjusting the mole ratio of NIPAm to AA. The products were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, particle size distribution, and specific surface area analysis. The temperature-sensitive behavior was studied by light transmittance tests, while the sealing performance was investigated by pressure transmission tests with Lungmachi Formation shales. The experimental results showed that the synthesized nanoparticles are sensitive to temperature and had apparent LCST values which increased with an increase in hydrophilic monomer AA. When the temperature was higher than its LCST value, SD-SEAL played a dual role of physical plugging and chemical inhibition, slowed down pressure transmission, and reduced shale permeability remarkably. The plugged layer of shale was changed to being hydrophobic, which greatly improved the shale stability