Wettability Alteration of Sandstone by Chemical Treatments

Liquid condensation in the reservoir near a wellbore may kill gas production in gas-condensate reservoirs when pressure drops lower than the dew point. It is clear from investigations reported in the literature that gas production could be improved by altering the rock wettability from liquid-wetness to gas-wetness. In this paper, three different fluorosurfactants FG1105, FC911, and FG40 were evaluated for altering the wettability of sandstone rocks from liquid-wetting to gas-wetting using contact angle measurement. The results showed that FG40 provided the best wettability alteration effect with a concentration of 0.3% and FC911 at the concentration of 0.3%

Research progress and development tendency of polymer drilling fluid technology for unconventional gas drilling

Unconventional gas includes tight sandstone gas, shale gas, coalbed methane, and natural gas hydrate. With huge reserves, unconventional gas has become the most important natural gas resource successor after the end of the “Easy Oil era.” The drilling fluid is an indispensable wellbore working fluid for unconventional gas drilling with multiple functions. The polymer drilling fluid (PDF) is the most common, longest developed, and most diverse drilling fluid type. With advantages of easily controlled rheology, convenient on-site performance maintenance, and specifically low cost and weak environment pollution, the PDF is gradually replacing the oil-based drilling fluid as the first choice for unconventional gas drilling. The invention of the non-disperse low-solid-content PDF in the 1960s shows that PDF technology has entered the stage of scientific development, and until now, its development has generally experienced five stages: beginning, developing, improving, re-developing, and re-improving. Dozens of polymer additives and PDF systems have been invented and applied, which have solved severe drilling problems, greatly improved drilling efficiency, and promoted exploration and development in difficult oil and gas resources. This paper first reviews the research progress of PDF technology according to the timeline by introducing the composition, feature, advantages, and disadvantages of some representative polymer additives and PDF systems, emphatically the function and mechanism of stabilizing wellbores, lubricating drilling tools, and protecting reservoirs of the biomimetic wellbore-strengthening PDF and amphiphobic high-efficiency PDF in unconventional gas drilling. Then, combining future global demands, especially China’s strategic needs of oil and gas exploration and development, the development tendency of PDF technology is critically illustrated by introducing several potential research directions including intelligent PDF, ecological PDF, and PDF for natural gas hydrate and deep layer gas resources

Comprehensive Evaluation of Self-Healing Polyampholyte Gel Particles for the Severe Leakoff Control of Drilling Fluids

Lost circulation has been a serious problem to be solved in many drilling practices during oil, gas and geothermal well drillings. Many materials have been developed and evaluated for the purpose. However, their performance to plug severe leakoff is very limited. Herein, an injectable self-healing hydrogel based on polyampholyte with sulfonated and quaternary ammonium functionalities (P(MPTC-co-NaSS)) was developed and comprehensively evaluated to prevent the severe loss of fluids to formation. By incorporating cation-π (π is for aromatic residues) interaction, the hydrogel shown self-healing property and robustness in severe environment (temperature, salt) by comparison with other hydrogels merely consisting of cation-anion and H-bonding interactions. Aromatic residues enhanced thermal stability above 310 °C. The plugging measurement shown that an addition of 2 wt% dried gel particles can plug high-permeability formation and endure a high pressure of 6 MPa, produce much lower circulation loss and result in a dramatically increased loss volume reduction rate (63.5%) compared with a commercial polymer gel product and an inert material (9.4%) after a self-healing process. Markedly, P(MPTC-co-NaSS) can be used in a wide range of formation temperature (as high as 150 °C) and salt concentrations (NaCl, CaCl2, as high as 15 wt %). In addition to suitable particle size and mechanically robustness, it was also attributed to the soft, swelling, deformable, toughness and self-healable features of P(MPTC-co-NaSS) gel particles as well as the strong adhesion to negatively charged formations in water, even under high thermal and saline condition. These characteristics also contributed to a long-term plugging performance, beneficial to avoid repeated lost circulation in drilling operation. Besides, this self-healing polyampholyte gel particles dispersed well in saline fluid and maintained stable rheological properties after hot rolling, which was favorable to drilling fluid circulation. This study shown the application potential of self-healing materials as plugging material candidate in petroleum drilling industry

A self-breaking supramolecular plugging system as lost circulation material in oilfield

Lost circulation is a frequently encountered problem during workover operations of a low-pressure reservoir. Many lost circulation materials (LCM) have been used to solve the problem, but various disadvantages still exist, for example, oil-soluble materials are easy to get stuck in the pipe string as the temperature drops and gel time and gel strength of the cross-linking gel systems are difficult to control in the occasion of inadequate stirring. A self-breaking supramolecular plugging system used to control lost circulation of workover operations is developed, and it can encounter the aforementioned disadvantages of the traditional LCM. The system forms a space grid structure by non-covalent bonds between the molecules without adding a cross-linking agent. Sand beds plugged with the supramolecular plugging system had a pressure bearing capacity of 4.5 MPa. The self-breaking rate of the supramolecular system was 100% after 7 days at a temperature of 120°C. The core permeability recovery of the self-breaking liquid was 91.9%, indicated that the plugging system is compatible of the reservoir. The supramolecular plugging system has been used in four wells in the Jidong oilfield of East China. Field practice showed that the supramolecular LCM can effectively control lost circulation at different rates during workover operations. The increase in the daily fluid after operations indicated that the slurry has not damaged the reservoir

Research Progress of Elastomer Materials and Application of Elastomers in Drilling Fluid

An elastomer is a material that undergoes large deformation under force and quickly recovers its approximate initial shape and size after withdrawing the external force. Furthermore, an elastomer can heal itself and increase volume when in contact with certain liquids. They have been widely used as sealing elements and packers in different oil drilling and development operations. With the development of drilling fluids, elastomer materials have also been gradually used as drilling fluid additives in drilling engineering practices. According to the material type classification, elastomer materials can be divided into polyurethane elastomer, epoxy elastomer, nanocomposite elastomer, rubber elastomer, etc. According to the function classification, elastomers can be divided into self-healing elastomers, expansion elastomers, etc. This paper systematically introduces the research progress of elastomer materials based on material type classification and functional classification. Combined with the requirements for drilling fluid additives in drilling fluid application practice, the application prospects of elastomer materials in drilling fluid plugging, fluid loss reduction, and lubrication are discussed. Oil-absorbing expansion and water-absorbing expansion elastomer materials, such as polyurethane, can be used as lost circulation materials, and enter the downhole to absorb water or absorb oil to expand, forming an overall high-strength elastomer to plug the leakage channel. When graphene/nano-composite material is used as a fluid loss additive, flexibility and elasticity facilitate the elastomer particles to enter the pores of the filter cake under the action of differential pressure, block a part of the larger pores, and thus, reduce the water loss, while it would not greatly change the rheology of drilling fluid. As a lubricating material, elastic graphite can form a protective film on the borehole wall, smooth the borehole wall, behaving like a scaly film, so that the sliding friction between the metal surface of the drill pipe and the casing becomes the sliding friction between the graphite flakes, thereby reducing the friction of the drilling fluid. Self-healing elastomers can be healed after being damaged by external forces, making drilling fluid technology more intelligent. The research and application of elastomer materials in the field of drilling fluid will promote the ability of drilling fluid to cope with complex formation changes, which is of great significance in the engineering development of oil and gas wells

The transmission mechanism analysis of the impact of economic policy uncertainty on household consumption

Abstract Economic policy uncertainty is proven to have an important effect on household consumption. However, the literature on its transmission mechanism and on comparing the consumption response of urban and rural households, especially in China, is limited. In this paper, we propose two channels through which economic policy uncertainty affects household consumption, the precautionary saving channel and the investment‐employment channel. Then, we use the household survey data (China Health and Nutrition Survey) to explore the heterogeneous effect among urban and rural households. We verify that an increase in economic policy uncertainty can significantly reduce household consumption through both channels. Further, the precautionary saving channel is more important in the urban household sample, while the investment‐employment channel is more pronounced in the rural household sample. In addition, the heterogeneous effect also exists across households in different regions. Our results are robust with consideration of different estimation methods, the lagged effect of the uncertainty, and other characteristics of households

A high-density organoclay-free oil base drilling fluid based on supramolecular chemistry

Abstract: Based on supramolecular chemistry, a rheology modifier CFZTQ-1 for oil base drilling fluids was developed, and an innovative high-density organoclay-free oil base drilling fluid system centering on CFZTQ-1 was designed, evaluated and applied in the field. CFZTQ-1 can strongly increase the elasticity of invert emulsion due to the supramolecular structure assembled in water phase; CFZTQ-1 has stronger effect in elevating the yield point and suspension ability than several foreign rheology modifiers; the synergistic effect with organoclay also makes CFZTQ-1 available in traditional clay-contained invert emulsion drilling fluids. Through the category and dosage optimization of related additives, the formula of the high-density organoclay-free oil base drilling fluid was established and its performance was evaluated. The organoclay-free drilling fluid owns favorable rheology with density of 2.40−2.60 g/cm3, yield point of 13−17 Pa, moderate apparent viscosity and relative low plastic viscosity; after hot rolling at 240 °C, the drilling fluid still keeps a stable performance as its viscosity only increases slightly, its high temperature and high pressure (HTHP) filtration loss is about 10 mL and its electrical stability is greater than 400 V. This innovative drilling fluid system achieves excellent field application as well. Key words: oil base drilling fluid, supramolecular chemistry, rheology modifier, viscoelasticity, drilling fluid performanc

Development of Multiple Crosslinked Polymers and Its Application in Synthetic-Based Drilling Fluids

This study addresses the performance challenges of Synthetic-Based Drilling Fluids (SBDF) in deep wells and high-temperature environments by engineering a novel multiple hydrogen-bonded crosslinked polymer, MBAH/nano-SiO2. Synthesized using methyl methacrylate (MMA), butyl methacrylate (BMA), acrylic acid (AA), N-hydroxyethyl acrylamide (HEAA), and nano-silica (nano-SiO2), the polymer improved crosslinking density, thermal properties, particle size distribution, and colloidal stability. The development of a ‘weak gel’ structure in W/O emulsions improved rheology and electrical stability (ES), with ES values reaching up to 775 V after aging at 180 °C. Moreover, the polymer’s amphiphilic structure and the synergistic effect of nano-SiO2 increased emulsion film thickness and strength, further augmenting stability. The high-temperature and high-pressure filtration loss of SBDF was considerably reduced to 7.6 mL, benefiting well wall stability and reservoir damage control. This study provides crucial insights into optimizing multiple hydrogen-bonded crosslinked strategies and polymers in SBDF applications

Research and Application of New Technology of Bionic Enhanced Wellbore and Strong Lubrication Water-Based Drilling Fluid

After more than a century of development, drilling fluid technology has become capable of dealing with various extreme conditions. As the exploration and development targets shift towards complex oil and gas resources, however, the geological and surface conditions encountered get increasingly complex, which poses a greater challenge to drilling fluid. In this paper, bionics is introduced into the field of drilling fluids, imitating the characteristics, functions, structures, and principles of mussels and earthworms, and a bionic wall-fixing agent with side chains containing catechol functional groups to strengthen the wellbore is prepared. A bionic bonding lubricant that when making the direct friction between the two is changed to the sliding between the membranes is prepared. Compared with the advanced technology introduced from abroad, the strength of the rock is not only reduced but increased by more than 14%, the friction reduction rate is improved by 12.3%. Their mechanism of action and influencing factors are revealed from the macro and micro perspectives. Combined with the formation conditions encountered, other treatment agents are applied to develop a novel technology of bionic strengthened borehole and high lubricity water-based drilling fluid with comparable inhibition and lubricity to oil-based drilling fluid. In comparison with technology, the rate of well collapse is reduced by as much as 82.6%, the accident rate of stuck pipe is brought down by as much as 86.4%, the complication of stuck block is reduced by as much as 79.7%, and the overall cost is lowered by more than 30%. It is truly a safe, efficient, economic, environmentally friendly drilling fluid technology