Abstract:In addressing the persistent challenge of rheological control in high-temperature and high-density water-based drilling fluids（WBDFs），a new high-temperature zwitterionic polymer viscosity reducer（HP-THIN）was prepared based on molecular structure optimization design and monomer optimization using orthogonal experiments and single-factor experiments. The molecular structure，thermal stability and relative molecular weight of HP-THIN were characterized and determined by infrared spectroscopy，Ulrich viscometer，and thermogravimetric analysis. The viscosity-reducing ability of HP-THIN on different types of drilling muds such as freshwater mud，salt-containing mud，calcium-containing mud，and high-density composite salt-containing mud was investigated at the temperature of 220 ℃. The effects of HP-THIN on adsorption capacity，zeta potential，and particle size of base-mud clay were tested at ambient temperature and compared with similar commercial viscosity reducers Polythin and xy-27. The results showed that，the optimal reaction recipe of the HP-THIN was as follows，the reaction temperature was 60 ℃ ，thereaction time was 3 h，the amount of initiator and chain transfer agent was 1%（based on the total amount of monomers），and the total mass fraction of the monomer was 30% and the molar ratio of AM，AA，AMPS and PTM was 1.9∶7.5∶2.1∶1. The viscosity-average relative molecular weight of the obtained HP-THIN was about 8211，and the HP-THIN exhibited good thermal stability. After aging at the temperature of 220 ℃ ，the viscosity reduction rates of HP-THIN at the optimal dosage of 0.3% on freshwater-based mud，salt-water-based mud，calcium-containing base mud，and high-density composite salt-water-based mud reached 86%，72%，73%，51%，respectively. Compared to xy-27 and Polythin，HP-THIN demonstrated better high-temperature viscosity reduction effect in all different types of drilling fluid base mud due to its strong adsorption capacity with clay platelets， large absolute value of zeta potential，which was conducive to unentangling the complex polymer network structure between clay particles，significantly decreasing the viscosity of the drilling fluid，showing good application prospects.

Abstract:In order to enhance the plugging performance of oil-based drilling fluids， a hybrid core-shell calcium carbonate-polyurethane well wall reinforcer was prepared via hydrothermal synthesis using calcium chloride，sodium carbonate， glutamic acid，2，4-toluene diisocyanate and dibutyltin dilaurate as raw materials. The effects of well wall reinforcer dosage on the rheological properties，stability and plugging performance of base slurry were investigated by measuring rheological parameters， demulsification voltage，filtration loss and invasion depth. The well wall reinforcer was compounded with some materials such as potassium titanium oxide fibers，sepiolite，diatomite and asphalt oxide. The effects of the compounded well wall reinforcer on the wetting properties，rheological properties，stability，plugging performance，and temperature resistance of the oil-based drilling fluids were studied. The results showed that the well wall reinforcer，with polyurethane as the shell and calcium carbonate microsphere as the core，had a microsphere diameter about 2 μm，exhibited minimal influence on the rheological properties and stability of base slurry，and significantly improved the plugging performance of base slurry. A dosage of 2.5%—3.0% achieved good plugging effects，with a demulsification voltage of 525—542 V and an invasion depth of 0.6 cm. The compounded well wall reinforcer with optimum formula significantly improved the wetting properties of oil-based drilling fluids，had little influence on the rheological properties of base slurry，and helped enhance stability. The demulsification voltage increased to 637 V. The various components of the compounded well wall reinforcer exerted synergistic effects，effectively plugging cracks with different pore sizes，and then exhibited good filtration loss performance. The filtration loss and invasion depth at room temperature were 1.0 mL and 0.2 cm，respectively. After aging at 180 ℃ for 8 hours，the compounded well wall reinforcer still maintained good filtration loss performance. The filtration loss and invasion depth were 3.3 mL and 0.3 cm，respectively，indicating good temperature resistance. The polyurethane soft shell of the well wall reinforcer facilitated the microspheres entry into the leading edge of induced fractures，while the calcium carbonate hard core dispersed stress and prevented further crack extension，effectively plugging the wellbore cracks. Additionally，it exhibited good compatibility with drilling fluids and excellent plugging performance.

Abstract:An acid-soluble weighting agent was prepared using hydroxyapatite as raw material and sodium hexametaphosphate as modifier. The chemical structure of sample was characterized by FTIR. The acid solubility，Zeta potential，and wettability of the modified weighted agent were evaluated. Finally，the influence on the rheology and the filtrate loss of drilling fluids as well as the reservoir protection effect was analyzed. The results indicated that the solubilization rate of the modified weighting agent under 10% HCl solution was up to 88.27%. Drilling fluids with modified weighting agents had good rheology and filtration loss reduction properties. The permeability recovery value of the core contaminated by the drilling fluid mixed with modified weighting agent was ＞90% after soaking in 10% HCl solution for 2 h，which showed that the mud cake formed by the participation of modified weighting agents could be effectively dissolved and removed under the effect of acidic，thus protecting the reservoir.

Abstract:To avoid the use of organic solvents and improve the problem of self-generated proppants easy to aggregate during growth in the well，an environmentally friendly self-generated proppant was designed using styrene（St）and divinylbenzene （DVB）as phase change component，and aqueous solution containing dispersants as non-phase change one. By adjusting the composition and dosage of dispersants in non-phase change component and the speed of pre-mixing of the two phases，the optimum formula and preparation process of self-generated proppant were determined. The morphology and structure of self-generated proppant were analyzed by scanning electron microscope，X-ray diffraction analysis and infrared spectroscopy. Furthermore，its performances were evaluated by particle strength tester and constant load tester. The results showed that，the pre-mixing speed of the two phases was determined to 120 r/min. The dispersants in non-phase change component was polyvinyl alcohol-1788， methylcellulose and sodium dodecyl benzene sulfonate in mass ratio of 5000∶175∶2. When the reaction was standing at a simulation fractures temperature of 100 ℃，the liquid-solid phase transition time of self-generated proppant was 32.5—40.0 min，and then the rapid increase in strength was achieved about 24 min after the phase transformation. The yield of single particle dispersed proppant could reach 78%. Meanwhile，the size of 60% proppant particles could be controlled in 0.850—0.425 mm（20—40 mesh）. The self-generated proppant particles had maximum single particle strength about 32 N，an apparent density of about 1.18 g/cm³，a degree of sphericity of about 0.9 and a low acid solubility of 2.47%. The single particle strength of self-generated proppant was comparable to that of commercially available ceramic proppant，while significantly higher than that of quartz sand proppant. Its acid resistance was significantly higher than that of both. The proposed self-generated proppant and its construction method improved the problems of easy aggregation，low yield and low microsphere formation yield of the self-generated proppant under the absence of shear force. Furthermore，the phase-change solution here did not need to add any organic solvents and is environmentally friendly. It had great potential for deep reservoir exploitation.

Abstract:The adsorption and retention of polymers on the surfaces of oil and gas reservoir rocks play a significant role in the optimization of drilling fluid formulations and enhancing the economic benefits of unconventional oil and gas reservoirs. In this study，the adsorption of partially hydrolyzed polyacrylamide（HPAM），partially hydrolyzed poly（acrylamide/ diallyldimethylammonium chloride）（HPAD），and hydrophobically associating polyacrylamide（HAP）on shale，coal rock，and sandstone surfaces was indirectly measured by starch cadmium iodide method. The adsorption quantities were quantified. The effects of adsorption time，polymer concentration，temperature，and salinity on the adsorption behavior of the three polymers on rock surfaces were analyzed. The results indicated that the adsorption of HPAM and HAP on rock surfaces conformed more closely to the pseudo-second-order adsorption kinetic model，while that of HPAD adhered more closely to the pseudo-first-order adsorption kinetic model. Compared with HPAD and HAP，HPAM exhibited a higher equilibrium adsorption capacity. The adsorption processes of all three polymers on reservoir rocks better fit the Freundlich adsorption model. The time required to reach adsorption equilibrium was closely related to the polymer and the type of reservoir rock. The adsorption of HPAM reached saturation on the surfaces of all three rock types，while the adsorption of HPAD and HAP increased over time. An increase in temperature intensified desorption，resulting in a decrease in adsorption quantity. Conversely，an increase in salinity reduced the solubility of polymers， leading to an increase in adsorption quantity. The continuous adsorption of polymers on reservoir surfaces was the main reason for their consumption in drilling fluids. The sustained adsorption of HPAD and HAP on reservoir rock surfaces might result in the failure of drilling fluids due to their low concentrations.

Abstract:The frequent water gushing in sandstone mining strata of Luohe Formation has seriously affected the safety production of the mine. The traditional grouting systems are faced with the problems of serious percolation effect and uncontrollable gelation performance，which is difficult to achieve effective regulation of fissure water. In this work，the microscopic characteristics of sandstone pores were clarified by analyzing the mineral composition and microscopic morphology of five typical natural core samples， such as gravel-bearing sandstone， giant sandstone， coarse-grained sandstone， medium-grained sandstone， and fine-grained sandstone. A solid-free gel system with low cost and excellent stability was constructed for grouting. The injectivity and plugging performance of the gel grouting system were studied by physical simulation displacement experiment. The pore distribution characteristics in the core before and after grouting were studied by nuclear magnetic resonance online displacement experiment. The results showed that the small pore diameter and poor connectivity were the geological reasons for the difficulty of smooth injection and long-distance migration of the traditional grouting systems. Due to the existence of percolation effect，the curing and plugging effect of traditional grouting system was obviously lower than that of theoretical design. A novel gel grouting system with low cost，solid-free，good injection，and long-distance migration performance was constructed by using 0.5%—0.6% polyacrylamide，0.6%—0.7% organic amine monomer crosslinking agent，0.07%—0.08% phenolic monomer crosslinking agent and 0.2%—0.3% organic acid regulator as raw materials. The gel grouting system could achieve gelation within 48 h，meanwhile， had no obvious dehydration within 180 days，showing excellent long-term aging stability. The gel grouting system had good injectivity. The pressure attenuation ratio was 7.85% —20.95% ，meanwhile，the plugging ratio was 82.04% —92.19% after continuous flooding. The gel grouting system increased the seepage resistance and blocked the subsequent fluid by occupying the large channel or fracture space，which realized the effective plugging of the water layer. The research results could provide new ideas for the grouting and water plugging construction of sandstone in Luohe Formation sandstone.

Abstract:CO₂ flooding is an effective technical measure for tertiary oil recovery in high water cut reservoirs. Using the existing well pattern to inject CO₂ is an economical and feasible development method under low oil price. Although the particle migration caused by the displacement process will block the pore throat of rock，the injection of CO₂ can effectively reduce the injection pressure，and the dissolution occurred during the injection process improves the seepage capacity of fluid as a whole. By carrying out the experiment of particle migration plugging law after CO₂ flooding and the evaluation experiment of CO₂-aqueous solution on rock dissolution，and evaluating the variation characteristics of relative permeability curves before and after displacement，the influence of CO₂ flooding on reservoir seepage capacity was further explained. The results showed that during the injection of CO₂， the injection pressure decreased when the injection rate was 0.1 mL/min and 1.0 mL/min. The core permeability loss was 37.05% after CO₂ flooding under the condition of oil，while the core permeability recovery was 30.48% after cleaning the core with toluene and anhydrous ethanol，indicating that the particles would be bound by crude oil during the migration process，accumulate into clusters，and cause blockage. Although there was a certain blockage，the CO₂-aqueous solution mainly reacted with chlorite and released Ca²⁺，Mg²⁺，Fe²⁺ and other ions. The concentration of Ca²⁺ increased by 137.05%，the concentration of Mg²⁺ decreased by 52.20%，and then the concentration of Fe²⁺ decreased by 49.45%. It showed that although the generated MgCO₃ and Fe₂O₃ would block the pore throat of rock，the dissolution of CaCO₃ by CO₂ was stronger，which improved the seepage capacity of the fluid as a whole，thus improving the water injection capacity and the effect of subsequent water flooding to a certain extent. The irreducible water saturation in the relative permeability curve before and after CO₂ flooding increased，the residual oil saturation decreased，the two-phase seepage area increased，and then the oil displacement efficiency increased. It further indicated that the dissolution produced by CO₂ flooding increased the pore space and seepage channel as a whole，and then improved the injection capacity of injected water.

Abstract:The fracture structure of the Chang 8 reservoir in the Honghe oilfield is complex，which belongs to a low porosity and ultra-low permeability reservoir. The reservoir heterogeneity is strong and the residual oil saturation is high. Because the water phase permeability is low，and the water injection pressure rises rapidly，which exceeds the fracture restart pressure，resulting in serious water channeling and poor effect of water injection development. Combined with the characteristics of nano and microemulsion，a nano-SiO₂ microemulsion depressurization and injection-augmenting system was designed，and the temperature resistance， interfacial tension reduction ability，solubilization and formation compatibility of the system were systematically evaluated，and the core depressurization and injection-augmenting displacement experiment was carried out. The experimental results demonstrated that the nano-SiO₂ microemulsion system not only exhibited excellent temperature resistance and salt resistance but also possessed high interfacial activity，reducing the oil-water interfacial tension to approximately 10^-2 mN/m. The system showed good oil solubilization performance with a solubilization amount of 6.5 mL/30 mL. Simultaneously，the core pressure reduction and injection increase experiment indicated that after injecting 2 PV of 1% the nano-SiO₂ microemulsion system into the cores with the permeability of 0.4 × 10^-3 μm²， the pressure reduction efficiency exceeded above 28% . The depressurization and injection-augmenting effects of the system were evident，meeting the requirements of the field.

Abstract:Nanofluids have become a popular research topic in oil and gas exploration and development due to their potential to enhance oil recovery. the shrinkage behavior of solid-interface oil film was investigated when contacting with 50 mg/L modified lamellar nanofluid in a self-made visualization model. Additionally，oil sand washing experiments were also conducted to determine the oil washing efficiency of the modified lamellar nanofluid at a concentration of 50 mg/L under different conditions. The results showed that the solid-interface oil film shrunk slowly and no wedge-shaped region was observed under simulated formation water condition. However，under the modified lamellar nanofluid environment，the solid-interface oil film shrunk significantly with an obvious wedge-shaped region and two contact lines including an outer contact line and an inner contact line. The shrinkage rate of the outer contact line was 8.5817×10^-5 cm/s while the shrinkage rate of the inner contact line was 0.6617×10^-5 cm/s. The results from oil sand washing experiments exhibited that the oil-washing efficiency of the modified lamellar nanofluid increased with the increase of oil sand particle size and temperature. What’s more，the oil-washing efficiency also increased rapidly at first，followed by a slow increase as the oil sand immersion time was extended，with an optimal immersion time of（8±2）hours. The oil-washing efficiency of the modified lamellar nanofluid could reach as high as 95.7%. These achievements break through the limitation that only high-concentration spherical nanoparticles can form structure disjoining pressure，providing a possibility for the applications of lamellar nanofluid in oilfield and a technical reference for pilot construction processes.

Abstract:Water invasion in carbonate rock gas reservoirs with water can greatly reduce the production. In view of this problem，the surface of carbonate rock was superhydrophobically modified by interface modifier（silane coupling agent）. The influence of interface modification on the percolation ability of water phase，gas phase and gas-liquid two-phase was studied through porous medium flow experiments. The results showed that when the mass fraction of interface modifier was 3%，the contact angle between modified carbonate rock and water was 153°，and then the interface of the carbonate rock reached a superhydrophobic state。Under the condition of superhydrophobic carbonate rock and single-phase constant pressure（0.05—0.40 MPa）injection，the seepage velocity of single water phase was increased by 72.1%—85.9%，and that of single gas phase was increased by 52.9%—72.5%， compared with that before modification（contact angle 0°）. Under the condition of two-phase flow with gas phase constant pressure （0.3 MPa）and water phase constant flow（0.05—0.20 mL/min），the outlet time of sand filling pipe was reduced by 41.0%— 47.4%，and the seepage velocity of gas phase was increased by 102.1%—104.5% . When gas phase and water phase were both two-phase flow with constant pressure（0.07—0.30 MPa），the amount of water phase entering the pores was reduced by 75.6%— 100.0% ，and the seepage velocity of gas phase was increased by 111.1% —200.0% after the interface of carbonate rock was modified to superhydrophobic. By modifying the superhydrophobic interface in the near wellbore zone of gas reservoirs with water， the capillary force of water phase in the pores became resistance. It could effectively prevent formation water from entering the pores of near wellbore zone and reduce the degree of water invasion. At the same time，it could reduce the viscous friction force of gas phase on the pore surface，and then the water phase produced a“slip effect”at the interface，reducing the seepage resistance of gas and water phases，ultimately increasing the production of gas reservoir.

Abstract:Aiming at the limitations of conventional kinetic inhibitors，such as low tolerance to subcooling and short induction time in hydrate formations，a novel kinetic inhibitor P（NVP-g-NVCL-g-DMAEMA）was synthesized from N-vinylpyrrolidone（NVP）， N-vinylcaprolactam（NVCL）and dimethylaminoethyl methacrylate（DMAEMA）. The supercooling degree and induction time in the simulated gas hydrate inhibition processes were used as indexes to optimize the synthetic parameters. The product structure was characterized using infrared spectroscopy，while molecular dynamics simulation software extensively simulated the inhibition process and revealed the mechanism of hydrate kinetic inhibitors. The results showed that the optimum reaction condition was obtained as follows：8∶20∶1 mass ratio of NVP，NVCL and DMAEMA，0.5% initiator（1∶1 mass ratio of ammonium persulfate and sodium bisulfite）in total mass of monomer，65 ℃ reaction temperature and 6 h reaction time. When the mass fraction of inhibitor was 1.0%，the supercooling degree of hydrate formation increased from 2.6 ℃ to 9.6 ℃ under atmospheric pressure， meanwhile the induction time extended from 20 min to 945 min. The inhibition mechanism was mainly driven by inhibiting the formation of hydrate via hydrogen bond adsorption between the carbonyl groups on the five-membered ring or the seven-membered ring of molecular chain，as well as that on the ester group，and the water molecule. Nitrogen atoms on the molecular chain also formed hydrogen bonds and contributed to the adsorption. Furthermore，the steric hindrance of inhibitor also prevented the aggregation of hydrate molecules and thus inhibited the crystallization of hydrate. The kinetic inhibitor not only had active groups that could form hydrogen bonds to enhance the adsorption of inhibitor on hydrate cage，but also had alkyl chains that could affect the movement and distribution of methane molecules，further improving the supercooling degree and prolonging the induction time.

Abstract:To address the issues of poor efficiency of water flooding and low swept volume of chemical viscosity reducers for the conventional heavy oil development，a composite oil displacement system with viscosity reduction and foaming features was developed by using N，N-dimethylamine，sodium 3-chloro-2-hydroxypropane sulfonate and alkyl alcohol polyoxyethylene ammonium sulfate as raw materials. The effects of partially hydrolyzed polyacrylamide（HPAM）on emulsification and viscosity reduction of heavy oil，as well as the effects of polymer，reservoir pressure and heavy oil on the foaming ability and stability of oil displacement system were systematically investigated. The heavy oil recovery of polymer/viscosity reduction composite flooding with and without foam flooding was compared. The results showed that the introduction of HPAM improved the viscosity reduction ability of composite oil displacement systems at the lower concentrations. Under the temperature of 30—80 ℃、mass fraction of 0.3% and an oil-water volume ratio of 7∶3，the composite oil displacement system（referred to as SKY）could reduce the viscosity of heavy oil from 1607 mPa·s to 35.0—60.3 mPa·s，and then reach a high viscosity reduction rate of 96%. Meanwhile，SKY also exhibited excellent foaming performance. The stability of foam was significantly enhanced with the increase of reservoir pressure and heavy oil content. The half-life of foam increased from 8 min to 120 min when the pressure rose from 1 MPa to 13 MPa at 70 ℃. Heavy oil had obvious effect of stabilizing foam. The polymer improved the stability of foam mainly by increasing the viscosity，reducing the drainage rate of foam liquid membrane，and enhancing the strength of membrane. The physical simulation flooding experiments revealed that the polymer/viscosity reduction composite flooding system improved the recovery rate of heavy oil by 10.05 percentage points. After the injection of polymer/SKY and nitrogen，the effect of combination flooding was greatly improved. The produced foam after the injection of gas enhanced sweep efficiency during displacement，so the recovery rate of polymer/viscosity reduction/foam combination flooding was increased by 22.0 percentage points. Therefore，the viscosity reduction/ foam combination flooding technology could realize the integration of viscosity reduction and profile adjustment，which had great application prospects for enhancing heavy oil recovery by water flooding.

Abstract:In order to explore the effect of RhlA and RhlB gene expression on viscosity reduction in microbial oil recovery，a real-time fluorescent absolute quantitative（Q-PCR）method for RhlA and RhlB genes was established，and the Pseudomonas aeruginosa X7 fermentation broth and Karamay Oilfield at different culture stages were detected. The expression levels of RhlA and RhlB genes in different formation waters were measured，and their rhamnolipid production，surface activity，emulsifying activity， emulsifying stability，and crude oil viscosity reduction rate were determined. The results showed that the expression levels of RhlA and RhlB genes were positively correlated with rhamnolipid production，surface activity，emulsifying activity and crude oil viscosity reduction rate. With the increase of fermentation time，the expression levels of RhlA and RhlB genes in the fermentation broth increased continuously and reached the maximum at 24 h，then decreased and stabilized at 60 h，and the maximum expression levels of RhlA and RhlB genes were 2.51 × 10⁶ and 3.25 × 10⁵ copies/μL. The highest expression level of RhlA and RhlB genes reached the maximum value of 824.08 mg/L at 60 hours. The surface activity of the fermentation broth，crude oil emulsifying activity and heavy oil viscosity reduction rate also increased with the increase of fermentation time and reached the maximum value at 24 hours，48 hours and 60 hours，respectively. The rhamnolipid crude extract in the fermentation broth had good stability and could work stably under certain extreme conditions. RhlA and RhlB genes probably affected microbial oil recovery by affecting rhamnolipid production，surface activity，emulsifying activity and viscosity reduction rate of crude oil. This study preliminarily revealed the influence of functional gene expression related to biological surface activity on the viscosity reduction effect of heavy oil，which was important to promote the industrial application of microbial oil recovery.

Abstract:During the injection process into the formation，polymers undergo severe physical and chemical degradation，resulting in significant viscosity loss. In order to reduce the viscosity loss during the polymer injection process，the concept of partially cured polymer oil displacement technology is proposed. At 70 ℃，polymer systems with different viscosities and curing degrees ranging from 60% to 100% were prepared by varying the stirring time of mechanical stirrer. The study investigated the seepage characteristics and oil displacement performance of polymers with different curing degrees in porous media based on macroscopic and microscopic models. The results showed that compared to fully cured polymers，partially cured polymer systems exhibited better viscoelastic properties，enabled better mobilization of residual oil and improved microscopic oil displacement efficiency. Partially cured polymer systems could establish higher resistance coefficients and residual resistance coefficients，and then could retain higher effective displacement viscosities after shearing through porous media. The degree of polymer curing was too low to facilitate the entry of polymers into the deep part of reservoir. In polymer system with curing degree of 60%，the blockage mainly occurred near the injection end of sand-filled tube at 0—1/5 distance，while in polymer systems with curing degrees of 80% and 100%，the blockage mainly occurred near the injection end of sand-filled tube at 1/5—2/5 distance. Compared to water flooding，the incremental oil recovery rates of macroscopic oil displacement for polymer systems with curing degrees of 60%，80% and 100% were 26.2 percentage points，29.0 percentage points，and 23.3 percentage points，respectively. Meanwhile，the incremental oil recovery rates of microscopic oil displacement were 37.3 percentage points，44.9 percentage points，and 36.0 percentage points，respectively. For heterogeneous reservoirs，the residual undissolved polymer particles in partially cured polymers exhibited good plugging and conformance control properties. As a result，the liquid absorption in low-permeability layers was increased，the affected volume was expanded，and thus the recovery rate of low-permeability layers was enhanced. The research results could provide theoretical guidance for field tests of partially cured polymer oil displacement.

Abstract:Aiming at the problem that there is no basis for selecting the molecular weight and concentration of polymer in the process of adopting the binary composite flooding in low permeability reservoir，the laser particle size analyzer is used to test the hydrodynamic dimensions of the binary compound flooding system under different conditions，and the change law of the hydrodynamic diameter of the binary compound flooding system with the molecular weight of polymer，the concentration of polymer，the concentration of surfactant and the mineralization degree of the base fluid was clarified. The average throat radius of cores with different permeability was tested by constant velocity mercury injection experiment，and the empirical formula of artificial core permeability and average throat radius was fitted. based on the injection test results of the binary flooding system and the judgment criteria calculated by the field data，it was clear that when the core permeability was less than 20 × 10^-3 μm² ，the molecular weight of the injected polymer should be less than 3 million and the concentration was less than 500 mg/L；when the core permeability was between 20×10^-3 —40×10^-3 μm² ，the molecular weight of the injected polymer should be less than 5 million. When the core permeability was between 40×10^-3 —70×10^-3 μm² ，the molecular weight of the injected polymer should be less than 12 million. The influence of the salinity of the binding base solution and the concentration of the surfactant on the hydrodynamic size of the binary system could provide guidance for the adjustment of the on-site binary system formula.

Abstract:Spontaneous imbibition is an important method for oil recovery in low permeability reservoirs. There are few reports on the main oil recovery mechanism of microbial enhanced imbibition recovery. In this paper，the patented strains of Brevibacillus potsdamus BS3096 and Pseudomonas aeruginosa LZ3-2 isolated from the reservoir environment in the laboratory were used. Through spontaneous imbibition experiments，the selection of bacteria and medium，the growth conditions of microorganisms，the metabolites of bacteria biosurfactants，the effects of bacteria and other factors on microbial enhanced oil recovery were studied. The experimental results showed that the imbibition fluid containing lipopeptide biosurfactant produced by BS3096 could reduce the oil-water interfacial tension from 0.8848 to 0.2055 mN/m，and the contact angle from 116.4° to 42.8°，so that the wettability of the rock changed from oil wet to water wet. The decrease of oil-water interfacial tension and the change of rock wettability had a significant effect on the recovery of imbibition crude oil. The imbibition recovery of lipopeptide biosurfactant produced by BS3096 could reach up to 60%. The recovery rate of rhamnolipid produced by Pseudomonas aeruginosa PAO1 was 56.26%. The glycoprotein bio-emulsifier produced by LZ3-2 had emulsifying effect on crude oil，and the emulsification rate was 6.96 %. In the imbibition experiment，BS3096 bacteria accumulated in the core，selectively blocked the large pore throat channel，and diverted the imbibition fluid to the small pores in the low permeability area to displace the crude oil，which could increase the recovery rate by 7.5 percentage point. Under the same experimental conditions and surfactant concentration，the order of spontaneous imbibition of biosurfactants and chemical surfactants was biotype ＞ anion ＞ nonionic ＞ cation. The imbibition recovery of lipopeptide biosurfactants was 11.8—44 percentage point higher than that of chemical surfactants. This study provides an efficient，economical and environmentally friendly method for improving oil recovery in low permeability reservoirs，and provides theoretical support for the application of microorganisms and their metabolites in the field.

Abstract:In view of the problem that the production rules of conglomerate reservoirs with different modes in polymer/surface binary composite flooding stage have not fully been studied clearly，the residual oil distribution and pore production features of conglomerate reservoir at different stages of production were studied through indoor core oil displacement experiment combined with NMR online monitoring and CT scanning analysis. The results showed that the oil recovery of the single，dual and complex mode cores in the water drive stage was 31.4%，25.8% and 33.4%，respectively，while the enhanced oil recovery of the dual mode rock was higher than that of the complex mode rock and higher than that of the single mode rock in the binary composite flooding stage，which was 27.9，26.4 and 19 percentage points，respectively. Moreover，the pore limit of oil production was lower than that of the water production stage，and reduction amplitude of the complex mode core was higher than that of the single core and dual core. The heterogeneity of single，dual and complex mode cores was gradually enhanced，resulting in uniform displacement of single mode cores and high oil recovery in the water flooding stage. While the oil in complex mode rock was mainly concentrated at large hole with pore size of 32.7—52.5 μm，which was also largely produced in the water drive stage. In the dual modal conglomerate rock，the oil volume in the large pores was lower than that in the complex conglomerate rock，resulting in that the water flooding recovery rate was lower，and the remaining oil volume was higher. In the binary flooding stage，based on the effect of profile control and flooding and the influence of residual oil after water flooding，the dual mode core had the best effect of enhancing oil recovery，followed by the complex mode core.

Abstract:In order to improve the corrosion problem caused by acidizing fracturing，Schiff base acidizing corrosion inhibitor 1-phenyl-3-（1-cyclohexylamine）-propylene（PCP）was synthesized by cinnamaldehyde and cyclohexylamine. Its structure was characterized by infrared spectroscopy and gas chromatography-mass spectrometry. The corrosion inhibition effect of PCP was evaluated by weight loss method，electrochemistry（polarization curve，impedance spectrum，noise）and molecular dynamics simulation. The results showed that the synthesized product was the target product PCP. Under the condition of 15% HCl and 90 ℃， and with the increase of PCP concentration，the weight loss corrosion rate and corrosion current density of J55 steel decreased significantly，while the corrosion inhibition efficiency increased gradually. The corrosion inhibition efficiency could reach more than 99% under different PCP dosage，indicating good corrosion inhibition effect. When the dosage of PCP reached 0.15%，the overall corrosion rate and corrosion inhibition efficiency had little change with increasing concentration of corrosion inhibitor. That is，the adsorption concentration of corrosion inhibitor on the surface of J55 steel had reached the critical micelle concentration，so the adsorption amount did not change. PCP was a mixed corrosion inhibitor，which inhibited both cathode hydrogen evolution and anode dissolution reaction. With the increase of PCP concentration，the arc radius，polarization resistance and noise resistance were all arranged from small to large in following order：blank＜0.05%＜0.10%＜0.15%＜0.20%. The low frequency white noise level decreased with the increase of PCP concentration in the current PSD diagram. That is，the corrosion rate of J55 steel decreased continuously，which was consistent with the rule of weight loss method and polarization curve reaction. When PCP molecule adsorbed and balanced with the metal，the whole corrosion inhibitor molecule was in the same plane，and then adsorbed on the J55 steel surface in parallel to achieve complete coverage，thus effectively slowing down the immersion of corrosive medium.

Abstract:The depth of Xushen gas field is greater than or equal to 3000 m，the well temperature is less than or equal to（le） 150 ℃ ，meanwhile，the climate character is long wintertime and low temperature. Aiming at these characteristics，the anionic surfactant palmitamide sulfobutyrate disodium （ASB-16A） was synthesized using maleic anhydride，cetamide and anhydrous sodium sulfite by two steps of amidation and sulfonation reaction. ASB-16A was mixed with foaming agent lauryl-glucoside （APG1214），antifreeze ethanol，and deionized water to prepare a bubble agent （CYY-1） with cold and high temperature resistance. The foam performance，high temperature resistance，low temperature stability and compatibility with formation water of CYY-1 were evaluated. Finally，CYY-1 was applied in Xushen gas field. The results showed that the optimum formula of CYY-1 was obtained as follows：10% ASB-16A，10% APG1214，44% ethanol，and deionized water. CYY-1 showed better foaming and steady blebbing properties. At 80 ℃，1.25% CYY-1 solution had an initial foam height of 150 mm，a foam height of 150 mm and 75 mm for 3 min and 5 min standing time，respectively，and a liquid volume of 1100 mL. The aging under weak base conditions， such as 8.5 pH value，150 ℃ and 24 hours，had little effect on the foam performance of CYY-1. The stability at low temperature of CYY-1 was better than that of commonly used low temperature bubble agent. After freezing at -35 ℃ for 7 d，CYY-1 became cloudy. But it could still flow in the pipeline，which met the requirements of automatic filling of device. The compatibility of CYY-1 with formation water was good. 0.5% —10.0% solution was still clear and transparent after standing for 48 hours at room temperature，so automatic bubble filling could be implemented. Two wells were tested in the field. The daily gas production of one well increased from 2.46×10⁴m³ to 3.07×10⁴m³. Meanwhile，the daily water yield decreased from 5.77 m³ to 3.70 m³. Stable carrying water production was achieved. CYY-1 was suitable for foam drainage gas production of well temperature le 150 ℃，salinity le 16 g/ L and pH value of 8.5.

Abstract:The scale plugging problem is one of the main problems causing the production reduction of oil and gas fields. The common acid deplugging agent is highly corrosive，which affects the safe production of oil and gas wells. In order to solve the above problems，the HOMO/LUMO level and binding energy of chelating agents with metal ions were calculated by using Gaussian 09 software to optimize the molecular structure of several chelating agents. The chelating agent diethylenetriamine pentaacetic acid（DTPA）was selected. At the same time，computational chemistry was used to explore the mechanism of the compound detergent，and the synergistic effect between different additives was studied. On the basis of theoretical research，a non-acid scale removal agent system with DTPA as the main agents was developed：12% DTPA+0.3% scale inhibitor PASP+0.4% penetrant JFC. The scale dissolution rate of the system could reach more than 80% for a certain site scale sample，exhibiting good scale dissolving effect. According to the kinetic simulation，it was verified that the dissolving process of calcium carbonate by the descaling agent system conformed to the quasi-second-order kinetic model.

Abstract:In order to analyze the polymerization process of maleic anhydride（MA）and sodium allyl sulfonate（SAS），two variables were designed，such as neutralization degree and initiator dosage，while the formula and process remained basically unchanged. A series of MA/SAS samples were synthesized by changing one of the variables，and then were characterized by nuclear magnetic resonance spectrometer and gel permeation chromatograph. The results showed that the copolymerization activity of MA and SAS was good. When the neutralization degree did not exceed 100%（relative to the mole percentage of MA），a small amount of initiator （2.4 g sodium persulfate） would cause a high monomer conversion，but 6% —8% of the monomers remained unpolymerized. The type and quantity of remaining monomers were closely related to the neutralization degree and initiator dosage. MA was partially hydrolyzed into maleic acid in aqueous solution. Although the amount of maleic acid was relatively small，it could make a bimodal molecular weight distribution of the copolymer as a relatively poor polymerization activity. Adding alkali could neutralize maleic acid. When the neutralization degree did not exceed 100%，maleic acid mainly became a monosodium maleate with good polymerization activity，indirectly promoting the polymerization of MA monomers. When the neutralization degree was 200%，maleic acid mainly turned into disodium maleate，which had relatively poor polymerization activity and seriously hindered polymerization. When it was not neutralized or the neutralization degree was 100%，it took 7.0—7.2 g of initiator to convert all the monomers. At an appropriate neutralization degree（about 20%），a small amount of initiator（4.0—4.2 g）was needed. A more completely polymerized copolymer could be obtained，saving about 40% of the initiator dosage. The static scale inhibition performance of calcium carbonate，calcium phosphate，and calcium sulfate was studied using MA/SAS copolymers synthesized under optimum conditions. The copolymers showed excellent inhibition of calcium phosphate scale and calcium sulfate scale，as well as good inhibition of calcium carbonate scale. The corresponding maximum scale inhibition rates were 94.38%，100.00% and 59.03%，respectively.

Abstract:Aiming at the wettability evaluation of fracturing oil displacement agents in low-permeability tight reservoirs，the error and uncertainty of the existing contact angle method were analyzed. An improved method for evaluating the wettability of fracturing oil displacement agents was proposed. The wettability tendency index，i.e.，the ratio of wetting contact angle between oil displacement agents and distilled water on the hydrophilic/lipophilic surfaces，was used to characterize the wettability change direction and degree of fracturing oil displacement agents. The results showed that there was some uncertainty in reflecting both the direction and ability of the oil displacement agent to change the reservoir wettability by the contact angle and the maximum value of the contact angle change. Hydrophilic surfaces were very stable and had small deviations in wetting contact angle，while lipophilic surfaces had large deviations in wetting contact angle. The relative average deviations of the wetting contact angles between distilled water and hydrophilic/lipophilic surfaces were 0.281% and 8.929%，respectively. In addition，the differences in the maximum change values of contact angles of some oil displacement agents on hydrophilic/lipophilic surfaces were not obvious. The wettability change degree of oil displacement agents could be better characterized by wetting tendency index. The uncertainty of wetting tendency index was much smaller than that of contact angle. The uncertainties of contact angle（wetting for 30 s）of 0.2% sulfonate oil displacement agents，polyoxyethylene ether oil displacement agents and fluorocarbon oil displacement agents on hydrophilic surfaces were 1.24，3.11 and 0.64，respectively，while their uncertainties of water wetting tendency index were 2.48×10^-2，6.33×10^-2 and 1.76 × 10^-2，respectively. The water-wetting index of natural rock samples under the effect of seven fracturing oil displacement agents was measured by the Amott method. The order of this water-wetting index from largest to smallest was consistent with the order of water-wetting tendency index from smallest to largest measured by the contact angle method. The test results of both methods further confirmed the accuracy and superiority of wetting tendency index. This method was beneficial for quickly evaluating the ability of fracturing oil displacement agents to change reservoir wettability and for preferentially selecting fracturing oil displacement agents for low-permeability tight reservoirs.

Abstract:Polymer microspheres drive conditioning are one of the main techniques to improve water drive effectiveness. The transportation in formation and effectively detection in extracted water of microspheres will directly affect the modulation drive. So the fluorescent carbon dots were introduced into the microsphere drive conditioner to play the role of tracer. The fluorescent core-shell microspheres drive conditioner formed from a mixture of core microsphere solution containing fluorescent carbon dots and shell layer aqueous solution. In order to reduce the interference of impurities in the extracted water after oil-water separation on the effective detection of core-shell fluorescent microspheres，the feasibility of the method was verified by firstly performing a linear fitting between the concentration of fluorescent microspheres and fluorescence intensity. Then the extracted water was adsorbed by silica gel. The practicability of silica gel adsorption was verified by comparing the fluorescence emission spectra of the extracted water before and after adsorption. Finally，the fluorescent microspheres prepared from the extracted water were adsorbed with silica gel，and then the standard curve of fluorescence intensity and microsphere concentration was plotted. The results showed that at the excitation wavelength of 347 nm，there was a good linear relationship between the mass concentration of fluorescent microspheres and the fluorescence intensity at the emission wavelength of 445 nm，with the correlation coefficient of determination （R²）of 0.9870. The fluorescence intensity of the water-driven extracted water was significantly reduced after silica gel treatment. The silica gel adsorption could effectively remove the impurities in extracted water. At the excitation wavelength of 347 nm，the fluorescence spectrometer slit of 10—20 nm，and the mass concentration of microspheres from 1 to 1200 mg/L，the mass concentration of fluorescent core-shell microspheres in aqueous dispersion （x） was positively and linearly related to the fluorescence emission peak at 462 nm（y）. The fitted equation was y=2497.1042+3.1847x，with R² of 0.9972，which had a high confidence level. The linear phase between the fluorescence intensity and the concentration of core-shell microspheres could meet the requirements of field detection. The method could provide a reference for the quantitative detection of fluorescent microsphere content in similar reservoirs.

Abstract:As conventional oil reservoirs enter the“double high”stage of high production and high water content，the availability of remaining reserves decreases and then the difficulty of stable oil production increases. To tap the remaining oil in reservoir for a long time，it is necessary to strengthen the characterization and understanding of the distribution of remaining oil. By combing the core analysis，one-dimensional core oil repulsion and microscopic oil repulsion experiments carried out at home and abroad for different reservoirs，and combining the techniques of laser confocal，nuclear magnetic resonance imaging，CT scanning imaging and fluorescence analysis，this article comprehensively summarized the research methods on the distribution of one- to threedimensional microscopic residual oils from qualitative to quantitative. The results showed that the oil-bearing thin section analysis was the basic experimental method to study the distribution of residual oil with high retention of the residual oil distribution state， which could truly reflect the characteristics of residual oil and was mature. The traditional core driving model was an indispensable experimental method for the study of the residual oil distribution law and the mechanism of improving recovery，which was the most reflective of the real reservoir situation. But it could only analyze the influence of different factors on the permeability effect from the macroscopic point of view. The real core visualisation model could effectively make up for the shortcomings of traditional core oil repulsion model. But the visualisation experimental device had limited resistance to high temperature and high pressure. Meanwhile，the production cost was high，and the image processing was not very clear. Microfluidic control model，as an emerging technology，had controllable parameters and high experimental reproducibility. At the same time，it could display the microdrive process and the flow of fluids visually under various oil repulsion modes，which could provide a new way of evaluating the effect of oil repulsion. However，there was still a certain gap between the simplified microscopic porous model and the results of actual displacement experiments. The imaging analysis technology mainly based on nuclear magnetic resonance imaging technology and X-ray CT imaging technology，with their respective advantages，combined with the real core experiments，had become an important means of effectively describing the characteristics of residual oil distribution from a microscopic perspective. This review provided important references for researchers to understand the existing research methods for remaining oil，and then provided theoretical support for the study of remaining oil distribution，efficient development，and improved oil recovery in different types of reservoirs.

Abstract:Crude oil contains natural surfactants such as asphaltenes，resins，naphthenic acids，fatty acids，microcrystalline waxes， and interfacial active solid particles. During extraction，the shearing，compression and agitation within formation pores，wellbores， nozzles and pipeline valves，along with the addition of surfactants and water in oil displacement agents，as well as pump pressure and pipeline turbulence during collection and transportation，can easily form stable crude oil emulsions. Crude oil emulsions not only cause corrosion in pipelines and pumps and reduce pipeline transportation efficiency，but also lead to catalyst poisoning during downstream refining processes. Chemical demulsification，due to its high efficiency，rapid action，simple equipment requirements， and low energy consumption，is a commonly used method for the efficient separation of crude oil emulsions. Ionic liquids（ILs）are effective demulsifiers due to the advantages such as non-flammability，good thermal stability，recyclability，and low vapor pressure. By summarizing the characteristics of ILs and their current application as chemical demulsifiers，this paper discussed the demulsification mechanisms and factors influencing demulsification performance. It identified issues with the practical application of ILs demulsifiers，and then suggested future research directions. ILs were suitable for demulsification under harsh conditions such as high salinity，high temperature，and high viscosity（e.g. extra-heavy oil）. Demulsification mechanisms included adsorption， replacement and ion exchange. Factors affecting demulsification effect included the type and concentration of ILs，relative molecular mass，salinity，temperature，and emulsion type. By selecting appropriate ILs and their dosages，and determining optimum treatment conditions，demulsification efficiency could be enhanced. Although there were still significant challenges and key issues preventing large-scale application of ILs demulsifiers，the development of low-toxicity or non-toxic，low-cost， low-viscosity ILs and their use in conjunction with nanoparticles，and polymer ILs remained highly significant.

Abstract:The new national standard GB/T 7713.2—2022“Presentation of academic papers”partially replaces GB/T7713—1987 “Presentation of scientific and technical reports，dissertations and scientific papers”，which has been implemented on July 1，2023. Good learning and implementation of the new national standard is of great significance to the standardization of academic papers preparation and publication，so as to facilitate the retrieval and dissemination of academic papers and promote the exchange and use of academic achievements. When learning“Presentation of academic papers”，it should pay attention to the difference between requirements，recommendations，permits and statements. The auxiliary verbs used in each clause should be distinguished. Combined with the characteristics of oil and gas industry and the actual editing work，this paper analyzed the common non-standard problems in title，abstract，keyword，text part，quantity and unit，table，number and mathematical formula. Authors and editors should pay more attention to the standardization，which helped to improve the standardization level of academic paper writing and editing.