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Abstract In a bid to combat fluid loss in muds where the effects of high downhole temperatures have pronounced effects on conventional fluid loss additives, several materials have over time been evaluated. One of such materials is the multiwalled carbon nanotubes (MWCNTs). Most studies in the literature limit the scope of their investigation to how the MWCNT affects mud rheology when added in minute concentrations (0.01–1 ppb). In this study, however, the performance of high concentrations (0.5–3 ppb) of multiwall carbon nanotubes as fluid loss control additives in field-applicable mud systems was put to the test. The essence was to establish an optimal concentration useful for field applications. The degree to which the introduction of varying concentrations of the MWCNT altered the muds capacity to control filter loss was the cardinal areas evaluated. The following are the major outcomes of the experimental study: The plastic viscosity, the yield point and the gel strengths showed a progressive increase as the concentration of the MWCNT in the mud increased for both the water- and oil-based muds. However, an optimum concentration of 2 ppb was observed for the water-based mud. For the filter loss tests on the oil-based mud, the results indicate that low concentrations (0.5 ppb) of the MWCNT led to high filter loss volumes (15 ml), but an increase up to 2.5 ppb reduced the margin of the filter loss volume by 52% (7 ml) from the initial value and a 50% decrease for the standard case. In the case of the water-based mud, equivalent amounts of MWCNT recorded less fluid loss than the standard. A moderately hard and firm cake was reported for all concentrations of the standard and MWCNT for the water- and oil-based muds; however, their cake thickness values were 2 mm and 1 mm for the water- and the oil-based muds, respectively.

Additives to drilling fluids and oil well cements play a significant role during wellbore drilling operations. These additives (such as carboxymethyl cellulose and starch) are often expensive and most times degrade at high temperature conditions. Although seashells (usually considered waste materials) have been utilized for various purposes in drilling muds as weighting agents and lost circulation materials, however, to the best of our knowledge, there is no research conducted yet to test their feasibility and performance as retarders or accelerators in oil well cements. In addition, no study has compared the filter loss capabilities of these seashells as drilling mud additives. Filling this gap is what makes this work novel and is the major contribution of this work to the extant literature on this subject. The specific objective of this work is to bring to light how useful seashells could be as a drilling mud and oil well cement additive from an experimental standpoint. To this end, the capability of the pulverized and calcined shells of egg, snail, oyster and periwinkle as mud filter loss control agents and as oil well cement additives were evaluated. Thirteen water based mud samples and one oil well cement sample were formulated with the shells as additives. The basic tests run on the formulated mud and cement samples were the filter loss test (using the American Petroleum Institute filter press) and cement setting time tests (using the Vicat’s apparatus) for the mud and cement respectively. The conventional filter loss control material - carboxymethyl cellulose (CMC) was used as the control. Results from the filtration tests showed that the filter loss capability of the shells decreased from egg shell to snail shell to periwinkle shell. With respect to cement, incorporation of calcined oyster and periwinkle seashells resulted in extended final setting times of the cement. In quantitative terms, it was observed that the final setting time of the cement was extended by an average of 14 and 28 ​min as the amount of oyster and periwinkle shell respectively introduced to the cement was increased from 5 to 15%. Conclusions drawn are that both the oyster shell powder and the periwinkle shell powder act as retarders. It is concluded that the filtration property of the seashells had a direct relationship with the amount of the seashell added. Economically, the pulverized seashells have comparable cost performance with the conventional filter loss and cement retarder additives. By utilizing these waste shells in this way, the overall well drilling cost would be reduced and the environment would be protected.

In a bid to combat fluid loss in muds where the effects of high downhole temperatures have pronounced effects on conventional fluid loss additives, several materials have over time been evaluated. One of such materials is the multiwalled carbon nanotubes (MWCNTs). Most studies in the literature limit the scope of their investigation to how the MWCNT affects mud rheology when added in minute concentrations (0.01–1 ppb). In this study, however, the performance of high concentrations (0.5–3 ppb) of multiwall carbon nanotubes as fluid loss control additives in field-applicable mud systems was put to the test. The essence was to establish an optimal concentration useful for field applications. The degree to which the introduction of varying concentrations of the MWCNT altered the muds capacity to control filter loss was the cardinal areas evaluated. The following are the major outcomes of the experimental study: The plastic viscosity, the yield point and the gel strengths showed a progressive increase as the concentration of the MWCNT in the mud increased for both the water- and oil-based muds. However, an optimum concentration of 2 ppb was observed for the water-based mud. For the filter loss tests on the oil-based mud, the results indicate that low concentrations (0.5 ppb) of the MWCNT led to high filter loss volumes (15 ml), but an increase up to 2.5 ppb reduced the margin of the filter loss volume by 52% (7 ml) from the initial value and a 50% decrease for the standard case. In the case of the water-based mud, equivalent amounts of MWCNT recorded less fluid loss than the standard. A moderately hard and firm cake was reported for all concentrations of the standard and MWCNT for the water- and oil-based muds; however, their cake thickness values were 2 mm and 1 mm for the water- and the oil-based muds, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Carbon-based nano-materials and polymers are the most propitious materials proposed to cure the serious problems encountered in drilling operation. The aim of this study is to improve the essential properties of selected water-based drilling muds (WBMs) using a new synthesized complex of oxidized multi-walled carbon nanotube wrapped by polyethylene glycol (POCNT). A rotational rheometer and an API filter press were used to analyze the rheological and filtration properties of the drilling muds, and smart hydrophilic and hydrophobic behaviors were expected due to carboxylic bonds and PEG polymer chains. It has been shown that adding a relatively low amount of POCNT to selected water-based muds will lead to a significant improvement in rheological behaviors of the drilling fluid, and a noticeable reduction in their associated formation damage. Specifically, the presence of POCNT in WBMs has shown to enhance the viscosity, yield stress, and subsequently the carrying capacity of the drilling muds at several temperatures. Moreover, it has been indicated that this formulation could properly decrease the permeability of mud cake, and as a result, reduce the filtration volume of nanofluids compared with that of base fluid by up to 82%. At the end, the curve fitting analysis proves that the Herschel- Bulkley method better fits the rheological behaviors of this new nano drilling fluid. [ABSTRACT FROM AUTHOR]

The need for converting waste to wealth triggered the zeal to undertake this work. This study focused on cellulosic agro waste materials that have the potential to control filtration loss in drilling muds. There was a wide spectrum from which to choose from – from the obvious to the complex. The choice of these materials was based on the characterization of each of them from published literature but was narrowed down to the ones available in Nigeria. From the review, it was observed that a good number of researchers have been diligently studying the use of agro-waste materials as filter loss control additives in drilling muds. The inclination of most of the research studies have been towards assessing the potential of using the cellulosic agro waste materials as fluid loss control additives and then comparing their rheological and filter loss characteristics with the conventional fluid loss control additives. The available studies by various researchers on this subject have been compiled from 1997 to 2017 and the findings of each researcher is highlighted. A summary of the findings indicate that the agro waste materials were historically used as lost circulation materials, and that a mixture of two or more agro waste materials prevents lost circulation better than when used alone. However, this review further show that agro waste materials are ubiquitous and inexpensive and could equally serve as filter loss control agents in drilling muds. Thus, their utilization as filter loss control agents in drilling muds help reduce environmental pollution and ultimately reduce drilling fluid costs. From an economic perspective, this work indicates that all the agro waste materials were cost effective even after processing compared to the conventional fluid loss control materials such as carboxymethyl cellulose and polyanionic cellulose. In this respect, saw dust and corn cob were found to be the cheapest and most expensive agro waste materials respectively. This work also highlighted some gaps in the literature which should be filled. These gaps include but are not limited to: microscopic structure analysis and filter cake properties description of the muds formulated with agro waste materials. [ABSTRACT FROM AUTHOR]

In this study, synthetic sulfonated polymers were used in order to enhance the rheological properties of drilling fluids. The capability of these polymers in reducing the effects of environmentally friendly, but harmful, pollutants such as cement, calcium chloride, gypsum as well as pH changes were investigated. In the present work, two sulfonated synthetic polymers, namely Polythin and Polydrill, which are considered to be environmentally friendly polymers, were used. Polydrill controls the fluid loss and is resistant to high temperatures and also pollutants. The injection of this polymer into drilling fluid slightly increases the viscosity levels. Polythin prevents the precipitation of bentonite at high temperatures and facilitates fluid pumping by reducing its rheological and static shear strength. Polythin polymer also prevents the formation of bentonite gelation (precipitation of bentonite) at higher temperatures and is stable up to 260 °C. This polymer is also capable of completing the effects of fluid loss additives and reduction of filtration in HTHP drilling fluids. Furthermore, this polymer reduces rheology, strength, and static shearing values and facilitates pumping of the drilling fluid. The combination of aforementioned polymers improves the thermal resistance of drilling muds while maintaining the rheology and reducing the amount of filtrate for HTHP drilling fluids. In these experiments, the rheological properties of the fluid including apparent viscosity (AV), plastic viscosity (PV), yielding point (YP), gelation resistance or gel strength (GEL), fluid loss (FL), and the pH of the fluid were studied before and after the addition of the pollutants. The results indicate that certain proportions of these two polymers increase the rheological properties of drilling fluids and can significantly change the weight percentages of pollutants. It is also notable that the rheological properties were normally constant. However, in some cases, smaller values of rheological parameters enhanced the efficiency in the presence of pollutants. In the case of calcium chloride, rheological parameters (AV, PV, YP, and gel strength) are almost constant, while fluid loss greatly increases.

In the fiber-to-the-home era, thousands of optical fibers will have to be accommodated in the central offices of optical access networks. To reduce maintenance costs and improve the service reliability of optical fiber networks, the authors must develop an optical fiber line testing system with a function for in-service line monitoring that uses a test light with a wavelength different from the communication light wavelength. To monitor an in-service line in an optical network, the effective rejection ratio of the test light must be taken into account. This ratio depends on the spectrum of the test light from the optical time-domain reflectometer and the rejection band of the filter in front of the optical network unit. The dependence of the effective rejection ratio as a function of the sideband suppression ratio (SBSR) and of the ratio of the rejection band to the bandwidth of the sideband noise d/D is clarified. When d/D=0.1 and the target effective rejection ratio of the filter is -40 dB, the SBSR and the filter loss of the termination cable must be -70 and -43 dB, respectively, or the SBSR must be -80 dB. When d/D<0.5 and the target effective rejection ratio of the filter is -40 dB, the SBSR is also required to be -80 dB. In-service line monitoring for a 10-Gb/s transmission using a 1650-nm test light with an SBSR of -80 dB is also demonstrated. [ABSTRACT FROM PUBLISHER]

Optically preamplified receiver performance according to the vestigial sideband (VSB) filtering has been numerically investigated for 40-Gb/s optical signals modulated with nonreturn-to-zero, duobinary nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed RZ, and duobinary carrier-suppressed RZ formats. The VSB filtering enables the spectral widths of NRZ, duobinary NRZ, and RZ signals to be reduced without severe power penalties at the receiver. On the other hand, carrier-suppressed RZ and duobinary carrier-suppressed RZ signals have no large advantages over VSB filtering because of the characteristics of their signals. Our results suggest that RZ signals are the most suitable modulation format for VSB filtering, without considering the filter loss, because of the tolerance of the intersymbol interference and a large spectral width. However, duobinary NRZ signals are the most suitable modulation format for VSB filtering, considering the filter loss, because of their narrow spectral width. [ABSTRACT FROM PUBLISHER]

Adding nanoparticles in a drilling fluid can aid in the sealing of the nanopores in the borehole wall rock and the mud cake; in this way, the filtrate loss of the drilling fluid can be reduced and the borehole wall is stabilized. In this work, the spectrophotometric method was used to study the effect of dispersants on calcium carbonate nanoparticles. The best dispersion effect was achieved at cetyltrimethyl ammonium bromide (CTAB) concentration of 4 wt%, dispersing time of 45 min, pH value of 8 and stirring speed of 900 rpm. The structure analysis showed that the adsorption layer was formed on the surface of calcium carbonate nanoparticles after CTAB modification, and no new crystalline compounds appeared. Under these optimized dispersing conditions, aggregation was prevented as manifested by the dramatically decreased average particle size of calcium carbonate nanoparticles while the surface hydrophilicity and Zeta potential of calcium carbonate nanoparticles both increased. Furthermore, we showed that a drilling fluid incorporating such well dispersed calcium carbonate nanoparticles exhibit decreased filter loss and thus better performance in sealing compared to the calcium carbonate nanoparticles without dispersants., (© 2021 IOP Publishing Ltd.)

We investigated the performance of viscoelastic surfactant (VES) solution when applied in treatment on the uninvaded matrix using core flooding tests to analyze the impact of VES/CaCl2 concentration on fluid viscosity. In this paper, core samples from Tahe carbonate reservoir, with an average permeability less than 0.02 × 10−3 μm−2 and a small average porosity in the range of approximately 0.04–5.24% are used in the experiments. Computed tomography (CT) scanning is used to provide a detailed description of inner structure variation of cores after the acid system treatment. The results confirmed that a large pressure difference contributed to fracture propagation and the relative permeability of water increased significantly after the treatment. It was also found that higher concentrations of VES and/or Ca2+ induced higher viscosity and a stronger fracturing effect, while a lower concentration improved the reaction rates and etching effect, generating small worm holes inside the core. Foam in-situ produced during the etching process is the major contributor to the fluid viscosity enhancement. The permeability of fracture formed on the surface of the core is more sensitive to the confining pressure. These findings can help better understand the rheological properties of the acid system and etching and fracturing mechanisms during acid treatment, and which provides instructions for field implementation. [ABSTRACT FROM AUTHOR]