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The construction of Zhongyuan gas storage group takes the salt layer as the caprock. Therefore, the cementing quality of the sealed salt interval is a key factor in the construction of gas storage. The cement slurry was eroded by the salt gypsum layer during the migration of the salt layer, which affects the basic performance of cement slurry, resulting in the poor cementation quality between cement sheath and salt layer. In addition, the irregular borehole in the salt layer and the expansion of well diameter make the displacement efficiency poor in the cementing process, which restricts the cementing quality of this kind of wells. At present, due to the unsatisfactory cementing quality and low excellent rate of cementing quality in the salt layer during the construction of Wen 23 gas storage, the construction of gas storage cannot be completed as planned. Therefore, in order to ensure the successful construction and service life of gas storage, the cementing technology research of big-thickness salt layer in Zhongyuan Gas Storage Group is carried out.The salt resistant fluid loss reducer and retarder are selected through the project test, and the expansion early strength agent and toughening agent are selected. Through the compatibility research and the evaluation of the performance of cement slurry and the cementation strength of cement stone by the erosion of different salt content, a fresh-water-salt-resistant and ductile cement slurry system suitable for salt rock cementing is formed; In terms of cementing technology, we have developed well hole optimization technology, optimized leakage prevention technology in salt section and supporting high-quality sealing technology in salt layer, formed cementing technology and recommended practices for Wen 23 gas storage, and effectively ensured the primary success rate of cementing in Wen 23 gas storage. The research results of this subject have been successfully applied in 12 wells of Wen 23 gas storage and Wei 11 gas storage. The qualified rate of cementing quality has been increased from 96% to 100% and the excellent rate has been increased from 12% to 83.33%, which meets the requirements of gas storage for salt layer sealing quality and ensures the safe and efficient operation of Zhongyuan Gas Storage Group.

The sealing integrity of cement sheath directly affects the service life of oil and gas wells, and plays an important role in oil well operation and production. In this paper, the evaluation of sealing integrity of cement sheath was divided into two parts: the integrity of formation and cement sheath, and the integrity of cement sheath and casing. Based on the convergence-constraint theory, the effect of convergence stress generated by formation on cement slurry during the hardening process was considered. And the evaluation method for casing-cement-formation sealing integrity was established. In addition, a quantitative relationship between compressive strength of cement sheath and formation characteristic parameters was proposed to determine the cement-formation sealing integrity. Besides, the integrity evaluation method of casing-cement-formation combination was verified by tensile strength, compressive strength and plastic zone of cement. The field application analysis showed that this method is valid to predict the cement failure. During the cementing operation, the integrity of casing-cement-formation interface can be controlled by adjusting the properties of the cement sheath.

A significant amount of research has been conducted on bentonite-acrylamide hydrogels. These gels are usually prepared by uniformly mixing bentonite with reactive monomers. Herein, a new preparation method of bentonite-acrylamide hydrogels has been proposed to cater to one novel application of bentonite-acrylamide hydrogels. In this method, bentonite-acrylamide hydrogel was obtained by pressing bentonite into a thin mud cake and extruding a mixed liquor of acrylamide, a cross-linking agent, an initiator, and water into the thin mud cake and then subjecting the system to water-bath curing. The effects of extrusion pressure, extrusion time, and acrylamide concentration on the tensile strength and elemental composition of bentonite-acrylamide hydrogel were investigated. The results show that the tensile strength of the bentonite-acrylamide hydrogel first increased and then tended to be stable with the further increase in extrusion pressure and extrusion time. As the concentration of acrylamide increased, the tensile strength of the bentonite-acrylamide hydrogel increased first and then decreased slightly. With the increase in extrusion pressure, extrusion time, and acrylamide concentration, the contents of C and N elements in the thin mud cake gradually increased and then tended to be stable, which reflects the state of the monomer entering the thin mud cake. In addition, the elemental composition of the bentonite-acrylamide hydrogel was analyzed via the scanning electron microscopy-energy dispersive X-ray spectrometry method, and it was found that the composition of the hydrogel was relatively uniform in the direction of mixed liquor extrusion.

One-part geopolymer similar to conventional Portland cement by just adding water is a new type of green cementitious material. Na2SiO3-anhydrous is an excellent powder activator for preparing one-part geopolymer, but its CO2-e emission and alkalinity are very high. In this study, the Na2CO3 was used to replace a portion of Na2SiO3-anhydrous, and the properties of one-part geopolymer with composite activators were investigated systematically. The possible influencing mechanism of the complex use of activators in one-part geopolymer was proposed. Test results indicate that the replacement level of Na2CO3 has slight impact on the fluidity and increases the final setting time significantly. This is directly related to the initial heat release rate and the type of network structures formed. The compressive strength decreases with increasing the Na2CO3 content. On the one hand, the quantity of gelatinous products reduces and calcite is produced as the new phase after replacing Na2SiO3-anhydrous by Na2CO3. On the other hand, the gathering of calcite and low-crystalline CaCO3 in some regions leads to the generation of many large micro-cracks, which explains the change in the porosity of the unfavorable pores. Judged from the cost per MPa and total CO2-e emission for a cubic meter of cementitious materials, one-part geopolymer activated by composite activators is cleaner than that activated by single Na2SiO3-anhydrous or Na2CO3. This study provides a guidance for preparing one-part geopolymer with lower alkalinity and potential environmental impact.

One-part geopolymeric binders which are considered as cleaner non-Portland cementitious materials are prepared by first mixing the aluminosilicate materials with the solid alkaline activators before adding water, which makes the mixing method of the geopolymer being the same as Portland cement. In this paper, sinking spherical beads (SSB) is introduced into the raw materials containing fly ash (CFA) and ground granulated blast furnace slag (GGBS) to synthesize a ternary one-part geopolymer. A systematic investigation of the effect of SSB on the geopolymer pastes and mortars is performed through measuring the fluidity, final setting time, compressive strength and flexural strength. It is found that SSB can significantly improve the fluidity and mechanical properties of geopolymer due to its high reactive effect and remarkable morphological effect. The action mechanism of SSB for improving the performance of the geopolymer was also dissected. It is interesting to note that SSB has little influence on the initial heat flow and increases the cumulative heat relating to the strength development. The changes in the formation of C-A-S H and N-A-S H gels after the introduction of SSB are well captured by the XRD and EDX analysis. It clearly appears that the N-A-S H gel with the optimal Na/Si ratio of 0.5 can be generated by optimizing the rational proportion of raw materials and alkaline activators. This study not only demonstrates the superiority of SSB in synthesizing a ternary one-part geopolymer, but also develops a method to design the novel non-Portland cement only by using industrial wastes.

Sodium silicate is widely used as a coagulation accelerator for oil-well cement. However, the existing experimental results show that the addition of sodium silicate can significantly delay the setting of cement paste with retarder. This study investigated the effects of addition of sodium silicate on the setting time of oil-well cement. For oil-well cement with no retarder, the addition of sodium silicate shortened the setting time. In contrast, for oil-well cement with retarder, the addition of sodium silicate prolonged the setting time and served as a type of retarder. Moreover, the mechanisms involved in retarding the hydration of cement by adding sodium silicate were also examined in detail by XRD, BET nitrogen adsorption, and total organic carbon analysis. The results show that the addition of sodium silicate delayed the hydration of tricalcium aluminate and thus prolonged the setting process of oil-well cement.

Poor zonal isolation due to microcracks in cement sheath is a common problem that affects oil and gas exploration and also impacts the environment. In this study, pH-sensitive superabsorbent polymers (SAPs) have been successfully synthesized through copolymerization of 2-(Dimethylamino)ethyl methacrylate (DMAEMA) and acryloyloxyethyltrimethyl ammonium chloride (DAC) to achieve self-healing of microcracks in cement sheath. The chemical structure of p(DMAEMA-co-DAC) SAP was characterized using Fourier transform infrared (FTIR) spectroscopy. Water absorption tests determined the effect of cross-linker dosage and DMAEMA/DAC molar ratio on their water absorption rate (WAR). pH-sensitive tests showed they absorbed considerable water in neutral and weak alkaline solutions but little water in strong alkaline solutions. In addition, the WARs were quite small in high concentration calcium chloride solutions. The WARs in distilled water reduced after they were processed in cement slurry filtrate (CSF) due to hydrolysis of ester groups and the crosslinking effect of Ca 2 + ions. Additionally, the SAP showed good compatibility with the cement slurry. It had little impact on the thickening time, rheological property, fluid loss, and early compressive strength of cement slurry/stone. Eventually, sealing pressure test results indicated the self-healing properties of p(DMAEMA-co-DAC) SAP-modified oil well cement. Using a 2 wt.% SAP addition, microcracks up to 166 μ m can be sealed.

The setting time of the cement containing retarder at high temperature is longer than that at low temperature, which is an abnormal phenomenon and is adverse to the safety of cementing operation. Several kinds of retarders were chosen to demonstrate the abnormal phenomenon and to select the retarder with the ability to eliminate the abnormal phenomenon. Tartaric acid was found to be the only retarder which did not show the abnormal phenomenon. Moreover, it could eliminate the abnormal phenomenon of the cement containing a copolymer retarder. In addition, tartaric acid may also eliminate the abnormal phenomenon in cement containing other retarders, and it may be used with other retarders together to develop a compound retarder without the phenomenon of slow setting at high temperature. The elimination mechanism of the abnormal phenomenon was studied by comparing the hydration products of the cement containing AMPS-IA with the cement containing tartaric acid using XRD. Based on the results, there was a reduction in the hydration rate difference of tetra calcium aluminoferrite (C4AF) between low and high temperatures after introducing tartaric acid, which could be the reason why tartaric acid could eliminate the abnormal phenomenon.

pH-sensitive water and oil dual-absorption material (WODAM) has been successfully synthesized through microemulsion polymerization. Firstly, microemulsions prepared with monomers were analyzed by p...

The heat evolution during the hydration of cement was examined by multiple calorimetric methods: isothermal, oscillating isothermal, as well as temperature scanning tests in the temperature range from 15 °C to 95 °C. The apparent activation energy (Ea) of several different types of cements were all found to decrease significantly with temperature. Type of additives and water to cement ratio had little influence on the temperature dependence of Ea. The correlation between Ea and temperature may be mathematically simplified to a step function, where Ea is a nonzero constant below a critical temperature (Tcr) and reduces to zero above that temperature. The proposed model of Ea was combined with a scale factor model to simulate the influence of curing temperature on the hydration kinetics of cement with significantly improved accuracy compared to an earlier model.

In this paper, sodium carbonate and calcium hydroxide instead of sodium hydroxide used as composite activators, and slag are applied to prepare one-part alkali-activated slag. Furthermore, the properties of the slag activated by sodium hydroxide are compared. The compressive strength, XRD, TGA, MIP, and SEM analysis of the two systems are performed. The results show that the one-part alkali-activated slag prepared from sodium carbonate and calcium hydroxide has a superior compressive strength against the slag activated by sodium hydroxide. It is also found that the hydration speed of the sodium hydroxide activated slag is faster, and thus the higher compressive strength of the one-part alkali-activated slag is not caused by the hydration speed. The hydration of one-part alkali-activated slag produces a certain amount of calcium carbonate, resulting in a lower porosity in comparison with the slag activated by sodium hydroxide, which may be the reason for the better compressive strength of one-part alkali-activated slag.

The research objectives in this paper are designed to develop one new type of retarder for calcium aluminate phosphate cement (CAPC) to extend the thickening time. Results show that due to the influence of sodium hexametaphosphate, many kinds of conventional Portland cement retarder lose the retarding function in CAPC. AMPS/IA copolymer could extend the thickening time obviously; however, the thickening curves show consistency fluctuations. Although, treated AMPS/IA copolymer could avoid the consistency fluctuation, right angle thickening property is weak. Due to the synergistic effect, the combination of treated AMPS/IA copolymer and borax is more suitable as the retarder for CAPC.

In this study, an environmentally friendly epoxy resin is mixed with ground-granulated blast furnace slag (GGBS) for use as a stabilizer to enhance mechanical performance and leaching resistance properties of marine sediments. Investigations of unconfined compressive strength, Young's modulus, hydraulic conductivity and leaching behavior tests were performed on stabilized samples in order to understand the effects of hybrid stabilizer on sediment properties. In addition, XRD, SEM, EDX and moisture content analyses were conducted to illustrate the leaching controlled mechanism of the resin. Test results show that the mechanical performance is sensitive to the dosage of resin. The stabilized sediment sample with 5% of resin gave the best strength as well as excellent Young's modulus. Furthermore, the leaching controlled effect of the resin led to the stabilization of hazardous elements. The maximum content of As, Cd, V and Cr leached from the stabilized samples was much lower than the respective contamination limits of EP PART 503. The core–shell structure and chain-like framework which formed in the stabilized sediment system after the addition of resin could control the connection between the water environment and inorganic soluble minerals effectively. This investigation provides further beneficial uses of alkali-activated GGBS materials in the field of geotechnical engineering.

The cement sheath seal integrity is crucial for a safe operation of underground gas storage. Owing to its creep characteristics, the salt formation squeezes the cement sheath, which may cause failure of the cement sheath’s seal integrity and pose risks to the safe operation of underground gas storage. In this study, the experimentally obtained salt rock creep law and finite-element software ABAQUS were used to verify the adaptability of the salt rock creep in ABAQUS. In addition, a model of casing–cement sheath formation combination under creep formation conditions was developed. The effects of the in-situ stress (ISS) and cement sheath’s elastic parameters on the seal integrity of the cement sheath were studied in the salt rock layer. The creep of the salt rock increased the stress acting on the cement sheath over time and caused shear failure of the cement sheath. A larger uniform horizontal ISS led to a shorter time period for shear failure of the cement sheath, larger equivalent plastic strain (PEEQ), and larger yield area. A larger maximum horizontal ISS led to a shorter time period for shear failure of the cement sheath, larger PEEQ, and larger yield area. The yield area was concentrated in the direction of the maximum and minimum horizontal ISSs. Uniform and non-uniform horizontal ISS creeps did not cause tensile failure of the cement sheath. The reduction in the elastic modulus of the cement sheath and increase in the Poisson’s ratio of the cement sheath could reduce the shear failure risk of the cement sheath in salt rock formation. The influences of the ISS and cement sheath elastic parameters in the salt rock layer on the seal integrity of the cement sheath obtained in this study can provide references for the seal integrity failure of the cement sheath in the creep formation.

During the development of deep-water oil and gas resources, severe engineering problems or even marine geological hazards might be induced by the complex geological characteristics of deep-water weakly consolidated (DWC) formation. To solve these problems, the power-law cementing fluid was used to solidify the DWC formation during the well-cementing operation. However, the transportation process of cementing fluid in DWC formation is still unclear. To guide the solidification operation of DWC formation, a mathematical model for predicting the penetration distance of cementing fluid in DWC formation was proposed based on the generalized Darcy’s law and fractal theory. All the parameters in this model have clear physical meaning and no empirical parameter is involved. The numerical and experimental validation results show that the proposed model calculated penetration distance agrees well with both simulated and experimental results. The model capacity relates to the penetration pressure, the viscosity of cementing fluid, the permeability of formation, the effective radius of the flow path and the fractal dimension of formation. The maximum error of this model is less than 20%, which indicates that the mathematical model is reliable.

Inhibiting natural gas hydrate (NGH) decomposition is a crucial challenge in NGH strata cementation. Lecithin can inhibit the decomposition of NGH, however, before lecithin is added to oil well cement to create a cement slurry system that inhibits NGH decomposition, the effects of lecithin on the mechanical properties of oil well cement must be considered. Therefore, in this research, the effects of lecithin on the mechanical properties of oil well cement were studied. The elastic modulus and compressive strength were measured to evaluate the mechanical properties. The changes in the mechanical properties of cement with different lecithin concentrations were experimentally studied. Through experimental research and inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis, it was confirmed that a 1.5% lecithin concentration in the cement slurry inhibits NGH decomposition. Quantitative calculations determined the ratio of lecithin to calcium silicate hydrate (CSH) gel in an atomic model when the lecithin concentration was 0, 0.5%, 0.8%, 1.0%, 1.2% and 1.5%, and the lecithin–CSH gel atomic model was established with different concentrations. According to molecular dynamics simulations and experimental analyses, the influence mechanism of lecithin on the mechanical properties of cement was revealed. The experimental and simulation results demonstrated that as the lecithin concentration increased, the elastic modulus and compressive strength of cement decreased, and the interfacial adsorption energy between lecithin and CSH gel increased. The decalcification of CSH gel by lecithin and the migration of calcium to the surface result in decreases in the elastic modulus and compressive strength of cement. The mechanical properties of cement can be enhanced by increasing the calcium content and reducing the number of calcium migration channels of calcium. Finally, we evaluated the impact of lecithin on the rheological properties and setting time of cement slurry. The research results are significant for the further development of cement slurry systems with NGH decomposition resistance.

This paper investigated the suitability of xanthan gum as a thixotropic agent utilized in high-temperature natural gas well cementation. The konjac gum and KCl are used to synthesize a novel thixotropic agent and keep the thixotropic property of xanthan gum at high temperatures. The increment of consistency method are used to evaluate the thixotropic performance of the cement. Compressive strength tests, scanning electron microscope, and X-ray diffraction analysis are performed to study the effects of the thixotropic agent on the properties of cement at high temperatures. Moreover, the thixotropic mechanism is revealed, as well. Test results show that the high-temperature resistance property of xanthan gum is limited. The konjac gum and KCl should be used to enhance the thermal stability of xanthan gum to achieve better thixotropic property at high temperatures. The thixotropic agent does not influence the hydration products but slows down the hydration process of cement. Even though the thixotropic agent influences the microstructure of cement, the compressive strength still meets the sealing requirements of natural gas wells. The K+ ions in KCl connect the molecular chains in xanthan gum through the salt bridge effect, which inhibits the transformation of xanthan gum's double helix structure and enhances the thermal stability of the molecular structure. Furthermore, the acetyl groups in konjac gum generate hydrogen bonds with pyruvate groups in xanthan gum. This effect makes the composite structure more stable and finally results in a thermal stable thixotropic agent. The proposed novel three components thixotropic agent is an effective solution to solve the gas migration issue in high-temperature natural gas wells.

The core-shell oil absorption material (OAM) with fumed silica shell was achieved from Pickering polymerization. The modified fumed silica wall could well stabilize both Pickering emulsion and Pickering polymerization. The particle size of encapsulated OAMs decreased with the increasing concentration of fumed silica and remained unchanged when the concentration was more than 1 wt.%. This fumed silica shell had little effect on the oil absorption rate of OAM. The importance was that the shell reversed the surface property and improved the alkali resistance of OAM. We believe that our core-shell OAMs could reach the self-healing ability of the oil well cement.

This research work was carried out to evaluate the properties of oil well cement with high dosage of metakaolin. The fresh pastes were made using an initial water/solid ratio of 0.5 by weight and then hydrated for periods up to 56 days. The mechanical performance was assessed from compressive strength. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied in order to study the hydration products and qualitative of microstructure. Feasibility as oil well cement of metakaolin replaced cement was assessed by thickening time, corrosive fluid exposure, density and rheology test. Test results confirmed that the early-term strength decreased with the increasing metakaolin content and the set cement with more metakaolin showed higher long-term strength at 75 °C. The cement pastes with 40–60%wt metakaolin presented good strength both in early-term and long-term curing at 150 °C and above. The metakaolin replaced cement pastes demonstrated low porosity and good strength due to stable hydration products and dense microstructure. Meanwhile, the filling effect of metakaolin partials reduced porosity and improved corrosion resistance of hardened pastes. The MK replaced cement pastes are applicative for the cementation of deep wells, acid rich wells and geothermal wells.

In this paper, the effects of formation water on the construction quality of the cement-formation interface under static and water disturbance conditions were studied. The critical flow velocity of formation water that affects the construction quality was revealed. A flow velocity prediction model was established to provide a reference for the wellbore shut-in range of surrounding injection wells during the cementing operation. The test results and mathematical analysis show that the construction quality of annulus cores cured by formation water display no adverse effect when compared to that of the distilled-water-cured samples under static conditions. A flow velocity of 12 mL/h is the critical flow velocity of formation-water-cured samples under water disturbance conditions. The failure of the cement-formation interface with water disturbance results from the Ca2+ loss of the cement matrix. The flow rate and the composition of formation water show a synergistic effect on the failure of the cement-formation interface. This study is essential to improving the construction quality of clastic rock formations, which contain abundant formation water.

This research work designed a novel mud-cake solidification method to improve the zonal isolation of oil and gas wells. The calculation methodology of mud-cake compressive strength was proposed. The optimal formula of activator and solid precursors, the proper activating time and the best activator concentration were determined by the compressive strength test. The effects of solid precursors on the properties of drilling fluid were evaluated. Test results show that the respective percentage of bentonite, metakaolin, slag and activator is 1 : 1 : 0.3 : 0.8, as well as the optimum ratio of Na 2 SiO 3 /NaOH is 40 : 1. The optimum concentration of activator is 0.21 and the activating time should be more than 10 min. The solid precursors did not show any bad influence on the rheological property of drilling fluids. Even though the compressive strength decreased when the solid precursors blended with barite, the strength values can still achieve 8 MPa. The reaction of metakaolin and activator formed cross-link structure in the mud-cake matrix, which enhanced the connection of the loose bentonite particles, lead to the significant enhancement of shear bonding strength and hydraulic bonding strength. This mud-cake solidification method provides a new approach to improve the quality of zonal isolation.

The integrity of cement ring is critical for the safe production of crude oil and natural gas and the protection of marine environment in deep water shallow formation. Due to the poor support of the shallow formation to the cement ring, the cement ring is easily damaged by the casing internal pressure (CIP). Based on extended finite element method (XFEM), the effect of CIP on the integrity of cement ring was investigated in this paper. A casing-cement-formation (CCF) combination model was established. Under different structure and mechanical properties of the cement ring, and different mechanical properties of the shallow formation, the maximum casing internal pressure (MCIP) when cement ring was broken was studied. This paper is of great significance to study the failure mechanism of cement ring integrity in deep water shallow formation, and has guidance for proposing corresponding rationalization suggestions and measures.

The retarding side effect and the compatibility with other additives are the main problems that limit the field application of the synthesized fluid loss control additive (FLCA). The effect of the type and content of carboxylic acid groups on the retarding side effect of FLCA and the compatibility between FLCA and the retarder AMPS-IA synthesized using 2-acrylamido-2-methyl propane sulfonic acid (AMPS) and itaconic acid (IA) was studied in this paper. The type and content of carboxylic acid group have a great influence on the fluid loss control ability, the compatibility with retarder and the retarding side effect of FLCA. FLCA containing IA or maleic acid (MA) shows better compatibility with retarder than FLCA containing acrylic acid, but the retarding side effect of FLCA containing MA is weaker than that of FLCA containing IA. Thus, MA is the most suitable monomer for synthesizing FLCA having good compatibility with retarder AMPS-IA.

In the study of drilling dynamics, many investigations are limited to laboratory systems and simple mathematical models. Using field measurement data and a new dynamical model in a rotary steerable drilling system, we demonstrate the existence of low-dimensional chaos in drilling. The behaviors of the mathematical model and actual measurement are shown to be consistent. The revealing of chaos provides a new way to detect early fatigue cracks as weak signals in a noisy environment to reduce engineering cost and the possibility of disaster.

Aiming at the abnormal phenomenon of the setting time of the cement slurry with retarder at around 85 °C surpassing the low temperature, the effect of retarder dosage, the dosage of extra lime (CaO), the mixing mode of the extra lime (CaO), and the precuring of the cement slurry at high temperature on the setting time of cement slurry were studied. The setting time of the cement slurry without the retarder changed a little as the increase of the dosage of the extra lime while the setting time of cement slurry with the retarder shortened obviously. The free lime contained in the cement itself had a great influence on the setting time of the cement slurry with the retarder. The content drop of the Ca(OH)2 in the cement slurry induced by the reaction acceleration between C4AF and Ca(OH)2 was responsible for the abnormal phenomenon.