Oil-based Fluids Research Articles

Comparative study on the use of cationic–nonionic-organo-montmorillonite in oil-based drilling fluids

This work involves a comparative study of cationic–nonionic-organo-montmorillonite (CNOMt), cationic-organo-montmorillonite (COMt) and nonionic-organo-montmorillonite (NOMt), aiming their use in oil-based drilling fluids. Firstly, CNOMt, COMt and NOMt were prepared in aqueous solution. Secondly, organo-montmorillonites were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TG), contact angle test, and swell index. The results indicated that cationic and nonionic surfactants could solely or synergistically intercalate into the interlayer spaces of montmorillonite. The order of their thermal stabilities was CNOMt>NOMt>COMt. The order of surface lipophilicity (or hydrophobicity) and swelling indices in oils was the same, i.e., CNOMt>COMt>NOMt. Finally, organo-montmorillonites were added into emulsions with different ratios of oil to water and their apparent viscosities were characterized. The results exhibited that both CNOMt and COMt viscosified the oil-based fluids better than NOMt did. In addition, the apparent viscosity of CNOMt was a little higher than that of COMt in the emulsion with oil/water ratio of 95:5 while the result was inverted in the emulsion with oil/water ratio of 80:20. From the standpoint of characterization results, CNOMt presented a new kind of potential rheological control additive of oil-based drilling fluids, especially for high oil/water ratio fluids, and CNOMt would perform excellent thermal stability.

Hypothetical exposure limits for oil-based metalworking fluids and cardiovascular mortality in a cohort of autoworkers: structural accelerated failure time models in a public health framework.

Occupational exposure to aerosolized particles of oil-based metalworking fluid was recently linked to deaths from ischemic heart disease. The current recommended exposure limits might be insufficient. Studying cardiovascular mortality is challenging because symptoms can induce sicker workers to reduce their exposure, causing healthy-worker survivor bias. G-estimation of accelerated failure time models reduces this bias and permits comparison of multiple exposure interventions. Michigan autoworkers from the United AutoWorkers–General Motors cohort (n = 38,666) were followed from 1941 through 1994. Separate binary variables indicated whether annual exposure exceeded a series of potential limits. Separate g-estimation analyses for each limit yielded the total number of life-years that could have been saved among persons who died from specific cardiovascular causes by enforcing that exposure limit. Banning oil-based fluids would have saved an estimated 4,003 (95% confidence interval: 2,200, 5,807) life-years among those who died of ischemic heart disease. Estimates for cardiovascular disease overall, acute myocardial infarction, and cerebrovascular disease were 3,500 (95% confidence interval: 1,350, 5,651), 2,932 (95% confidence interval: 1,587, 4,277), and 917 (95% confidence interval: −80, 1,913) life-years, respectively. A limit of 0.01 mg/m3 would have had a similar impact on cerebrovascular disease but one only half as great on ischemic heart disease. Analyses suggest that limiting exposure to metalworking fluids could have saved many life-years lost to cardiovascular diseases in this cohort.

Experimental study on crack propagation in shale formations considering hydration and wettability

Cracks in shale formations exhibit an important influence over wellbore stability of shale gas wells, and the interaction between the drilling fluid and shale affect the crack propagation mechanism in shale formation. In this paper, the outcrop shale samples from the Lower Silurian Longmaxi Formation (LF) in the Sichuan Basin of China are carried out laboratory experiments to investigate the wettability and hydration by spontaneous imbibition. Based on the fracture mechanics, a crack propagation model was established for the shale formation with the hydration stress and capillary force, and the influences of hydration by spontaneous imbibition and capillary effect on the crack propagation mechanism in shale formation were discussed. The results indicate the LF shale wettability is both water-wet and oil-wet and tends to be more oil-wet. The hydration stress of the shale tends to ascend first before stabilizing with increasing immersion time. The surface fractures of the shale samples exhibit parallel bedding plane immersion in water. Increasing the immersion time causes the shale samples to spall into pieces. The capillary effect influences the stress intensity factor with a critical width of 0.6 mm. The hydration and capillary effect positively influence the stress intensity factor, and drilling fluid systems should decrease their drilling fluid filter loss, increase their clay minerals hydrate inhibitor, reduce their drilling fluid interfacial tension and enlarge the contact angle between the drilling fluid and rock medium. The water-base fluids have a significant positive influence on crack propagation in shale formation, whereas the oil-base fluids have a less positive impact on crack propagation in shale formations. Therefore, the oil-based drilling fluids better maintain wellbore stability during when drilling in shale formations.

Pushing the Frontier through Wellbore Strengthening

Drilling Fluid Technology Making hole has become a more difficult and complex operation as operators move into untapped horizons, especially deepwater and unconventional fields. It is this increased difficulty that is driving a growing number of companies to invest millions of dollars in advanced materials that seek to make drilling wells easier. The technologies many are working on involve not mechanical systems, but advanced chemistry and physical science. Some are using nanoparticles and others are reworking older technologies by adding new substances, all in an effort to make the undrillable drillable. Those reaching for this prize include teams of university researchers, young technology startups, and established firms that are buying intellectual property from others so they can join the race. Different groups are designing drilling-fluid additives and other materials that they claim make unstable wellbore walls stronger by preventing and sealing fractures as the drill bit eats its way down to the pay zone. The importance of these wellbore-strengthening objectives is well understood by drillers who have suffered sudden losses of drilling fluids into the rock formation through fractures, which can lead to gas kicks and catastrophic blowouts, or those who have had to deal with stuck pipe because of a collapsed borehole. For petroleum engineers, preventing these problems with new technology means they can design simpler, cheaper, and safer wells with fewer casing strings. For the boardroom, wellbore strengthening means executives can promise better returns and higher flow rates to investors because large-diameter casing strings can be placed into the production zone. And for the industry in general, wellbore strengthening means wells that many consider too dangerous or too hard to drill may soon become tamed. Clay-Stabilizing Nanoparticles for Water-Based Drilling Fluids In April, downhole chemical technology provider Flotek Industries acquired water-based, drilling fluid-additive technology from ARC Drilling Fluids. Flotek hopes to use the technology, which it markets as Microsolutions, in areas where using oil-based drilling fluids have traditionally been the only option. Drilling fluids that use water as a base are far cheaper than oil-based fluids, making them more desirable, but oil is less reactive with many rock formations. Wellbore Strengthening: The Mechanical Option Before many of the new chemical and nanoparticle technologies for wellbore strengthening arrived to the marketplace, casing while drilling (CWD) was used for more than a decade to mechanically achieve the same end. Weatherford International and other service companies have developed multiple technologies for CWD, as well as the similar method of liner drilling (LD). With CWD, the casing is the drillstring, and with LD, the liner is the drillstring.

Wellbore instability in shale gas wells drilled by oil-based fluids

Wellbore instability in shale gas wells drilled by oil-based fluids

Organofilization of Smectite Clay from Pedra Lavrada, PB, with Nonionic Surfactant

The petroleum industry has been investing for many years in the use of smectite as dispersant agent in the composition of oil-based and water-based fluids for drilling oil wells. The State of Paraíba is one of the largest producers of such clays and new deposits have been recently discovered in the regions of Cubati and Pedra Lavrada, causing many expectations for the expansion of the national mineral production. The objective of the present work is the organofilization of smectite clay from Pedra Lavrada, PB, through the addition of nonionic surfactant. After organofilization, the clay was characterized through X-ray diffraction and Foster swelling, so that the most suitable surfactant could be chosen for diesel as organic dispersant media. The results show that the incorporation of the surfactant used with the clay caused a significant increase in the interlamellar distance, and that the dispersions presented rheological properties that meet Petrobras' specifications for the use of organoclays in non aqueous based drilling fluids. Keywords: Smectite, drilling fluids, organofilization.

Effect of Different pH on Characterization of Oil-Based Magnetic Fluid

In this paper, the oil-based magnetic fluid was prepared by chemical co-precipitation method and sodium oleate was the surfactant. The effect of different pH on the characterization of magnetic fluid was studied. The characterization was detected by Fourier Transform Infrared spectroscopy (FT-IR), Transmission Electron Microscope (TEM) and Vibrating Sample Magnetometer (VSM). The results show that the nanoparticles were coated successfully by sodium oleate at pH=5. And the saturation magnetization of Fe3O4 magnetic nanoparticles is 58.0 emu/g, the saturation magnetization of magnetic fluid prepared is 20.2 emu/g, and the Fe3O4 particles are dispersed well. Although the Fe3O4 magnetic particles coated by sodium oleate at pH = 10.5 has a higher saturation magnetization (67.8 emu/g), but the magnetic fluid is less stable and has an obvious settlement phenomenon.

Combined Effect of Pressure and Temperature on the Viscous Behaviour of All-Oil Drilling Fluids

The overall objective of this research was to study the combined influence of pressure and temperature on the complex viscous behaviour of two oil-based drilling fluids. The oil-based fluids were formulated by dispersing selected organobentonites in mineral oil, using a high-shear mixer, at room temperature. Drilling fluid viscous flow characterization was performed with a controlled-stress rheometer, using both conventional coaxial cylinder and non-conventional geometries for High Pressure/High Temperature (HPHT) measurements. The rheological data obtained confirm that a helical ribbon geometry is a very useful tool to characterise the complex viscous flow behaviour of these fluids under extreme conditions.The different viscous flow behaviours encountered for both all-oil drilling fluids, as a function of temperature, are related to changes in polymer-oil pair solvency and oil viscosity. Hence, the resulting structures have been principally attributed to changes in the effective volume fraction of disperse phase due to thermally induced processes. Bingham’s and Herschel-Bulkley’s models describe the rheological properties of these drilling fluids, at different pressures and temperatures, fairly well. It was found that Herschel-Bulkley’s model fits much better B34-based oil drilling fluid viscous flow behaviour under HPHT conditions.Yield stress values increase linearly with pressure in the range of temperature studied. The pressure influence on yielding behaviour has been associated with the compression effect of different resulting organoclay microstructures. A factorial WLF-Barus model fitted the combined effect of temperature and pressure on the plastic viscosity of both drilling fluids fairly well, being this effect mainly influenced by the piezo-viscous properties of the continuous phase.

Influence of viscosity modifier nature and concentration on the viscous flow behaviour of oil-based drilling fluids at high pressure

This work deals with the effect of viscosity modifier nature and concentration on the rheological properties of model oil-based drilling fluids (OBM) submitted to high pressure. The oil-based fluids were formulated by dispersing, with a high shear mixer, two selected organobentonites in a mineral oil, at room temperature. The viscous flow behaviour of the corresponding dispersions was characterised as a function of pressure, organoclay nature and organoclay concentration, using a controlled-stress rheometer equipped with both pressure cell and coaxial cylinder geometries. A factorial Sisko–Barus model, which takes into account both shear and pressure effects in the same equation, fitted the experimental pressure–viscosity data fairly well.The influence of disperse phase concentration on the shear-thinning characteristics of these organoclay dispersions is related to the development of different microstructures, which depend on organoclay nature. In this sense, the resulting microstructure has been attributed to the cohesion energy between microgels domains. From the experimental results obtained, it can be concluded that the viscous flow behaviour of the OBM investigated is strongly affected by organoclay nature and concentration. The pressure–viscosity behaviour of these dispersions is mainly influenced by the piezoviscous properties of the oil and the properties of the continuous phase. The Sisko–Barus model proposed can be a useful tool, from an engineering point of view, for calculating pressure losses in the different sections of the bore, as well as being of significant help to solve other additional problems, such as hole cleaning, induced fracturing, and hole erosion during the drilling operation.

Waterless fracturing fluid with low carbon hydrocarbon as base fluid for unconventional reservoirs

Abstract As the conventional fracturing fluids are not good for stimulation of unconventional reservoirs and the conventional oil-based fracturing fluids crosslink slowly, a ferric-complex cross-linking agent that cross-links fast with dialkyl phosphate ester was prepared and the fracturing fluid systems for the unconventional reservoirs were obtained. The main influencing factors on the properties of the cross-linking agent were analyzed and optimized, and then the ferric-complex cross-linking agent was prepared based on the optimizing results and its performance was evaluated. The optimizing and evaluating results show that: The ferric-complex cross-linking agent with excellent performance can be obtained in the condition that the content of cross-linking promoting agent is 5%, the content of ethylene glycol is between 8% and 10%, and the complexing agent is L5 with content of 10%. The ferric-complex cross-linking agent has better performance than ferric sulfate and aluminium sulfate. It is found that the crosslinking slows down with the growth of carbon chain when using different base fluids. The fracturing fluid systems with low carbon hydrocarbon (such as LPG) as base fluid, dialkyl phosphate ester as gelling agent and ferric complex as cross-linking agent are developed, and all of them have excellent crosslinking performance and are suitable for unconventional reservoirs.

Evaluation of tractor biodegradable hydraulic fluids on the basis of hydraulic pump wear

Two types of biodegradable hydraulic fluids (HEES and HEPR) with the mineral oil-based hydraulic fluid (HV) were compared. The tests were performed using a test bench. During the tests with a tractor hydraulic pump, the fluids were loaded by a cyclic pressure load. The tests of fluids were evaluated on the basis of wear of the pump. Evaluation parameters were the flow characteristics of the pump and the cleanliness level of tested fluids. The temperature of the fluid under which the test was performed was measured in real operating conditions of the Zetor Forterra 11441 tractor. It is possible to state upon the test results that the mineral oil-based fluid was classified in the first place, the biodegradable fluid of the HEPR type in the second place, and the biodegradable fluid of the HEES type received the last position.  

Gold/Oil Nanofluids Stabilized by a Gemini Surfactant and Their Catalytic Property

With surfactants, butanediyl-1,4-bis(dimethylcetyl ammonium bromide) (16–4–16), and N,N-dimethylhexadecylamine (C16DMA), as the stabilizers and surface-modified reagents, stable oil-based nanofluids containing hydrophobic gold nanoparticles have been prepared. The gemini surfactant 16–4–16 shows better performance than C16DMA for controlling the growth of gold particles. The gold nanoparticles modified by 16–4–16 are dispersed well in oil-based fluids. The nanofluids can be treated as pseudohomogeneous catalyst systems. The viscosities at different temperatures of the nanofluids containing the surface-modified gold nanoparticles with the gemini surfactant 16–4–16 are measured. Catalytic cracking of tricycle [5.2.1.02.6] decane (JP-10) with surface-modified gold nanoparticles as the catalyst has been investigated. The catalytic cracking exhibits clearly enhanced conversion in comparison with the thermal cracking.

Utilization of Drilling Fluid Base Oil Hydrocarbons by Microorganisms Isolated from Diesel-Polluted Soil

Hydrocarbon-degrading microorganisms identified as Pseudomonas luteola, Pseudomonas alcaligenes, Pseudomonas aeruginosa, and Actinomyces sp. were isolated from diesel oil-polluted soils using an enrichment culture technique. The isolates grew luxuriantly on hydrocarbons, including crude oil, diesel, kerosene, engine oil, cyclohexane, and dodecanol. Naphthalene and pyrene were poorly utilized, while there was no growth on benzene. The organisms utilized drilling fluid base oil as the sole source of carbon and energy, with rapid exponential growth at a rate ranging from 0.015 to 0.094 h−1. The concomitant doubling time was between 7.4 and 45.5 h. Gas chromatographic analyses of the culture revealed reduction in the height of the n-alkane peaks, confirming biodegradation of the compounds. Among the isolates, P. alcaligenes had the highest (99.4%) percentage hydrocarbon degradation. Remarkable (99.2% and 98.7%) hydrocarbon removal was also noted for P. luteola and P. aeruginosa, while the lowest (92.3%) value was recorded in Actinomyces sp. These bacteria with high degradative capacity for hydrocarbons in oil-based drilling fluids would be useful in bioremediation of a tropical environment, polluted with spent drilling mud and drill cuttings.

Cuttings Transport with Foam in Highly Inclined Wells at Simulated Downhole Conditions / Transport urobku wiertniczego przy użyciu piany w silnie nachylonych otworach w symulowanych warunkach w otworze

Along with the rapidly growing demand and development activities in unconventional resources, is the growth of environmental awareness and concerns among the public. Foam, as an alternative to traditional drilling fluid, is gaining more and more momentum in the drilling industry. Drilling with foam can minimize formation damage, water usage, and drag and torque. Foam also costs less and leaves a much smaller environmental footprint than other commonly used drilling fluids, such as synthetic oil-based fluids, when developing vulnerable formations such as shale gas. As drilling in horizontal and near horizontal sections has become very common, and the need for such sections is increasing, it is very important to understand cuttings transport and hole cleaning issues when drilling with foam in such sections. A team from University of Tulsa Drilling Research Projects (TUDRP) conducted a series of experiments focused on studying the effects of change in hole inclination angle from 90 degrees to 70 degrees on cuttings transport with foam under Elevated Pressure and Elevated Temperature (EPET) conditions. This experimental and theoretical study also includes other influential parameters such as foam quality, foam flow rate, polymer concentration and drill pipe rotary speed. We have observed that there is no significant difference in cuttings concentration and frictional pressure losses as inclination changes from 70 to 90 degrees. Also, an increase in superficial foam velocity reduces cuttings concentration within the annulus. Pipe rotation influences cuttings concentration and frictional pressure losses for low quality foams, but does not have a significant effect on high quality foams. A correlation for the cuttings bed area and a computer simulator are developed for practical design and field applications. The predicted results are compared with experimental results from this study and previous studies. The comparison shows good agreement. We believe that the findings of this paper will help designers with the choice of optimal drilling fluid for drilling horizontal wells in unconventional (shale) gas/oil reservoirs.

The Influence of Base Oil and Thixotropy on Magnetorheological Property of MRF

Adopting carbonyl iron powder and silicone/mineral oil as suspend phase and dispersed phase separately,and silica, kaolin as lubricant additives,magnetorheological (MR) fluid was prepared by ball milling. The apparent viscosity of base oil and shear stress were measured on a modified rotational viscometer. The experimental results demonstrated that an appropriate viscosity of base oil contributed to the rheology of MRF. Adding a small amount of thixotropy into MRF had little influence on zero-field viscosity, which facilitated the application of MRF to maintain adequate liquidity. Under low shear rate conditions, the shear stress was improved by adding thixotropy to some extent, especially in the mineral oil-based magnetorheological fluid, in which the role of silica was superior to kaolin.

Full Factorial Design to Study Material Parameters of Magnetorheological Fluid

This paper presents the effects of magnetorheological (MR) fluid parameters, bidisperse ratio, carrier fluid viscosity and particle volume fraction, on its mechanical behaviour using statistical investigation. Silicone oil-based MR fluid samples were compressed using universal testing machine (UTM) in a vertical direction. A set of eight experiments was designed by Design Expert 7 software in which was conducted at two levels for each factor. Stress-strain curves that obtained from the compression test were then analysed by testXpert analyser software. The responses in terms of maximum stresses at 0.75 of strain were extracted from the curves. The result indicated that a combination of high bidisperse ratio and particle volume fraction, and a low carrier fluid viscosity could produce a high compressive stress. The findings are important to be considered in designing squeeze mode MR fluid actuators.

Study on the Preparation and Properties of Silicone Oil-Based Magnetorheological Fluids

Aiming to improve the performance of magnetorheological fluids (MRF) applied in mechanical transmission system, a preparation method of silicone oil-based magnetorheological fluids is proposed, and the properties of prepared MRF are tested. The materials for MRF preparation are elaborated, and the process parameters and flowchart are designed. Moreover, scanning electron microscope is used to observe the changes between uncoated magnetic-particles and coated magnetic-particles, and three samples with the volume fractions of magnetic-particles 10%, 20%, and 30% are prepared. Finally, three properties of prepared MRF are tested. Analysis of the experimental results shows that the prepared MRF can satisfy the requirement of mechanical transmission system, and the optimal process parameters are illustrated.

Technology Focus: Well Integrity (January 2013)

Technology Focus I am honored to be the first JPT Editorial Committee member to write the introduction of January’s Technology Focus section under a new title: Well Integrity. With this alteration, this section broadens its scope, not only focusing on topics related to well control but also now covering all safety aspects concerning the construction, maintenance, and abandonment of wells. The importance of well integrity has been recognized by the oil industry for a long time, and great effort has been made to improve the design and operational procedures during the well design and construction processes and throughout the entire well life cycle. Despite these efforts, many well integrity related problems still occur. This indicates that investing in well integrity is a strategic approach to minimize design and operational risks that may jeopardize personnel safety, the environment, and the operator’s image, reputation, and assets. Last November, I had the opportunity to be the chairperson of an Applied Technology Workshop (ATW) in Salvador, Brazil. This ATW was the third of the Global Integrated Workshop Series on Well Integrity and focused on deepwater issues. The quality and appropriateness of the presentations were remarkable, as were the discussions following the presentations. In the area of well construction, the challenges of drilling in near-salt rubble zones were presented in relation to well integrity (lost circulation and wellbore instability) and the use of high-performance water-based drilling fluids as an alternative to synthetic oil-based fluids considering the borehole instability. It is important to note that borehole instability issues are also considered part of the well integrity domain. Concerning producing wells, the most important aspects discussed were the importance of managing annulus pressure during production, the use of solid expandable liners in recompletions in mature fields, and solutions for casing leaks. The importance of safety barrier assurance was stressed. Zonal isolation by cementing was an important point when considering the integrity of the well during and after its abandonment. Revisions or elaborations of new standards were presented with emphasis on American Petroleum Institute RP 96, NORSOK D-010, and a new International Organization for Standardization standard on well integrity production operations. The most important aspects regarding deepwater well integrity were reliability of subsea blowout preventers, evaluation of the probability of uncontrolled leakage in subsea producing wells, a nonintrusive device for monitoring B-annulus pressure in subsea wells, and cementing of shallow hazard zones. Recommended additional reading at OnePetro: www.onepetro.org. SPE/IADC 151381 Dynamic Modeling of Gas Distribution in the Wellbore During Kick Situations by H.F. Spoerker, OMV Exploration/Production, et al. SPE 146231 Casing- and Screen-Failure Analysis in Highly Compacting Sandstone Fields by Kenji Furui, ConocoPhillips, et al. SPE/IADC 151181 Use of Liner Drilling Technology as a Mitigation to Loss Intervals and Hole Instability: A Case Study in Mississippi Canyon by Steven M. Rosenberg, Weatherford, et al.

Discharged drilling waste from oil and gas platforms and its effects on benthic communities

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 456:285-302 (2012) - DOI: https://doi.org/10.3354/meps09622 REVIEW Discharged drilling waste from oil and gas platforms and its effects on benthic communities J. I. Ellis1,*, G. Fraser2, J. Russell3 1Coastal & Freshwater Research Group, Cawthron Institute, Private Bag 2, Nelson 7010, New Zealand 2Faculty of Environmental Studies, York University, Toronto, Ontario M6H 1T5, Canada 3Alder Institute, Tors Cove, Newfoundland A0A 4A0, Canada *Email: joanne.ellis@cawthron.org.nz ABSTRACT: This review paper identifies the main effects of oil and gas drilling waste on benthic environments. We identified 26 papers and technical reports that surveyed sediment samples from 72 production or exploration platform sites to assess the zone of influence of sediment contamination and biological effects on benthic communities. While oil-based fluids are now rarely used in the marine context, their release has had large-scale (out to 6 km) and persistent (decadal time scale) impacts on benthic communities. The zone of influence of water-based drilling fluids as determined by sediment barium concentration was larger (2 to 20 km) than for synthetic-based fluids (200 to 2000 m). The zone of biological effects on benthic community diversity and abundance ranged from 100 to 1000 m for both water and synthetic fluids. Effects include changes in benthic species diversity, abundance and alterations to community structure. Functional changes included a loss of suspension-feeding species and increases in deposit feeders and polychaetes. In general, this review demonstrates a loss of benthic biodiversity and suspension-feeding communities due to oil exploration and production and the potential for large-scale effects on sensitive communities such as deep-sea, coral and vegetated habitats. Current research gaps and priorities are identified. KEY WORDS: Benthic community composition · Chemical toxicity · Organic enrichment · Suspended sediments · Oil-based fluids · Synthetic-based fluids · Water-based fluids Full text in pdf format PreviousCite this article as: Ellis JI, Fraser G, Russell J (2012) Discharged drilling waste from oil and gas platforms and its effects on benthic communities. Mar Ecol Prog Ser 456:285-302. https://doi.org/10.3354/meps09622 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 456. Online publication date: June 07, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Using relative permeability curves to evaluate phase trapping damage caused by water- and oil-based drilling fluids in tight-gas reservoirs

Low matrix permeability and significant damage mechanisms are the main signatures of tight-gas reservoirs. During the drilling and fracturing of tight formations, the wellbore liquid invades the tight formation, increases liquid saturation around the wellbore, and eventually reduces permeability at the near wellbore zone. The liquid invasion damage is mainly controlled by capillary pressure and relative permeability curves. Due to high critical water saturation, relative permeability effects and strong capillary pressure, tight formations are sensitive to water invasion damage, making water blocking and phase trapping damage two of the main concerns with using a water-based drilling fluid in tight-gas reservoirs.Therefore, the use of an oil-based mud may be preferred in the drilling or fracturing of a tight formation. Invasion of an oil filtrate into tight formations, however, may result in the introduction of an immiscible liquid-hydrocarbon drilling or completion fluid around the wellbore, causing the entrapment of an additional third phase in the porous media that would exacerbate formation damage effects. This study focuses on phase trapping damage caused by liquid invasion using a water-based drilling fluid in comparison with the use of an oil-based drilling fluid in water-sensitive, tight-gas sand reservoirs. Reservoir simulation approach is used to study the effect of relative permeability curves on phase trap damage, and the results of laboratory experiments of core flooding tests in a West Australian tight-gas reservoir are shown, where the effect of water injection and oil injection on the damage of core permeability are studied. The results highlight the benefits of using oil-based fluids in drilling and fracturing of tight-gas reservoirs in terms of reducing skin factor and improving well productivity.