High-performance Water-based Drilling Fluid Research Articles

Performance evaluation of trimethylolpropane ester as high-temperature resistant lubricant for high performance water-based drilling fluids

As drilling operations increasingly target large-displacement wells, horizontal wells, deep wells, and ultra-deep wells, the challenges of excessive drilling resistance and downhole safety have become more prominent. During the drilling process, one of the primary technical methods for preventing and addressing drilling safety issues is the reduction of downhole frictional resistance through the addition of lubricants to the drilling fluid. In this study, a high-temperature and high-salt-resistant drilling fluid lubricant was synthesized using raw materials such as oleic acid and trimethylolpropane. The lubricant exhibited excellent lubrication performance under high-temperature and high-salt conditions. When added at a 1.5% dosage to a 4% freshwater-based slurry, HZ-1 resulted in a 95.2% reduction in the lubrication coefficient. After aging at 200 °C, the HZ-1-containing slurry maintained an 87.9% reduction, and when used with a NaCl dosage of 36%, the slurry still exhibited an 80.5% reduction. Furthermore, HZ-1 exhibited favorable compatibility with both polymer drilling fluid and polysulfone drilling fluid systems. It had basically no effect on the rheological properties of the drilling fluid and reduced filtration loss. Moreover, HZ-1 exhibited a lubrication coefficient reduction rate of 94.5% in freshwater-based slurry and 85.5% in brine-based slurry, outperforming domestic and foreign lubricants. It outperformed these comparative lubricants in terms of lubrication and drag reduction within the same period. The analysis of the lubrication and drag-reduction mechanism revealed that HZ-1, when adsorbed onto a metal surface, formed a hydrophobic and high-strength physical adsorption film. This film prevented direct contact between drilling tools and the friction surface of the well wall, resulting in a significant reduction in the lubrication coefficient. Furthermore, using the drilling fluid system containing HZ-1 lubricant, the wear scar diameter formed on the surface of the four-ball friction experimental body was the smallest, measuring only 0.78 mm. This property significantly enhances the extreme-pressure and anti-wear performance of the friction sub-surface. Consequently, HZ-1 effectively prevents complications such as pressure support, stuck drilling, and high frictional resistance, thereby significantly reducing costs and improving efficiency.

Experimental Investigation and Computational Insights of Enhanced Rheological Stability of Water-Based Drilling Fluids by Microspherical Polymers

Summary 3D bulk polymer, as an alternative to linear polymer, has exhibited large potential in formulating high-performance water-based drilling fluids. Understanding the mechanism behind the enhanced rheological stability of drilling fluids by microspherical polymers is critical for designing and developing new high-performance drilling fluids. In this work, we conducted a pioneering investigation that integrated experimental techniques with computational modeling, to explore the enhancement mechanism involved in the targeted drilling fluids. Inverse emulsion polymerization experiments were first carried out to fabricate the microspherical polymer acrylic acid (AA), acrylamide (AM), and 2-acryloylamino-2-methyl-1-propanesulfonic acid [P(AA-AM-AMPS)], and then physicochemical properties of microspherical polymer were characterized. Subsequently, the performance of drilling fluids with microspherical polymer as an additive was systematically evaluated. Finally, molecular simulations were used to investigate the characteristics of chemical active sites, molecular conformation, and structural variation at various temperatures. The results showed that the final microspherical polymer has a core-shell structure, with an average size of 198.3 nm and a molecular weight of 6.2×106 g/mol. The 3D structure exhibits good thermal stability, and thermal decomposition occurs above 220°C. The drilling fluids formulated with the microspherical polymer showed better rheological stability in the medium-low (4–65°C) and medium-ultrahigh (40–240°C) temperature ranges, compared with the relevant drilling fluids with the parallel linear polymer. Analyses on electrostatic potentials (ESPs) and frontier molecular orbital (FMO) revealed that active groups within the confined sphere domain mainly include carbonyl C = O and amide -CO(NH2). Additionally, these active groups exhibit a hierarchical distribution in the outer molecular region. Analyses on the radius of gyration (Rg) and the radial distribution function g(r) further validated the core-shell structure of microspherical polymer and its temperature-resistant stability. Moreover, a new self-consistent structural compensation model was proposed to rationalize the structure-activity relationship of microspherical polymer in drilling fluids. The computational results align well with the experimental findings. This pioneering work will provide valuable information for both the synthesis of new functional additives and the formulation of tailored-performance drilling fluids.

Development of a dual-functional inhibitor for natural gas hydrates and construction of drilling fluid system

Throughout the 21st century, natural gas hydrates have emerged as a pivotal and promising clean energy resource with immense potential for commercial development. However, during shallow-water gas hydrate drilling in deep-sea areas, heat and mass transfer between the drilling fluid and the natural gas hydrate reservoir result in hydrate dissociation. As a result, the reservoir strength is weakened, wellbore instability occurs, and there is a high risk of well collapse. Additionally, the formation of secondary hydrates can cause blockages in drilling tools or pipelines, compromising drilling safety. In this study, acrylamide and dimethyl diallyl ammonium chloride were used as raw materials to successfully develop a dual-effect hydrate inhibitor named ADP. The results showed that a 1% ADP concentration increased the inhibition efficiency of hydrate dissociation by approximately 21.13%. Furthermore, core immersion and linear expansion experiments using a 1% ADP solution showed that after 24 h, the core maintained its structural integrity without experiencing collapse, and the linear expansion rate decreased to 1.5%. Building upon the HEM system, this research employed the developed dual-effect hydrate inhibitor as the core component and further optimized density, rheology, filtration loss, hydration expansion inhibition, and hydrate inhibition properties to construct a high-performance water-based drilling fluid system for strong hydrate inhibition. Performance evaluation of the HTX system demonstrated excellent rheological filtration, lubrication, plugging, hydration expansion inhibition, and hydrate inhibition properties. Additionally, predictive models for drilling fluid rheological parameters under different temperature conditions were established. The research outcomes presented in this paper hold significant practical value in addressing the wellbore stability issues encountered during the drilling process of gas hydrate reservoirs in deep-sea areas.

Structure-activity relationships for hydration inhibition and environmental protection with modified branched polyethyleneimine: Experiments and simulations

Inhibiting the surface hydration of clay is the main task for the water-based drilling fluids used in the development of shale gas. Branching polyethyleneimine (BPEI) completely inhibits the clay surface hydration. However, the use of BPEI is limited by its high toxicity. In this paper, BPEI was modified by grafting with hydroxyethyl groups to reduce the toxicities of BPEI hydration inhibitors. The structures and properties of the modified BPEI were characterized by infrared spectroscopy, mass spectrometry, the luminescent bacteria method, isothermal adsorption, X-ray diffraction, thermogravimetric analysis, contact angle measurement, scanning electron microscopy, X-ray photoelectron spectroscopy and molecular simulations. The relative luminescence rate of the modified BPEI inhibitors increased from 14 % to 62 % with increases in the number of grafted hydroxyethyl groups. After hydrated sodium montmorillonite (Na–Mt) contacted the modified BPEI inhibitors, the basal spacings of the Na–Mt decreased from 1.90 nm to a minimum of 1.40 nm, and the DTG curve had only one low-temperature peak. Molecular simulations showed that the energy for adsorption of the inhibitor on the Mt surface increased with increases in the number of grafted hydroxyethyl groups. These results suggested a structure-activity relationship for inhibition and the biological toxicity of the modified BPEI inhibitor. That is, within the range of 20:1 to 5:1 for the molar ratios of amino and hydroxyl groups, increases in the number of grafted hydroxyethyl groups gradually decreased the biological toxicities of BPEI inhibitors, and the inhibition performance was gradually enhanced. BPEI-OH4 (amino:hydroxyl = 5:1) showed the best performance among the modified BPEI inhibitors. This provides an excellent inhibitor and a low-toxicity modification method, which will facilitate the development of environmentally friendly high-performance water-based drilling fluids.

Inhibition mechanism of cationic polyacrylamide on montmorillonite surface hydration: A molecular dynamics simulation study

Cationic polyacrylamide (CPAM), a typical drilling fluid shale inhibitor can prevent the clay swelling and maintain the wellbore stable. Understanding the adsorption behavior of CPAM on montmorillonite (MMT) surfaces is of great significance in explaining the excellent performance of cationic inhibitors. In this work, molecular dynamic simulations (MD) are applied to investigate the adsorption mechanism of CPAM on the Na-MMT surface. The simulation results show that there are two main adsorption configurations of CPAM: 1) trimethylamine group adsorption; 2) the co-adsorption of trimethylamine group and amide group, the latter has stronger interaction energy, also trimethylamine group accounted for a large proportion of the interaction energy. The CPAM coating will decrease the H-bond number, neutralize the negative charge of Na-MMT surface and weaken the surface hydration ability of Na-MMT. Due to the existence of the CPAM coating, the diffusion and transport ability of water molecules on Na-MMT surface are greatly reduced. This study provides a theoretical explanation for the coating-forming mechanism and adsorption characteristics of CPAM inhibitors on Na-MMT surfaces and may shed light on the design of high-performance water-based drilling fluid systems.

A new environmentally friendly water-based drilling fluids with laponite nanoparticles and polysaccharide/polypeptide derivatives

Considering the increasing environmental pressure, environmentally friendly and high-performance water-based drilling fluids (WBDFs) have been widely studied in recent years to replace the commonly used oil-based drilling fluids (OBDFs). However, few of these drilling fluids are entirely composed of natural materials, which makes it difficult to achieve real environmental protection. Using laponite nanoparticles and various derivatives of natural materials, including crosslinked starch, cellulose composite, gelatin ammonium salt, poly-l-arginine, and polyanionic cellulose, a kind of environmentally friendly water-based drilling fluid (EF-WBDF) was built for drilling in environment-sensitive areas. The properties of this EF-WBDF were evaluated by thermal stability tests on rheology, filtration, inhibition, and salt contamination. Besides, biological toxicity, biodegradability, heavy mental content and wheat cultivation tests were conducted to investigate the environmental factor of EF-WBDF. Results showed that EF-WBDF displayed satisfactory thermal resistance up to 150 °C, and the rheological properties did not suffer significant fluctuation, showing potential application in high-temperature wells. The optimal rheological model of EF-WBDF was Herschel–Bulkley model. This EF-WBDF performed an eligible filtration of 14.2 mL at 150 °C and a differential pressure of 3.5 MPa. This fluid could still maintain colloidal stability after being contaminated by 7.5% NaCl or 0.5% CaCl 2 . Meanwhile, rather low clay swelling degree of 2.44 mm and high shale recovery of more than 95% ensured the inhibitive capability of EF-WBDF. Furthermore, EF-WBDF presented a half maximal effective concentration (EC 50 ) of 51200 mg/L and a BOD/COD ratio of 47.55%, suggesting that EF-WBDF was non-toxic and easily biodegradable. The wheat cultivated in EF-WBDF could grow healthily, beneficial for reducing the adverse impact on ecological environment. The formed EF-WBDF has a promising future for drilling in environment-sensitive and high-temperature areas.

Novel approach to improve shale stability using super-amphiphobic nanoscale materials in water-based drilling fluids and its field application

Abstract In this study, super-amphiphobic nano-silica nanoparticles (SA-NPs) were used to enhance the shale stabilization performance of water-based drilling fluids (WBDFs) by altering the surface wettability, preventing the capillary self-priming effect, and plugging the nano-micro pores of shale. The results of transmission electron microscopy, particle size distribution, and scanning electron microscopy characterization revealed that SA-NPs exhibited a nanoscale “coalesce” structure, which is composed of spherical particles joined together, and could form a nano-papillary structure on the shale surface. Due to the presence of nano-micro scale rough structures and ultra-low surface energy components, the shale treated by SA-NPS exhibited super-amphiphobic surface property in the contact angle test. Contact angles of water and hexadecane on the shale surface reached up to 154.13° and 151.34° after being treated with SA-NPs, respectively. Furthermore, the addition of 1% SA-NPs in WBDFs could reduce the linear swelling rate from 40.5 to 6.0%, increase the shale cuttings recovery percentages from 82.5 to 95.6%, increase the plugging rate of low permeability shale core from 81.25 to 94.00%, and raise the high-temperature and high-pressure uniaxial compressive strength from 3.45 to 4.87 MPa. Compared with the polyether amine and fumed nano-silica, the addition of SA-NPs produced the best performance. Based on the excellent shale stabilization performance of SA-NPs, a high-performance WBDF was developed and applied in Dagang Oilfield. During the drilling operation， no wellbore instability, sticking, and other complex situations occurred. The results indicate that SA-NPs could better address the issue of wellbore instability in shale formations and have a great application prospect in shale well drilling.

Lubricity and Rheological Properties of Highly Dispersed Graphite in Clay-Water-Based Drilling Fluids

Improving the tribological characteristics of water-based drilling fluids by adding graphene-based lubricants has garnered attention because of the potential for a range of inorganic-material-based additives at high temperature. In this study, we constructed a green and simple adsorption approach to prepare highly dispersed graphite using a cationic surfactant for graphite modification. The findings demonstrated that the prepared graphite was highly dispersed in water and had a low sedimentation rate and small contact angle in distilled water. The concentration dosage of cetyltrimethylammonium chloride (CTAC) on graphite was 0.02 g/g. We evaluated the performance of the modified graphite as a lubricated additive in water-based drilling through a rheological study and viscosity coefficient measurement. The results showed that the viscosity coefficient of drilling fluid with 0.05% modified graphite was reduced by 67% at 180 °C. We proved that the modified graphite can significantly improve the lubrication performance of drilling fluid. Furthermore, we revealed the lubrication mechanism by analyzing the chemical structural and crystalline and morphological features of graphite through a particle size test, zeta potential test, Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) measurements. The results indicated that the modification of graphite by CTAC only occurs through physical adsorption, without changing the crystal structure. These findings provide a reference for the development of high-performance water-based drilling fluids.

Star Polymer for Filtration Control in Water-based Fluids

In high-performance water-based drilling fluids, filtration control is a closely monitored mud characteristic. Several problems have been found that are linked to excessive invasion of aqueous filtrate into a permeable formation. A high filtrate loss often causes thick filter cake formation that lead to tight spots in the hole. Elevated temperatures and fluid loss in deep holes can cause situations such as differential sticking of pipes. At the same time, loss of filtration control catastrophically affects the rheology of the water-based fluid via excessive thickening. Seepage of the filtrate into sensitive shale formations may lead to swelling, sloughing or even cave-in. Filtrate invasion into a production zone can lead to a condition known as water blocking, where the reservoir pressure is not strong enough to drive the aqueous filtrate out of the pores, leading to drastic reduction of oil and gas flow. In this contribution, we explore the synthesis of a novel star block copolymer fluid loss control additive using reversible addition-fragmentation chain transfer (RAFT) polymerization using arm-first approach. The star polymer developed in this work is able to provide superior filtration control performance (3 to 6 times better performance) over commercial additives. In addition, the thermal and mechanical stability of this novel material afforded direct incorporation into drilling mud formulations commonly used in the middle east drilling operations, which led to excellent fluid loss control both at room temperature and high temperature, high pressure conditions with thin filter cakes.

Analysis of Development Status of High Performance Water-based Drilling Fluid

Deep wells, ultra deep wells and unconventional oil and gas exploitation have gradually become the focus of exploration and development. The oil-based drilling fluid is gradually replaced by water-based drilling fluid because of the impact of cost and environmental protection factors. In order to better replace oil-based drilling fluid, research on high-performance water-based drilling fluid has been carried out at home and abroad, and its comprehensive performance has gradually approached that of oil-based drilling fluid. The research progress and future development trend of high performance water-based drilling fluid abroad are introduced.

Application of sustainable basil seed as an eco-friendly multifunctional additive for water-based 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.

Novel modified nano-silica/polymer composite in water-based drilling fluids to plug shale pores

ABSTRACT The rapid growth of global energy demand necessitates high-performance water-based drilling fluids (WDFs) with excellent-plugging performance in the deep excavation of shale gas formation. Herein, we report an organic-inorganic nanocomposite (NS-D) as a plugging agent in WDFs to plug the nanoporous of shale and abate the hydration expansion of shale by integrating the advantages of inorganic and polymer nano plugging agents. The results of Fourier Transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (H-NMR) revealed that NS-D had been successfully obtained. Additionally, thermogravimetric analysis (TGA) showed that the thermal degradation temperature of NS-D occurred after 354 °C. The results of plugging theory analysis showed that the presence of rich amide groups and rigid material silica not only made NS-D adhere to shale efficiently by hydrogen bonding, but also firmly blocked the nanoporous of shale. The plugging ability was evaluated by pressure transfer test and nitrogen adsorption test. The results showed that WDFs with NS-D can significantly improve plugging efficiency and reduce fluid invasion. On the other hand, NS-D sharply abated the fluid loss of WDFs due to its positive plugging performance. The filtrate volume of WDFs decreased by 90.5% and 88.3%, respectively, before and after hot rolling at 150°C for 16 h. Moreover, the plugging performance of NS-D for WDFs was significantly better than polymer plugging agent crosslinked polyacrylamide microspheres and inorganic plugging agent silica nanoparticles. This work provides a novel strategy to plug the nanoporous of shale in the process of shale gas exploration.

Development of high-performance water-based drilling fluid using biodegradable eco-friendly additive (Peanut Shells)

Development of high-performance water-based drilling fluid using biodegradable eco-friendly additive (Peanut Shells)

Environmentally friendly and salt-responsive polymer brush based on lignin nanoparticle as fluid-loss additive in water-based drilling fluids

The sustainable development of global energy necessitates high-performance water-based drilling fluid (WDFs) with low toxicity and sustainability, especially in high salinity reservoir excavation. Herein, we report an environmentally friendly and salt-responsive zwitterionic polymer brush based on enzymatic lignin nanoparticles (EHL) prepared by intramolecular self-assembly as a fluid-loss additive (EHL-ASN) for WDFs by the anti-polyelectrolyte effect to overcome the issues of wellbore instability and collapse caused by the deterioration of rheological and filtration properties of WDFs due to electrolyte invasion in drilling high salinity reservoirs and reveal the salt response mechanism of EHL-ASN. The ascending viscosity of EHL-ASN solution corresponded to the heightening of electrolyte salinity, which revealed that EHL-ASN solution had obvious salt response. The biological toxicity evaluation of EHL-ASN exhibited that its half maximal effective concentration (EC50) was 51,900 mg/L, which accorded with the direct emission standard. Additionally, the results for rheological and fluid-loss performance evaluation of EHL-ASN/WDFs promulgated that EHL-ASN had significant effects on heightening viscosity and debasing fluid-loss, in which, EHL-ASN could significantly debase the fluid-loss (FLAPI) of saturated salt-based mud (SSBM) from 194 mL to 4 mL, with a decline rate of 97.9%. This work not only provides a novel approach for high value utilization of lignin, but also paves the way for the development of environmentally friendly intelligent WDFs.

Application of high-performance water-based drilling fluid system in Mahu oilfield

The Baikouquan Formation in Block 18 of Mahu Oilfield, Xinjiang, is easily hydrated with mud shale; it exhibits poor cementation speed, low mechanical drilling speed, and high accident and complexity rates during drilling. The existing water-based drilling fluids show poor inhibitory properties, insufficient lubrication and anti-seize, and insufficient plugging ability for pores and micro-fractures, so it cannot easily satisfy construction requirements. In the present study, a strong inhibitor YZFS-1 and a wall-fixing agent GBFS-1 are introduced based on the existing water-based drilling fluid system to build a set of high-performance water-based drilling fluid system that has successful applications in a well. As revealed from the results of its field application: XZ high-efficiency water-based drilling fluid system exhibits stable rheology, low filtration loss, robust suppression ability and regular well diameter, and without the presence of downhole complex accidents. As compared with adjacent wells, the system of this study exhibits high drilling speed, a short cycle, low cost and significant effects, providing a solid technical guarantee for safe and efficient development in the area.

Evaluation of polymer/bentonite synergy on the properties of aqueous drilling fluids for high-temperature and high-pressure oil wells

The increasing demand for energy sources has led to oil field exploration under inhospitable conditions, where non-aqueous drilling fluids are commonly used due their physical and chemical stability. However, they exhibit a number of environmental constraints and the cuttings produced require expensive treatments before disposal. Aqueous drilling fluids are currently less thermally resistant and generally entail the use of chromium lignosulfonate as clay dispersant, which provides stability to rheological properties and filtration control under high temperature and high pressure (HTHP). This study elucidates the role played by synergic effect of a novel eco-friendly high-performance water-based drilling fluid using bentonite and vinyl polymers (polyvinylpyrrolidone (PVP) and partially hydrolyzed polyacrylamide (PHPA)) as the main constituents. Filtration and rheological properties of the drilling fluids were determined on a HTHP filtration system and on a rotational viscometer, respectively. Systems using high molar mass PVP (HMM PVP) showed higher values for viscosity, gel strength and yield stress, due to promotion of flocculation. On the other hand, dispersed systems were obtained using low molar mass PVP (LMM PVP), through ion-dipole interactions between PVP and clay particles. Dispersed systems provided stable rheological parameters over the entire range of temperature and pressure studied (up to around 120 °C and 3450 kPa). Linear clay swelling tests showed that LMM PVP and water had similar profiles, promoting clay dispersion. Profitable low filtrate volumes (12 mL) were obtained for PVP-based drilling fluids in conditions where non-aqueous fluids are currently applied.

Technical Progress on Environmental-Friendly, High-Performance Water-Based Drilling Fluids

Technical Progress on Environmental-Friendly, High-Performance Water-Based Drilling Fluids

Laponite: a promising nanomaterial to formulate high-performance water-based drilling fluids

High-performance water-based drilling fluids (HPWBFs) are essential to wellbore stability in shale gas exploration and development. Laponite is a synthetic hectorite clay composed of disk-shaped nanoparticles. This paper analyzed the application potential of laponite in HPWBFs by evaluating its shale inhibition, plugging and lubrication performances. Shale inhibition performance was studied by linear swelling test and shale recovery test. Plugging performance was analyzed by nitrogen adsorption experiment and scanning electron microscope (SEM) observation. Extreme pressure lubricity test was used to evaluate the lubrication property. Experimental results show that laponite has good shale inhibition property, which is better than commonly used shale inhibitors, such as polyamine and KCl. Laponite can effectively plug shale pores. It considerably decreases the surface area and pore volume of shale, and SEM results show that it can reduce the porosity of shale and form a seamless nanofilm. Laponite is beneficial to increase lubricating property of drilling fluid by enhancing the drill pipes/wellbore interface smoothness and isolating the direct contact between wellbore and drill string. Besides, laponite can reduce the fluid loss volume. According to mechanism analysis, the good performance of laponite nanoparticles is mainly attributed to the disk-like nanostructure and the charged surfaces.

Experimental study on water-based drilling fluid for horizontal wells

ABSTRACT High-yield shale gas flow has been discovered in the Cambrian Shuijingtuo group shale (the Shuijingtuo shale) of the first shale gas well of Yichang, West Hubei, China. However, there are very few papers or reports involving high-performance water-based drilling fluid for the Shuijingtuo shale. X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) tests were conducted on the outcrop of the Shuijingtuo shale samples collected from Zigui County, West Hubei. Then, the screening experiments on mud-making materials, salt additives, nanoparticles, fluid loss additives, mixed metal hydroxides (MMH), and surfactants were carried out. A high-performance water-based drilling fluid for the Shuijingtuo shale (the SWDF drilling fluid) was proposed based on physical plugging by nanoparticles, electrical property inhibition, and wettability control theory. Finally, comprehensive appraisals on rheology, filtration, lubricity, temperature resistance, inhibition, anti-pollution capability, and expense of the SWDF drilling fluid were accomplished. XRD results showed that the Shuijingtuo shale samples had 55%~67% brittle minerals. Clay minerals were mainly illite (13%~27%), and no montmorillonite was observed, which indicated that the Shuijingtuo shale was a weak-expansive rock. SEM analysis results show that pore and micro-cracks on the surface of the Shuijingtuo shale could provide natural channels for the invasion of drilling fluid. Nanomaterials were found to reduce the fluid loss of drilling fluid and thermal stability of the nano-silica dispersion was better. As a whole, the SWDF drilling fluid had suitable viscosity and gel strength, a low API fluid loss of 7.2 mL, a lubricity coefficient of 0.21, temperature-resistance capability up to 120°C, and good inhibition to shale hydration. In addition, it had excellent resistance capability to inorganic salts (NaCl, MgCl2, and CaCl2) and low-yield mud-making materials (simulated cuttings). Also, the cost of the SWDF drilling fluid was competitive compared to common oil-based drilling fluids. As a consequence, the SWDF drilling fluid can meet the requirements of drilling horizontal wells in the Shuijingtuo shale of West Hubei, China.

Super-amphiphobic, strong self-cleaning and high-efficiency water-based drilling fluids

Abstract Based on the amphiphobic theory on underground rock surface, a super-amphiphobic agent is developed and evaluated which can form nano-micro papilla structure on rock, filter cake and metal surface, reduce surface free energy, prevent collapse, protect reservoir, lubricate and increase drilling speed. With this super-amphiphobic agent as the core agent, a super-amphiphobic, strong self-cleaning and high-performance water-based drilling fluid system has been developed by combining with other agents based on drilled formation, and compared with high-performance water-based drilling fluid and typical oil based drilling fluid commonly used in oilfields. The results show that the super-amphiphobic, strong self-cleaning and high-performance water-based drilling fluid has better rheology, and high temperature and high pressure filtration similar with that of oil-based drilling fluid, inhibiting and lubricating properties close to oil based drilling fluid. Besides, the super-amphiphobic system is non-toxic, safe and environmentally friendly. Field tests show this newly developed drilling fluid system can prevent wellbore collapse, reservoir damage and pipe-sticking, increase drilling speed and lower drilling cost, meeting the requirement of safe, high efficient, economic and environmentally friendly drilling. Compared with other drilling fluids, this new drilling fluid system can reduce downhole complexities by 82.9%, enhance the drilling speed by about 18.5%, lower drilling fluid cost by 39.3%, and increase the daily oil output by more than 1.5 times in the same block.