Abstract:Low temperature or surface cementing often faces problems such as long waiting time of cement slurry，low early strength of cement and slow development. Using calcium nitrate，sodium silicate，comb type polycarboxylic acid drag reducer and polypropylene stabilizer as raw materials，by optimizing the preparation process using solution chemical precipitation method， magnetic stirring and ultrasonic dispersion，a low-temperature strength induced nucleus material（LTI）for cement stone was prepared. The microstructure and elemental composition of LTI were observed by transmission electron microscopy. The influence of LTI on the low-temperature thickening property，static gelling transition time and the development of low-temperature strength of cement was studied. The results showed that the basic unit structure of LTI was stacked tinfoil-like and float-like，accompanied by a small number of rod and regular square crystals，the size of 100—200 nm，and the surrounding extension of fiber-like material. The specific surface area was large. By utilizing its own template nucleation function，nucleus LTI promoted the hydration process of cement，reduced the nucleation potential barrier of accumulated products，and then promoted the transition of low-temperature thickening curve from climbing to right angle. The thickening time ratio could be controlled within 0.47 at 10 ℃. LTI could induce the rapid development of early strength of cement. With increasing LTI dosage and temperature，the low-temperature compressive strength of cement increased. At 20 ℃，the 24-hours compressive strength of cement stone mixed with 1.5% and 5.0% LTI increased by 89.1% and 257.8%. At 30 ℃，the 6-hours compressive strength of cement stone mixed with 1.5% and 5.0% LTI was 4.1 MPa and 6.5 MPa，respectively. Compared with freshly formed cement stone，the compressive strength achieved a leapfrog development. The static gelation transition time of cement slurry mixed with LTI at 30 ℃ could be shortened from 78 min to 18 min，which helped to improve the anti channeling function. Nanoscale hydrated calcium silicate nucleus LTI could shorten the construction cycle of oil and gas wells in low temperature shallow or high cold areas，and then improve the quality of cementing.

Abstract:In response to the challenges of slow development of cement slurry strength and long waiting time for cementing in deepwater/ultra-deepwater cementing operations at low temperature，nano calcium silicate hydrate（CSH）seeds can effectively promote cement hydration rate through crystal nucleation. Nevertheless，CSH tends to agglomerate and leads to uneven particle sizes. Additionally，the dispersants used during the preparation process can delay cement hydration，which does not meet the requirements for low-temperature cementing in deepwater/ultra-deepwater environments. For this reason，a gelatin grafted sulfonated acetone-formaldehyde condensate（SG）was prepared using gelatin，formaldehyde and acetone as raw materials. With SG as the polymer organic dispersion base solution，nano calcium silicate hydrate/gelatin grafted sulfonated acetone-formaldehyde seed crystals（SG-CSH）was prepared by the solution method. The microstructure，hydration exothermic law，hydration products and low-temperature early strength properties of SG-CSH were analyzed through laser particle size analyzer，transmission electron microscope，isothermal calorimeter and X-ray diffractometer，etc. The results showed that SG had excellent intercalation and dispersion ability，which could form a low calcium-silicon ratio（1.0），narrow particle size distribution（3—100 nm），good dispersibility，stable and precipitation free long-term storage seeds with CSH. After adding SG-CSH，more calcium hydroxide and perovskite were generated in the early stage of hydration reaction，accelerating the cement hydration rate. At the same time，the results of cement slurry thickening experiment and compressive strength testing showed that compared with the blank experiment， the thickening time of cement slurry was significantly shortened after adding SG-CSH. The thickening time of cement slurry at 30 ℃ was shortened from 210 minutes to 125 minutes. The compressive strength of cement slurry containing 4% SG-CSH increased by 1.9，1.3 and 5.0 MPa after initial setting for 1 day at 10，15，and 30 ℃，respectively，demonstrating excellent low-temperature early strength performance.

Abstract:In order to improve the high temperature resistance and low damage performance of fracturing fluid thickener，the fracturing fluid thickener （ADAN） was prepared by aqueous free radical polymerization using acrylamide （AM）， methylacryloxyethyl trimethylammonium chloride （ DMC ） ， 2-acrylamido-2-methylpropanesulfonic acid （ AMPS ） and N-vinylpyrrolidone（NVP）as monomers. The preparation conditions were optimized by single factor variable method，the structure and stability of ADAN were analyzed，and then the temperature and shear resistance，resistance reduction，static sand carrying and breaking properties of the fracturing fluid containing ADAN were evaluated. The results showed that the optimum copolymer ratio and reaction conditions were obtained as follows：20% monomer in total mass of reaction system，14∶2∶3∶1 the molar ratio of 4 monomers（AM，AMPS，DMC，NVP），0.4% initiator（K2SO3 and NaHSO3 with mass ratio of 1∶1）in total mass of reaction system，7 pH value，45 ℃ reaction temperature，8 h reaction time. ADAN prepared under these conditions had good thermal stability. The mass loss was about 10% at 40—260 ℃ . The fracturing fluid prepared with 0.8% ADAN，organozirconium crosslinking agent，high temperature stabilizer sodium sulfite and gel breaker ammonium persulfate had good temperature and shear resistance，resistance reduction，static sand carrying and breaking properties. The viscosity was still higher than 90 mPa·s after shearing for 140 min at 200 ℃ and 170 s^-1. In the flow range of 100—160 L/min，the resistance reduction rate increased from 48%to 63% . The settling distance and settling velocity of ceramic particles were 6.3 cm and 0.875 × 10^-2 cm/min after standing in fracturing fluid for 12 h. The residue content after gel breaking was 86 mg/L. ADAN fracturing fluid could withstand the high temperature of 200 ℃，meanwhile the damage to the reservoir was less，which met the needs of field construction and formation.

Abstract:In order to solve the contradictory problem of solubility and cross-linking performance of the existing modified guar gum as a water-based fracturing fluid material，a fracturing fluid thickener dihydroxypropyl modified guar gum（DPHG）was synthesized by reaction of 3-chloro-1，2-propanediol and guar gum. The structure of the DPHG was characterized. The physical and chemical properties of the DPHG and its application performance in water-based fracturing fluids were also investigated. Research results showed that content of water insoluble substances of DPHG could effectively be reduced，the dissolution rate could be increased， and the crosslinking performance with boron crosslinking agents could be improved. In the formulation application of fracturing fluid，DPHG showed better temperature resistance，lower usage and residue content than that of the existing modified guar gum. By optimizing the design of the substitution degree of DPHG，the fracturing fluid could be obtained with temperature resistance of 160 ℃，and the residue content of the fracturing fluid after gel breaking could be reduced to below 20 mg/L，which indicated that DHPG had good application prospect.

Abstract:As a major new field of unconventional oil and gas exploration and development in the future，low-permeability tight oil and gas reservoir is an important force to replace conventional oil and gas resources and support the oil and gas revolution. The nano-fluid displacement in low permeability tight oil reservoir is effective，however，nanomaterials are easy to block micro-nano pore throat，and it is difficult to solve the problems of agglomeration of nanomaterials in aqueous solution. In this study，acrylamide （AM），2-acrylamide-2-methylpropanesulfonic acid（AMPS）and N-12-（2-crotoxyloxy）n-dodecyl-N，N，N-trimethyl ammonium bromide（MEDDA）were used as substrate monomers by the method of free radical copolymerization induced by aqueous solution， the modified nano-SiO₂/polymer displacement fracturing fluid was synthesized by introducing modified nano-SiO₂. The modified nano-SiO₂ displacement fracturing fluid was analyzed and characterized by infrared spectrum，nuclear magnetic hydrogen spectrum and transmission electron microscopy. Then the oil displacement effect of modified nano-SiO₂/polymer displacement fracturing fluid was studied by combining imbibition displacement experiment with nuclear magnetic resonance technology. The results showed that the optimal dosage of modified nano-SiO₂ in polymer system was 1.5%. By comparing the contact angle of different fluids on the core surface，it was proved that the oil displacement efficiency of modified nano-SiO₂/polymer displacement fracturing fluid was achieved by improving the wettability of the rock surface. Compared with the oil displacement fracturing fluid system without modified nano-SiO₂，the spontaneous imbibition efficiency of modified nano-SiO₂/polymer displacement fracturing fluid system was close to 40%，and the imbibition efficiency was increased by more than 1 times. It could also be clearly seen by NMR image that with the increase of imbibition time，the core crude oil saturation in the displacement fracturing fluid with modified nano-SiO₂/polymer was significantly reduced，and the imbibition rate was accelerated，and the imbibition effect was significant.

Abstract:To solve the problems of easy layering，slow dissolution of drag-reducing agents，and significant environmental pollution in the transportation process of conventional white oil-based slickwater systems，the drag reducing agent F4 was selected through measurement of the dissolution and viscosity-increasing properties drag reducing agents F1—F6 with different molecular weights and ionic degrees. By screening thickeners，dispersants，and solid-liquid ratios，a biodiesel-based suspension drag reducer was developed as follows：34.0% biodiesel+3.0% thickener 2#+3.0% dispersant 3#+60.0% drag reducer F4. A variable viscosity and slickwater fracturing fluid system was constructed by combining biodiesel-based suspension drag reducers with clean up additive and anti-expansion agents. The experimental evaluation results showed that drag reducer F4 had good thermal stability with an apparent viscosity retention rate of 33.0% after shearing at 180 ℃ for 2 hours at constant temperature. The variable viscosity and slickwater fracturing fluid had good shear and temperature resistances. The viscosity retention rate could reach over 90% at room temperature and over 50% at 90 ℃ after shearing at the shear rate of 170 s^-1. Among them，the viscosity retention rate of high-viscosity slickwater fracturing fluids could reach over 70%，and the drag reduction rate of low-viscosity slickwater fracturing fluids could reach over 70%. The sand-carrying performance of high-viscosity slickwater fracturing fluids was better than that of low and medium-viscosity fluids，and the minimum settling rate was 0.005272 m/min. The surface tension of the variable viscosity slickwater fracturing fluid after breaking was less than 27 mN/m，the interface tension was less than 2.0 mN/m，the viscosity of the fracturing fluid was less than 5.0 mPa s，and the residue content was less than 50 mg/L，meeting the standard requirements.

Abstract:To solve the problem of high friction of emulsified acid and damage of gelled acid polymer residue in carbonate reservoir stimulation，nanoemulsion was prepared using non-ionic surfactant（tristyrylphenol polyoxyethylene ether），cationic surfactant （quaternary ammonium salt），and cosurfactant（alcohol）as raw materials through pseudo-ternary phase diagram. Then，20% HCl， 5% nanoemulsion，0.1% resistance reducing agent（cationic polyacrylamide），and functional additives were mixed to prepare nano homogeneous phase retarded acid. The properties of the homogeneous phase retarded acid were systematically analyzed and evaluated using rotating rock disc instrument，scanning electron microscope，EDS spectrometer，conductivity meter，particle size analyzer，interfacial tensiometer，wetting angle tester，friction tester，acid-etched fracture conductivity meter，and core flow meter. The retardation mechanism，high acid-etched fracture conductivity mechanism and scale dissolving mechanism were analyzed. The results showed that the nano homogeneous phase retarded acid was a kind of nano homogeneous dispersion system with oil in the inner phase and acid in the outer phase. The particle size distribution was 8—100 nm. It had strong retardation（retarded rate greater than 90%），low friction（friction reducing rate greater than 75%），low viscosity，low damage and high acid-etched fracture conductivity. It could dissolve organic scale and inorganic scale simultaneously. The dissolution rate of asphalt and carbonate rock was 6.91% and 100% ，respectively. It could remove the damage from reservoir emulsification，water lock，and wetting modification. Nano homogeneous phase retarded acid adsorbed on the surface of positive electric limestone by negatively charged nanoemulsion，and then the“isolation barrier”between acid and rock was established to achieve strong retardation. Through differentiated acid-etched and viscous fingering，the high acid-etched fracture conductivity was realized. Through the special oil-water miscible structure of nanoemulsion，organic scale and inorganic scale could be removed simultaneously. The system was successfully applied on offshore oilfields with remarkable effect of increasing production，which was of great significance for the deep treatment of carbonate reservoirs and multiple damage removal.

Abstract:The key to improve the effect of water flooding development of low permeability reservoir is to solve the problem of multi-scale water channeling in low permeability oil fields. An endogenous microbial plugging agent was developed and the formula of the fermentation nutrient solution for the plugging agent has been optimized. Subsequently，the basic physical properties of the plugging agent were characterized through indoor static experiments and the plugging adaptabilities of the plugging agent were evaluated through dynamic core experiments. The fermentation nutrient solution of the strain was consisted of 1.0%—2.0%molasses，0.2% —1.0% sodium nitrate，0.5% —2.0% potassium dihydrogen phosphate，0.2% —1.0% disodium hydrogen phosphate，0.1%—0.5% ammonium sulfate，0.01%—0.1% industrial yeast extract，0.01%—0.03% ferric sulfate and 0.01%—0.03% manganese sulfate. After cultivation in the fermentation nutrient solution for 4 days，the growth of microbial strains stabilized. The formed dispersed particles exhibited a normal distribution with particle sizes of 40—160 μm and a median granularity of about 90 μm. The prepared microbial plugging agent had good shear resistance，salt resistance and stability. The initial state of microbial plugging agent could be injected into the low-permeability core，heterogeneous core and fractured core with good injectivity. The microbial strains could grow and reproduce in the cores based on the characteristics of self-growth，and match with the spatial scale of pore media or fracture media，which could not only plug the porous medium with different scales， but also plug the micro-fractures with different scales. The plugging rate of the core with a permeability of 5×10^-3 μm² reached up to 80%. As for the heterogeneous parallel composite cores with the permeability of 5×10^-3/100×10^-3 μm² and 5×10-3/300×10^-3 μm²，the plugging rate reached up to 92% and 95%，respectively. For the fractured cores with an opening of 30 μm and 80 μm，the plugging rate reached up to 84% and 90%，respectively. The microbial plugging agents could plug both porous medium with the different scales and micro fractures with the different scales based on the characteristics of self-growth，thus possessing the potential to plug the multi-scale water channeling in low-permeability oil reservoir.

Abstract:A study was conducted to address the issue of insufficient injection caused by pressure increase after injection of polymer microspheres into oil and gas field injection wells. By studying the effects of factors such as the dosage of the plugging agent， temperature and time on the viscosity and particle size of the microsphere solution，the working conditions of the plugging agent were optimized. At the same time，the field test was carried out. The results showed that the unblocking agent，composed of 30%JT-1+35% HRJ+22% APG0814+10% H₂O+3% NaCl，could significantly reduce the particle size and viscosity of the microspheres. At the same concentration of unblocking agent，the longer the unblocking time，the better the unblocking effect，and the suitable unblocking time is greater than or equal to 4 hours. The higher the reaction temperature，the better the blockage removal effect. At the same salt concentration，the order of influence on the effectiveness of the unblocking agent was obtained as follows：NaCl≥ KCl＞NH₄Cl. At room temperature，adding 5% unblocking agent into 2% microsphere solution，the viscosity of the microsphere solution was 1.46 mPa s，and the average particle size of the microsphere was 204.6 nm after reaction for 4 hours，compared with the blank sample without the unblocking agent，the viscosity being of 2.17 mPa s and average particle size being of 3243.74 nm，the viscosity of the unblocking solution decreased by 33%，and the particle size decreased by nearly 94%. The solid content in the unblocking residue decreased from 675 mg/L to 70 mg/L，the decrease being of nearly 90%. The surface tension of the residue was 24.89 mN/m，and the interfacial tension was 1.849×10^-2 mN/m，possessing the high surfacial/interfacial activites. The unblocking agent was tested on-site in Changqing and achieved good results in reducing pressure and increasing injection.

Abstract:To address the complex changes in pyrolysis reactions and the difficulty of temperature control in in-situ thermal recovery of oil shale deposits，thermogravimetric analysis experiments were conducted to segment the pyrolysis process of the Chang 7 oil shale in Ordos Basin. X-ray diffraction（XRD）and gas chromatography-mass spectrometry（GC-MS）were utilized to examine the composition of products during the organic matter pyrolysis and exothermic stage. The main chemical reactions evolving at different stages were analyzed to further validate the segmentation. The results showed that the pyrolysis of oil shale under a nitrogen atmosphere could be divided into three stages：dehydration（＜300 ℃），organic matter pyrolysis and exothermic stage（300—720 ℃），and mineral endothermic decomposition（＞720 ℃）. During the organic matter pyrolysis and exothermic stage，the mass loss of oil shale accounted for approximately 74% of the total mass loss，with no thermal decomposition of inorganic minerals. This stage could be further subdivided into three phases：low-temperature initial phase （300 ℃≤T＜450 ℃），mid-temperature pyrolysis phase（450 ℃≤T＜600 ℃），and high-temperature pyrolysis completion phase（600 ℃≤T≤720 ℃）. The primary pyrolysis of organic matter occurred in the mid-temperature phase. As the temperature increased，dehydrogenation reactions of alkanes and esterification reactions transitioned to the thermal cracking of esters and the chain scission of alkanes producing small molecular hydrocarbons. When the temperature rose to 600—720 ℃，compounds tended to polymerize into semi-coke. At the mid-temperature pyrolysis phase， the composition of shale oil was optimal， including 27.70% esters， 29.89% aliphatic hydrocarbons，14.49% alcohols and 12.66% aromatic hydrocarbons. These findings provided theoretical guidance for analyzing the pyrolysis mechanism of oil shale，establishing numerical simulation models for oil shale，and improving on-site recovery rates. They also offered a basis for controlling the reaction temperature range of organic matter to ensure a high conversion rate.

Abstract:Emulsification and viscosity reduction is one of the key techniques for enhancing the recovery efficiency of heavy oil. Due to the inability of conventional viscosity reducers to meet the high temperature and high salinity requirements during thermal recovery of extra-heavy oil，issues such as viscosity reducer deactivation，poor viscosity reduction performance，and low recovery rates often arise. Using nano-SiO₂ sol，amphiphilic dispersant，modifier silane coupling agent，and synergist amphiphilic surfactant as raw materials，a nano-SiO₂ viscosity-reducing oil displacement agent was prepared. The microstructure of the oil displacement agent was characterized. Its viscosity-reducing effect on extra-heavy oil，temperature and salt resistance，adsorption performance， and oil displacement efficiency were evaluated. The results showed that the formula of the oil displacement agent was obtained as follows：50% SiO₂，40% dispersant，4.2% surface modifier and 5.8% synergist. The particle size was about 50 nm with uniform distribution and good dispersibility. The viscosity reduction rate of 1% original oil displacement agent for extra-heavy oil reached 84.99%. After aging for 2 hours at 350 ℃ and a salinity of 15 g/L，the viscosity reduction rate was 83.62%，maintaining 98.39% of its performance. The oil displacement agent changed the sandstone surface from hydrophobic to hydrophilic. Under the condition of 50 ℃，a liquid-solid ratio of 10∶1，and an equilibrium adsorption time of 15 hours，the static adsorption capacity of the oil displacement agent on oil sand was 1.377 mg/g sand. The dynamic adsorption capacity of 1% agent in a packed sand tube was 0.745 mg/g sand，indicating low adsorption loss in the reservoir，which met the requirements for chemical flooding. In a one-dimensional displacement experiment，the oil displacement efficiency of the agent was 26.7 percentage points higher than that of conventional steam flooding. After aging at 350 ℃ for 2 hours，the oil displacement performance retention rate was 97.0% . The nano-SiO₂ viscosity-reducing oil displacement agent had excellent viscosity reduction， temperature and salt resistance， adsorption performance and oil displacement efficiency，which effectively lowered oil recovery costs and then enhanced thermal recovery of extra-heavy oil.

Abstract:The heterogeneous compound system can realize coordination of profile regulation and oil displacement，which has great potential in heavy oil recovery. However，the contribution of its components to oil flooding is not clear，which brings blindness to the optimization and selection of oil flooding system. For a heterogeneous compound system，consisting of partially hydrolyzed polyacrylamide，dual-effect surfactant and branched performed particles gel（B-PPG）），based on the analysis of its interfacial， plugging properties and oil flooding characteristics，flooding experiments of polymer，compound system and heterogeneous compound system were carried out. According to the oil recovery increments obtained by those three types of systems，the contribution of components in heterogeneous compound system on oil displacement under different water-oil viscosity ratios was calculated by normalization. The results showed that a B-PPG sample with initial size of 0.106—0.150 mm（150—100 mesh） behaved a median particle size of 800 μm after expansion. The corresponding heterogeneous compound system matched with a sand pack with a permeability of 1.1 μm²，where its measured resistance and residual resistance factor was 420.5 and 203.0. When a sand pack with lower permeability of 0.3 μm² was encountered，it could not be injected. For a parallel sand pack with a permeability contrast of about 3.0，heterogeneous compound system performed strong profile-control capacity. The maximum injection pressure was 0.42 MPa，and then the maximum fractional flow in low permeability model was 42.2%. While those of the single compound system were only 0.25 MPa and 24.3%，respectively. Under water-oil viscosity ratios of 0.05—0.46，the polymer component made the highest contribution to oil recovery of 43.1%—84.1% in heterogeneous compound system，the surfactant did the lowest of 22.1%—7.6%，while the B-PPG was intermediate of 34.8%—8.3%. At high water-oil viscosity ratios（≥0.46），the contribution of surfactant and B-PPG was small，and the oil recovery potential of heterogeneous compound system after polymer or compound flooding was limited. When the water-oil viscosity ratio（≤0.2）was low，the contribution of surfactant and B-PPG particles got large，and the oil recovery potential of heterogeneous compound system after both water and polymer/compound flooding was great.

Abstract:In order to effectively improve the problem of production decrease year by year due to water injection and gas injection development in fractured-vuggy reservoirs，Tahe oilfield，three equally scaled 3D visual physical models of fractured-vuggy reservoirs were created through 3D printing，including weathered crust，fault-controlled karst，and underground river reservoir models. Subsequently，the microstructure of the black nano-sheet was characterized through TEM and AFM. The oil-water interface adsorption，wetting reversal property and oil displacement effect of the black nano-sheet in three physical models were studied. Based on the actual situation in the field，two types of typical structural unit well groups，such as inter-well and single-well were selected to carry out field pilot tests. The results showed that the average size of black nano-sheet was about 80×60×1.2（nm），and the specific surface area was large. It had good amphipathic property and then could form a stable adsorption layer at the oil/water interface. It had good wetting reversal property and then could change the surface of quartz plate from oil to water. In the 3D models of weathered crust，underground river and fault-controlled karst，black nano-sheet flooding could increase crude oil recovery by 11 percentage point，8 percentage point and 7 percentage point respectively on the basis of water flooding. The weathered crust reservoir had the most obvious benefit effect. Besides，field test results of 15 rounds showed that black nano-sheet flooding was not suitable for single-well replacement production methods in three karst reservoir spaces. The well group composed of weathered crust and underground river karst reservoir spaces had good inter-well connectivity and high acceptance，which was the optimum application area in-situ. In the area，the efficiency was as high as 85.7%，and the oil increase was significant with a cumulative oil increase of about 5000 t. The research results provided on-site guidance and theoretical basis for the subsequent development of black nano-sheet flooding technology in fractured-vuggy reservoirs in Tahe oilfield.

Abstract:In the case of the severe inadequacy in replacing chemical flooding reservoirs currently，there is an urgent need to tackle and break through the technology for enhancing oil recovery in high-temperature and low-permeability oil reservoirs. The smart nano black card oil displacement technology is a highly forward-looking nanotechnology for enhanced oil recovery，which has the potential to significantly enhance oil recovery. According to the condition of high temperature and low permeability reservoir in Henan oilfield，the static performance evaluation of smart nano black card（SNBC）under high temperature condition was carried out，and the oil displacement effect of SNBC under different permeability conditions was evaluated by high temperature core displacement experiment. The results showed that the SNBC had excellent high temperature resistance and good dispersion stability. SNBC could reduce the oil-water interfacial tension to 10^-1 mN/m，and had the ability to change the wettability and emulsify and demulsify rapidly. At the same time，the SNBC had a high efficient oil washing ability. At the temperature of 95 ℃，the injection of 0.3 PV SNBC solution with a mass concentration of 0.005% could improve the recovery rate by 15.8—20 percentage points under different permeability of 50×10^-3 —450×10^-3 μm² in the target oilfield. As a result，the SNBC oil displacement technology is suitable for enhanced oil recovery of high temperature and low permeability reservoirs in Henan oilfield.

Abstract:The preparation of nano oil displacement materials with high interfacial activity remains a critical issue for the application of nanotechnology in ultra-low-permeability reservoirs to enhance oil recovery. The surface interfacial activity of self-made amphiphilic carbon dots（CDs）and high interfacial activity was investigated. The effects of inorganic salts and aging temperature on the interfacial activity of the CDs were studied，and the oil film removal and wettability alteration properties of the CDs were determined. Finally，the oil displacement efficiency of the CDs was evaluated by the core flooding experiments. The results showed that amphiphilic CDs had similar surface tension curves to surfactants，and the surface tension at critical micelle concentration and surface tension was 150.21 mg/L and 28.43 mN/m，respectively. Furthermore，amphiphilic CDs could maintain high interfacial activity at cNaCl =100 g/L and cCaCl₂ =25 g/L，reducing interfacial tension from 0.578 mN/m to 0.032 mN/m and 0.015 mN/m. In addition，amphiphilic CDs had excellent oil film removal efficiency and wettability alteration performance，which could effectively remove residual oil in the form of oil film from the sandstone surface and reduce the contact angle of water droplets in the air from 109.2° to 44.8°. Finally，core flooding experiments showed that the oil displacement efficiency of amphiphilic CDs was 17.4% in the presence of 85 g/L NaCl and 10 g/L CaCl₂. Therefore，as temperature-resistant and salt-tolerant nanoparticles with ultra-small size，amphiphilic CDs have broad application prospects in enhancing oil recovery in high-temperature and high-salt reservoirs.

Abstract:It can more effectively regulate the parameters of application of nano SiO₂ in the field of oil production by understanding the interaction process of Na+ on the surface of nano SiO₂ in saline water. In this paper，the amorphous nano SiO₂ particles was taken as an object of study，so that a nano SiO₂ particle model with both saturated stable silanol groups and deprotonated silanol groups was constructed. By using the molecular dynamics simulation experiments，this paper studied the interaction process between nano-SiO₂ particles and Na+ with different concentrations，including transportation，diffusion，recombination of hydrogen bonds， and the interaction energy. The results showed that in the system of nano-SiO₂ and NaCl solution，when Na+ migrated to a distance of 6.540 ? away from the surface of nano SiO₂ particles，the short-range force began to affect the movement of Na+ . When Na+ migrated to a distance of 2—3 ? away from the surface of nano SiO₂ particles，the charge exchange occurred between Na+ and the surface of nano SiO₂ particles，resulting in an oscillation motion of Na+ . At a NaCl concentration of 3 g/L，most Na+ underwent hydration with water molecules，which could form a stable solvation layer. The interaction between Na+ and nano SiO₂ particles was weak，so Na+ was more likely to diffuse in the solution. As the concentration of NaCl increased to 7 g/L，Na+ could break through the solvation layer. And then Na+ along with water molecules could be adsorbed on the surface of nano-SiO₂ particles. The migration ability of Na+ was weakened，the thickness of the double electric layer on the surface of nano-SiO₂ particles was narrowed，the interaction energy between nano-SiO₂ and Na + was enhanced，and then the stability of nano-SiO₂ was gradually destroyed. The diffusion coefficient of Na+ decreased from 1.39×10-4 ?2/ps to 3.75×10-5 ?2/ps. The thickness of the Stern layer on the surface of nano-SiO₂ decreased from 0.88 ? to 0.72 ?. The thickness of the Helmholtz layer on the surface of nano-SiO₂ decreased from 0.64 ? to 0.20 ?. The interaction energy between nano SiO₂ and Na + changed from -14 000 kcal/mol to -22 000 kcal/mol. The electrostatic interaction between Na + and nano SiO₂ particles was the main force to affect the surface properties of nano SiO₂ particles，while hydrogen bonding and van der Waals forces were secondary forces. The research conclusion could provide a basic theoretical understanding for the application of nano SiO₂ materials in the field of oil and gas drilling and other related industries.

Abstract:Shale reservoirs usually have poor physical properties，small pore throats，while conventional measures such as water injection and chemical injection often fail to achieve good development results. CO₂ huff and puff can not only effectively reduce the oil-gas interfacial tension and the viscosity of crude oil，etc，and then achieve the purpose of improving shale oil recovery，but also inject some CO₂ in the formation to achieve permanent storage，which helps to realize the carbon peaks，carbon neutrality. This article used numerical simulation methods to study the adaptability of CO₂ huff and puff in shale oil. Shale reservoirs were mainly composed of micro and nano scale pore throat systems，which generated significant capillary pressure during fluid flow，affecting the thermodynamic phase behavior of crude oil components and subsequently affecting component calculations and fluid flow in porous media. Therefore，nano confinement effect was introduced into the fluid model to simulate the impact of that on fluid component phase behavior through the changes in critical pressure and critical temperature. At the same time，in order to explore the adaptability of CO₂ huff and puff in shale oil under different ratio of fracture network permeability to matrix permeability（Kf /Km） and oil saturation（So）in the increased production area of fracturing transformation，with the increase of recovery degree and oil change rate as reference indicators，the adaptability charts under different Kf /Km and So were obtained. The results showed that compared to not considering the nano confinement effect，the p-T phase diagram of the components considering the nano confinement effect shifted upwards as a whole，meanwhile the bubble point pressure increased. When Kf/Km was 1000 and the increase in CO₂ recovery rate reached 1.5%，the adaptive limit of So was 0.54. When Kf /Km was 1000 and the increase in CO₂ recovery rate reached 2.0%，the adaptive limit of So was 0.57. When So was 0.500 and the oil change rate of CO₂ huff and puff reached 0.3，the adaptability limit of Kf /Km was 700. When So was 0.548 and the oil change rate of CO₂ huff and puff reached 0.6， the adaptability limit of Kf /Km was 10. The Kf /Km-So charts could be used to determine the physical property limits of shale oil’s adaptability to carbon dioxide huff and puff. The research results had certain guiding significance for the design and application of CO₂ throughput field testing schemes.

Abstract:The J oilfield in Bohai has experienced long-term chemical flooding，and the low permeability part of the injected well reservoir is seriously blocked. The effect of conventional plugging removal measures is poor. It is urgent to develop new plugging remover and plugging removal process. Therefore，taking the backflow blockage of polymer flooding wells in the target reservoir of Bohai oilfield as the research object，the construction，performance evaluation and process research of plugging remover for chemical flooding injection well were carried out. The results showed that the backflow blockage of chemical flooding wells in the target oilfield was composed of 87.77% water，3.83% crude oil，2.76% polymer and 5.64% inorganic scale. The inorganic scale mainly included 59.1% SiO₂，25.9% CaCO₃ and 11.4% MgCO₃，meanwhile contained a small amount of BaCO₃，SrCO₃，BaSO₄， SrSO₄ and Fe₂O₃. According to the composition of blockage，a new type of plugging remover composed of organic solvent， depolymerization agent and scale-dissolving agent was constructed. The preferred organic solvent was a mixture of toluene and n-pentanol（mass ratio of 9∶1—7∶3），the depolymerization agent was 0.5%—1.0% ammonium persulfate，and then the scale-dissolving agent was 5.46% scale-dissolving agent 1（α-cyclodextrin inclusion and β-cyclodextrin inclusion）and 0.54% citric acid. The scale-dissolving effect of three types of plugging remover in turn was better than that of compound dosing method. According to the dosing sequence of depolymerization agent，organic solvent and scale-dissolving agent （mass ratio of 1∶2∶3），the scale-dissolving rate of the blockage was 98.1%. The results of core plugging removal experiments showed that the new plugging remover had a plugging removal rate of more than 80% for inorganic mixed scale and polymer plugging. Compared with single plugging removal operation，the combined operation of inorganic gel profile control and plugging removal had dual effects of “plugging”and“dredging”. The recovery rate was increased by 6.9 percentage points.

Abstract:The demulsification and dehydration was more difficulty with the increasing emulsification degree of polymer flooding produced liquid. Taking the produced fluid of polymer flooding of difficult-to-demulsify and normal demulsification in Shengli Oilfield as the research object，the key factors leading to the increase of demulsification difficulty were analyzed by comparing the properties of oil and water samples，cross emulsification and demulsification experiments and microscopic morphology changes of emulsion. At the same time，the influence of internal factors on emulsification was quantified by referring to the theory of colloidal coagulation. The results showed that the interaction between the high valence metal cations and alkylbenzene sulfonate surfactants was the key factor leading to the difficulty of demulsification. In the cross demulsification experiment，the concentration of high valence metal ions was reduced，and the demulsification dehydration rate of crude oil emulsion was greatly improved. The O/W emulsion was prepared with sodium dodecyl benzene sulfonate as emulsifier. After adding Fe3 + ，the stability of O/W emulsion became worse，and it showed a tendency to change to W/O emulsion.The critical threshold of M of Gudao crude oil emulsion was 214 mmol/kg，and the critical threshold of surface tension was 45 mN/m.

Abstract:The production process of traditional polyether demulsifiers using ethylene oxide and propylene oxide as raw materials is dangerous and complicated，and the demulsification performance is still difficult to satisfy the requirements of actual production. In this paper，an ionic liquid demulsifier BADT-IL for the dehydration of W/O emulsion was synthesized using waste PET plastic as raw material. The chemical structure of BADT-IL was analyzed by Fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance hydrogen spectroscopy （¹H-NMR）， and the effects of BADT-IL concentration， sedimentation time， demulsification temperature，salinity and pH value on the demulsification efficiency of crude oil emulsion were investigated in detail. The demulsification mechanism of BADT-IL in crude oil emulsions was investigated through various methods including the measurements of the interfacial tension （IFT），zeta potential，contact angle （CA），coalescence time，and microscopic observation. The study revealed that the addition of 250 mg/L of BADT-IL to crude oil emulsions containing 70% water content resulted in a demulsification efficiency of 95.23% after static settling at the temperature of 60 ℃ for 180 minutes. Under similar conditions，demulsification efficiency reached 99.22% in crude oil emulsions with 30% water content，producing a clear separated water phase with a clean oil-water interface. BADT-IL demonstrated strong resistance to salt，with the increase of salinity，the demulsification efficiency improved. At a salinity of 50 g/L，the demulsification efficiency of crude oil emulsions with 70% water content reached up to 96.33% . As the demulsification temperature rose，both the demulsification rate and efficiency increased significantly. Compared to typical commercial demulsifiers， BADT-IL exhibited exceptional demulsification performance. BADT-IL could effectively reduce IFT at the oil-water interface during demulsification，replace the emulsifier at the interface，form an unstable composite interfacial film，facilitate droplet coalescence，and consequently ensures efficient oil-water separation.

Abstract:To solve the problem of scaling in the produced water of Huang 3 Chang 6 area，which leads to pipelines and devices blockage and seriously affects the operation of the gathering and transmission stations，the scaling mechanisms in the Huang 3 Chang 6 area was clarified through the analysis of water and scale samples from the gathering station and single well，and targeted scale inhibitors was developed，in addition，the application of the scale inhibitor in the field was mentioned. it was determined that the main reason for severe scale blockage in the Huang 3 Chang 6 area gathering and transportation station was the incompatibility of single well produced water，which leaded to barium strontium sulfate scaling and blockage in gathering and transportation system. A highly efficient barium strontium scale inhibitor，mass ratio of HDTMPA to P-M-P（5000）being of 4∶1，was developed. The inhibition rate of barium sulfate scale was 90.9% when the concentration of the scale inhibitor was 60 mg/L. The indoor applicability evaluation test showed that the scale inhibition rates of the scale inhibitor on the simulated water of the A and B gathering station manifold was as high as 90% and 93%，respectively. the on-site application test of the scale inhibitor showed that the scale inhibitor significantly reduced the scaling degree in the gathering and transmission stations stations A and B，indicating that the application of the scale inhibitor could effectively solve the scaling problem and ensure the long-term stable operation of the Huang 3 Chang 6 area gathering and transmission stations.

Abstract:In order to establish an analytical method of nonionic surfactant of laurel alcohol polyoxyethylene ether used for tertiary oil recovery by high performance liquid chromatography，The best conditions were established by optimizing the chromatographic elements and the method was evaluated consequently. As a result，the chromatographic column was a 15 cm × 4.6 mm hydroxyl column；the mobile phase was consisted of acetonitrile and water using gradient elution（0—3 min：25% acetonitrile/75% water；3—8 min：90% acetonitrile/10% water；8.01 min：25% acetonitrile/75% water）with the flow rate of 1.0 mL/min. Mass detector with positive mode was used for detecting nonionic surfactant and the injection volume was 2 μL. The linear correlation coefficient R was 0.99998 in the concentration range of 20—200 mg/L. The detection limit was as low as 5 mg/L，the spiked recovery was between 88.10% and 97.14%，and the analysis time could be controlled within 10 minutes. The detection method was accurate， sensitive and rapid，and could meet the quantitative detection of lauryl alcohol polyoxyethylene ether in complex production liquid. Moreover，due to the mass spectra being used，the structure of laurel alcohol polyoxyethylene ether in oilfield produced water could be analyzed at the same time of concentration detection.

Abstract:Traditional polymer materials struggle to meet the increasingly complex demands of downhole environments，while inorganic nanomaterials exhibit poor dispersion. Grafting nanomaterials onto polymer chains or embedding polymers into nanomaterials to form polymer nanocomposites can leverage the synergistic effects of both materials to enhance the overall performance of water-based drilling fluids. This paper introduced the application of polymer nanocomposites on improving the rheology，optimizing the plugging and filtration reduction，and enhancing the collapse resistance of water-based drilling fluids，and then summarized their effects and mechanisms. The mechanisms by which polymer nanocomposites improved drilling fluid rheology included polymers enhancing the dispersion of solid nanoparticles in drilling fluid，increasing the internal friction between fluid layers，and forming a spatial network structure through hydrogen bonding and electrostatic interactions between polymers and clay particles. The mechanisms for optimizing the plugging and filtration reduction of drilling fluids involved using inorganic nanomaterials for micropore plugging to form a dense mud cake，while the strong adsorption and amphiphilic properties of polymers created a hydrophobic membrane on the mud cake surface. The mechanisms for enhancing the collapse resistance of drilling fluids included three aspects. First，a dense barrier was formed through nanoparticles bridging and blocking shale nanopores which prevented water molecules from invading the shale. Second，the multifunctional groups on polymer chains formed competitive adsorption on clay surfaces to reduce clay adsorption of water molecules. Third，the combined effects of mature polyamine polymer amino embedding and cationic double electric layer compression strengthened shale hydration inhibition. Challenges of polymer nanocomposites included potential uneven dispersion of inorganic nanoparticles in the polymer matrix during large-scale production. Finally，the paper forecasted the research directions of polymer nanocomposites in three areas，such as reducing wear and drag，reservoir protection，and sustainability.

Abstract:Biosurfactants have strong surface activity，good emulsification，strong antibacterial and antioxidant activity，high stability，good bioselectivity and strong environmental friendliness. Among them，lipopeptide biosurfactants have outstanding properties and are favourable substitutes for chemical surfactants in tertiary oil recovery. Lipopeptide biosurfactants could be divided into cyclic lipopeptides and linear lipopeptides according to whether the amino acids of the peptide chain were connected into a ring. The difference in the types and the arrangement sequence of amino acids in hydrophilic peptide chain，and the difference in the length and the position of branch chain in hydrophobic carbon chain，all resulted in the formation of different lipopeptide structure and biological activity. The mechanism of lipopeptide biosurfactants to improve crude oil recovery was as follows：efficiently reducing oil-water interfacial tension，promoting crude oil emulsification to form large-size micelles，changing reservoir rock wettability，reducing water phase relative permeability，and so on. The results of laboratory experiments and field tests of lipopeptide biosurfactants for crude oil exploitation showed that lipopeptide bio-oil displacement system could effectively reduce the cost of oil displacement agent while obtaining the same effect of enhanced oil recovery as chemical flooding，which confirmed the feasibility for improving crude oil recovery. Nevertheless，the high-yield pathway of lipopeptide synthesis in the upstream，the low-cost purification process in the downstream and the formation adaptability in the actual reservoir were still unclear，which limited the commercialization promotion of lipopeptide biosurfactants in the oilfield.

Abstract:Enhanced oil recovery（EOR）chemicals play a key role in increasing oilfield production and extracting residual oil resources. However，their effectiveness and reliability depend on a series of technical and quality standards. The development trends and compilation process of evaluation standards for EOR chemical agents and the characteristics of current standards for EOR chemical agents domestic and abroad were focused and summarized，the characteristics of these types of chemical agents，and suggestions for future development trends and evaluation standards were analyzed as well. The proposal is to provide a reference and basis for the development direction of standards for chemical agents used for EOR to meet the constantly changing industry needs. By standardizing the quality and performance of these chemicals，their effective application in oilfields can be ensured， thereby increasing oilfield production capacity and reducing potential environmental and economic risks. In the constantly evolving oil and gas industry，standardization will continue to play a key role in providing support and guidance for the industry’s sustainable development.