Abstract:Aiming at the poor effect of traditional vinyl monomer copolymer filtrate reducer in high temperature and high salinity reservoirs，an anti-temperature and salt resistant filtrate reducer for drilling fluids WB-FLA-2 was prepared using the N，N-dimethyl acrylamide，dimethyl diallyl ammonium chloride，N-vinyl pyrrolidone and 2-acrylamide-2-methyl propane sulfonic acid as main raw materials，and the synthetic conditions were optimized by means of orthogonal experiment. The molecular structure and thermal stability of WB-FLA-2 were characterized by means of infrared spectroscopy and thermogravimetric analysis，and the reducing filtration loss of WB-FLA-2 was also evaluated. The results showed that the synthetic condition was optimized as follows： total monomer mass fraction was 20%，monomer mass ratio（DMAA∶AMPS∶DMDAAC∶NVP）was 10∶2∶1.5∶1，the initiator concentration was 0.5%，the reaction time was 5 h and the reaction temperature was 55℃. The synthetic filtrate reducer for drilling fluids was quaternary copolymerization target product and the thermal decomposition temperature was 255℃ . After adding 2% WB-FLA-2 into the fresh water base slurry，composed of 5% bentonite +0.3%Na₂CO₃+fresh water，the API filtration loss（FLAPI）of the slurry decreased from 28.4 mL to 2.8 mL before aging，what’ s more，FLAPI decreased from 78 mL to 7.0 mL after aged at the temperature of 150℃ for 24 h and HTHP filtration loss decreased from 130.8 mL to 36.1 mL at the temperature of 150℃ and under the high pressure of 3.5 MPa. The FLAPI of the brine slurry， composed of 5% bentonite +0.3%Na2CO3+fresh water+ 30%NaCl+2% WB-FLA-2，before and after aged at the temperature of 150℃ for 24 h were 12.4 mL and 14.9 mL，respectively，which indicated that WB-FLA-2 had excellent reducing filtration loss，good thermal stability and salt resistance，and exhibited potential application in high temperature and high salinity reservoirs.

Abstract:During the workover treatment process in western oilfield of the South China Sea，the workover fluid infiltrated into reservoir causing reservoir damage. In order to improve the corrosion resistance of pipe，suppress the hydrate swelling of clay and reduce the permeability of reservoir，a solid-free workover fluid with low damage and low corrosion had been developed. By screening clay stabilizer，drainage aid and weak acid MHA，the optimum prescription of workover fluid system was determined. And the corrosion resistance of workover fluid and the effect on the core permeability were studied. The results showed that the workover fluid system，which was composed of filtered seawater，5% organic salt clay anti-swelling agent TFB-2，0.5% clay anti-swelling agent HAS，1% MHA and 0.5% discharge aiding agent FC310，could effectively inhibit clay hydration expansion and the clay expansion rate of prevention was about 90% which was greater than that of field workover fluid（70%） . The new workover fluid system had a low corrosion rate，and the corrosion rate of steel sheet was 1.2361 g/ （m²·h）at 70℃，only 43.8% of the field workover fluid. New workover fluid could improve the core permeability. The core permeability recovery rate of new workover fluid was about 110%，more than that of field workover fluid（70%） . New workover fluid had a low oil-water interfacial tension and was easy to flow back，which could effectively improve the permeability of reservoir near wellbore area，and the performance was superior to that of field workover fluid.

Abstract:In order to improve the thermo-stability of 2-acrylamido-2-methyl-propane sulfonic acid （AMPS） copolymer and enhance the performance of cement slurry at high temperature，a fluid loss additive，shorted as GP，was synthesized by grafting mixed monomers of AMPS，acrylamide（AM），N， N-dimethylacrylamide（DMAM）and acrylic acid（AA）onto humic acid. The structure of GP was characterized with FT-IR spectroscopy，gel permeation chromatography（GPC）as well as thermogravimetric analysis（TGA） . The effect of temperature on the viscosity of GP solution was studied，and its performance in cement slurry was evaluated at lab scale. The research results showed that the GP was a graft copolymer with a thermal-decomposition temperature of 282℃. Although the viscosity of GP aqueous solution decreased with increasing temperature，its relative viscosities at different temperatures were higher than that of linear polymer LP solution. Compared with their initial values at room temperature，the viscosity retention of GP solution at 90℃ was 66.3%，which was 17.6% higher than that of LP solution. GP had excellent fluid loss control ability and salt-tolerance. The viscosity of cement slurry containing GP（CSG）at room temperature was lower than that of cement slurry containing LP. Moreover，when CSG was heated from 30 to 150℃，its viscosity retention maintained 60.7%，which was 15.8% higher than that of LP cement slurry. GP also exhibited well compatibility with other additives and ignorable effect on the thickening time and compressive strength. The compressive strength of CSG after setting at 50℃ for 48 h was 22.7 MPa，similar to that of LP cement slurry. Ultrasonic experiment revealed that the compressive strength of CSG developed normally. The transition time of static gel strength was 17% shorter than that of LP system，which was benefit to prevent the gas migration during solidifying period of cement slurry.

Abstract:Aiming at the problem that cement sheath integrity was easily broken during construction because of its high brittleness， toughen cement slurry was developed by ethylene vinyl acetate（EVA）copolymer modified by Turker red oil. The effect of modified EVA on general and mechanical properties of cement slurry was studied and the effect mechanism on the mechanical properties of set cement was analyzed. The results showed that modified EVA had good compatibility with cement slurry，its influence on the fluidity and water loss of slurry was less. The thickening time of cement slurry prolonged with increasing modified EVA dosage. Modified EVA had slight impact on the compressive strength of set cement，but it could improve the flexural strength and toughness of set cement. The flexural strength of set cement improved by 4.4% after curing 3 days at 75℃ and the ratio of compressive strength to flexural strength decreased 28.0% when the dosage of modified EVA was 3%. When the dosage of modified EVA was 4%，the elastic modulus of set cement decreased 39.5%. Crystal and polymer generated after hydrolysate of modified EVA combined with hydration products of cement，which made the internal structure of set cement become denser，decreased or removed the stress concentration，prevented crack propagation，and improved the mechanics characteristic of set cement.

Abstract:According to the characteristics of carbonate reservoir of Iraqi Missan oilfields，an acidic completion fluid for protection of carbonate reservoir was prepared using a weak corrosion solid acid HTG as main agent，in which NaCl combined with HCOONa brine was selected to adjust the density of the completion fluid and a corrosion inhibitor JCI was added to control the corrosion of pipe string. The formula of the completion fluid was as follows：25% NaCl + 10% HCOONa + 3% HTG solid acid + 3% JCI corrosion inhibitor. The flushing ability of completion fluid to mud cake formed by drill-in fluid，gel breaking ability，compatibility of completion fluid with the filtrate of drill-in fluid，and the reservoir protection effect of the completion fluid were investigated. The results showed that the corrosivity of the completion fulid was lower，and the mud cake formed by the drill-in fluids could be removed effectively by the completion fluid and the residues of the mud cake could be cleaned up without gel breaking procedure. The permeability recovery of the core，which was polluted by drill-in fluid and then treated by completion fluid，reached over 95%，which indicated that the ompletion fluid had good effects of reservoir protection.

Abstract:To improve temperature-resistant and shear-resistant properties of polyvinyl alcohol fracturing fluid，a modified polyvinyl alcohol fracturing fluid was prepared using the mixture of polyvinyl alcohol and the modified cellulose as thickening agent and organic titanium as crosslinker. The effects of the composition of the thickening agent，the content of the modified polyvinyl alcohol（thickening agent）and the cross linker，temperature and pH value on properties of the fracturing fluid were investigated. The temperature-resistant and shear-resistant properties of the modified polyvinyl alcohol fracturing fluid were compared with that of polyvinyl alcohol fracturing fluid. The results showed that the thickening ability of the thickening agent and the temperature-resistant and shear-resistant properties of the modified polyvinyl alcohol fracturing fluid after adding modified cellulose were significantly improved compared with that of polyvinyl alcohol fracturing fluid. Besides，the properties of the thickening agent with mass fraction of 40% the modified cellulose were optimum. The properties of the fracturing fluid were obviously affected by the composition of the modified polyvinyl alcohol fracturing fluid and pH value. The optimum compositions of the fracturing fluid were as follows：1.8%—2% thickening agent，0.9%—1% crosslinker，and the pH value was in range of 7—9. Under conditions of constant temperature of 120℃ and shear rate of 170 s^-1，the viscosity of the modified polyvinyl alcohol fracturing fluid was still over 50 mPa·s after continuous shearing for 90 min，showing good temperature-resistant and shearresistant properties，which indicated that the odified polyvinyl alcohol fracturing fluid could meet the requirement of fracturing construction when the reservoir temperature was below 120℃.

Abstract:In order to reduce the damage of reservoir stratum caused by fracturing fluid，one method was to reduce the concentration of fenugreek gum in fracturing fluid system. However，traditional method（multiple factors combination test method） was not accurate enough in terms of optimizing low concentration fenugreek gum in fracturing fluid system with high work intensity. In this study，central composite design methodology（CCD）was used to obtain the optimum formula of fracturing fluid. Experiment data was dealt with by mult-variable linear return analysis considering the concentration of fenugreek gum，organic boron crosslinking agent and temperature. Moreover，fracturing fluid systems with low fenugreek gum concentration were optimized based on the established linear regression model and verified by viscosity test at high temperature. The results showed that the viscosity of low concentration fenugreek gum fracturing fluid system could be predicted by the fitting equation. Three factors in fitting equation were arranged according to their influence on gel viscosity in following order：concentration of fenugreek gum＞temperature＞concentration of organic boron crosslinking agent. According to CCD，an optimum formula at 80—120℃ was obtained as follows：0.175%—0.35% fenugreek gum dosage，0.37%—0.73% crosslinking agent dosage. The viscosity of fracturing gel still maintained at 52 to 154 mPa·s after shearing at 1000 s^-1 for 2 minutes and 170 s^-1 for 95 minutes. The CCD provided a good predicting accuracy and the modified system had good temperature resistance and shear resistance.

Abstract:In order to improve the basic performance of xanthan gum and widen its application，cationic xanthan gum（CXG）with bright yellow was synthesised by xanthan gum （XG） and cationic etherification agent （3-chloro-2-hydroxypropyltrimethyl ammonium chlorid）under alkaline condition. The rheological properties of CXG，including shear thinning，viscoelasticity and thixotropy，and the basic properties of CXG solution as fracturing fluid，including proppant carrying capacity，temperature and shear resistance were studied. The results showed that the apparent viscosity of 6 g/L CXG solution was 1.34 times more than that of 6 g/L XG solution. The storage modulus G' and the loss modulus G'' of CXG solution were greater than those of XG solution，and viscoelastic and thixotropic properties were more significant in CXG solution. The descending velocity of ceramsite in CXG solution was much less than that in XG solution. The reserved viscosity of 4 g/L CXG solution was 58.05 mPa·s after shearing at 80℃ and 170 s^-1 for 90 minutes，while the apparent viscosity of 4 g/L XG solution at 30℃ was only 47.53 mPa·s，indicating that the modification of XG enhanced the temperature and shear resistance of XG. Non-linear co-rotational Jeffreys model could be applied to describe the flow curve of XG and CXG solution correctly and the calculated values were in good agreement with the experiment values. Compared with XG，the basic performance of CXG was improved dramatically.

Abstract:In order to improve the effect of water flooding in Ansai low permeability reservoir and determine the microbial limits of injection water，the damage to reservoir caused by saprophytic bacteria（TGB），sulfate reducing bacteria（SRB）and iron bacteria（IB）was studied systematically. The study showed that these three kinds of bacteria widely existed in Ansai injection water and could stably live in the Ansai reservoir water environment，which might result in the expanded potential hazard in the future. The equivalent sphere radius of three types of bacteria were between 0.377 μm and 0.766 μm，which was equivalent to 0.46 times the radius of the hole with the low permeability core，as a result，it was easy to form a stable bridge plug. Flow experiments showed that the SRB was the most harmful bacteria，its concentration should be lower than 10¹ cells/mL，and TGB and IB concentration should be lower than 10² cells/mL.

Abstract:Higher thickener concentration of the conventional guar gum fracturing fluid system had led to higher fracturing cost， high residue content and serious formation damage. Aiming at these problems，multi-core boron crosslinking agent with higher molecular weight was synthesized by borax，polyhydric alcohol and auxiliary solvent. The effect of the addition of guar gum on the viscosity of fracturing fluid was studied，the performance of fracturing fluid was investigated and field application was carried out in Xinjiang oilfield. The results showed that when the mass fraction of guar gum was lower than 0.165% and higher than 0.135%，it could crosslink with DY-1 to form a copolymer. Guar gum fracturing fluid with low concentration had good rheological properties. When the dosage of guar gum was 0.18%—0.4%，the viscosity of fracturing fluid was greater than 100 mPa·s after shearing at 170 s^-1 and 30—140℃ for 1 h. Liquidity index n（0.3—0.7）and consistency coefficient k（1.3—1.8）changed relatively flat at 30—100℃ ，indicating stable performance of fracturing fluid. Fracturing fluid had good static suspended sand property，the sedimentation rate of ceramsite could be reduced to 0.05 cm/min by increasing the pH value of fracturing fluid at 30—80℃ . Fracturing fluid could effectively control fluid loss，and had strong fracture making ability. The gel breaking time of fracturing fluid was 3—4 h at 30—100℃，the viscosity of gel breaking liquid was less than 5 mPa·s and the residue content reduced to 76 mg/L. The cost of fracturing fluid was reduced by 15.2% in field application and the success rate was 100%. The system had obvious effect on increasing oil output，which met the requirement of reservoir stimulation in Xinjiang oilfield.

Abstract:In order to obtain a clean fracturing fluid with low cost and excellent performance，a kind of compound cleaning fracturing fluid（CMV）was developed by compounding quaternary ammonium salt cationic surfactant（CTAB）and sulfonate anionic surfactant（MES），and KCl was used as clay stabilizer. The optimal formula was determined and the performances of the fracturing fluid were evaluated including temperature resistance and shear resistance performance，sand-carrying performance and gel-breaking performance. The experimental results showed that optimal CMV cleaning fracturing fluid composed of 2.5%—3.5% CTAB，2%MES and 1.0%clay stabilizer KCl，was not sensitive to acidity，which could be applied widely. The system showed shear-thickening phenomenon when sheared at low temperature，and the viscosity of fracturing fluid was about 85 mPa·s and 40 mPa·s，respectively，after continuously sheared for 1 h at the shearing rate of 170 s^-1 and at the temperature of 90℃ and 120℃，respectively，hence，the CMV cleaning fracturing fluid was suitable for medium temperature reservoir. The sand-carrying performance of the CMV cleaning fracturing fluid was better than that of 0.3% hydroxypropyl guar gum fracturing fluid，at the sand ratio of 10% in volume and at the temperature of 90℃ ，the falling rate（0.634 mm/s）of ceramsite with 20—40 mush was significantly lower than that in the latter（0.9258 mm/s） . At the temperature of 30℃， the CMV cleaning fracturing fluid could completely break within 3 hours when mixed with different diesel at volume ratio of 1:10—1:5，and the surface tension of the gel breaking fluid was less than 28.0 mN/m，resulting in the anti-discharge capacity increased and the damage to the formation decreased，moreover，the cost of the raw materials of the CMV cleaning fracturing fluid was much lower than that of the most existing clean fracturing fluid.

Abstract:Water channeling due to long-term water flooding led to rapid water cut rise in Bohai S oilfield. Tracer test was used to identify water channeling between oil and water wells，and channeling permeability and pore-throat sizes were calculated. Strength classification of gel profile control system，size classification of polymer microsphere，matching of microsphere size and core throat diameter，and combination of injection slug and crafts were studied. The classified combination of deep profile control technology for deep profile control in Bohai S oilfield was determined. The technology included a combination of the gel（first injecting weak gel and then injecting strong gel） and microspheres，and a combination of gel wellhead profile control and microsphere on-line profile control. The results showed that the permeability of high permeability zone was 8.8 μm² and the average pore throat was about 20 μm in Bohai S oilfield. Two kinds of gel systems which included 0.3% polymer+0.2% crosslinking agent （weak gel）and 0.4% polymer+0.3% crosslinking agent（strong gel）were suitable for the classified combination of deep profile control technology. When the diameter ratio of expanded microsphere and pore throat was 1 to 1.5，the microsphere profile control system had good sealing and migration performance. In the same cost，slug combination that gel sealing high permeability belt near the wellbore and microsphere for deep profile control had the best effect. The space of deep profile control equipment in offshore oilfield was reduced by more than 70% with combination of wellhead and on-line profile control. The effect of field test was remarkable in Bohai S oilfield，using the above selected profile control system could lead to a decrease of 8.4% in water cut and a increase of 18288 m3 in oil production. The classified combination of deep profile control technology was suitable for the deep profile control in offshore sandstone oilfield.

Abstract:In order to solve the difficult water injection of J oilfield due to the high injection pressure，the activate water system， composed of 1×10³—2×10³ mg/L compounded surfactant S005 and 2×10⁴ mg/L clay stabilizer HY-01，was prepared，and the compatibilities with injection water，interfacial tension，anti-swelling property，salt resistance property，heat resistance property and thermal stability of the innovative system was measured. The results showed that the 2×10³ mg/L S005+2×10⁴ mg/L HY-01 activate water system had a great capacity of lowering interfacial tension to ultra-low magnitude（10^-3 mN/m）and the anti-swelling rate of the activate water system to the bentonite was higher than 90%. The activate water system had a certain effect of reducing injection pressure and increasing injection. The activate water system had good scouring resistance，salt resistance and thermal stability. After four times washed out，the anti-swelling rate kept over 85% and anti-swelling retention was higher than 95%. With the increase of NaCl concentration，the oil-water interfacial tension decreased in magnitude，and swelling rate kept stable. With increasing temperature from 55℃ to 82℃，the anti-swelling rate increased and the oil-water interfacial tension kept at ultra-low magnitude. In addition，after aged at the temperature of 82℃ for 30 days，the anti-swelling rate was higher than 90% and the interfacial tension kept at 10^-3 mN/m magnitude.

Abstract:A new kind of plugging technology which combined modified starch hard-gel and ethanediamine was developed in order to improve the development effect of CO₂ flooding in fractured low permeability reservoirs. The plugging effect of the modified starch system，composed of 3% modified starch，3% acrylamide，1% cross-linking agent N， N-methylene bisacrylamide and 0.05% initiator ammonium persulfate，ethanediamine system with mass fraction of 13%，and combination of the modified starch system with ethanediamine system，was investigated，respectively，in the different fractured low permeability cores during CO₂ flooding. Furthermore，the field application effect of combination modified starch system and ethanediamine was mentioned. Under the initial state，the modified starch possessed Newtonian fluid characteristics and could advance steadily in the great rift，and became strong gels after gel-forming and its viscosity was greater than 20×104 mPa·s. The initial viscosity of the ethylenediamine system was close to that of water，and white solid particles or pale yellow viscous material formed after reacting with CO₂. The modified starch gel could block off the open great rift effectively，and the ethylenediamine system could block off the close crack or matrix fluid channeling zone. For the fractured cores with 40 mush，the gas flow rate was reduced from 10000 mL/min to 760 mL/min after plugged by the modified starch gel，and the recovery efficiency could be improved by 21.8%. For the tiny crevice，the gas flow rate was reduced from 1950 mL/min to 330 mL/min after plugged by the ethylenediamine system，and the recovery efficiency could be improved by 18%. For the fractured cores which had no development effect，the recovery efficiency could be improved by over 44% when injecting the starch system and successive ethylenediamine system. Field experimental results showed that when the fractured low permeability reservoirs was gas channeled，the method combining the starch plugging agent and ethylenediamine could greatly improve the recovery efficiency.

Abstract:In order to solve the problem that CO₂ flooding in low permeability fractured reservoir is prone to gas channeling， two-stage Sealing Gas Channeling and Flooding technique，sealing the fracture with the modified starch gel and followed by plugging the high permeability channels with the ethylenediamine，was put forward. the modified starch gel（4% modified starch+4% acrylamide+0.05% crosslinking agent N，N-methylene bis acrylamide +0.18% gelling control agent 4-tert-butylcatechol）and ethylenediamine was chosen as plugging agent of fracture and high permeability channels in matrix，respectively，the sealing and displacement effects of the modified starch gel system on core cracks and ethylenediamine on high permeability channels in matrix was investigated，respectively，and two-stage sealing and displacement experiment of“modified starch gel + ethylenediamine”was also conducted. The results showed that，at 45℃，the sand-filling cracks of the core with the permeability of 0.65×10^-3μm2 could be sealed effectively only by using the modified starch gel. The pressure difference of the core after plugged was substantially constant when CO₂ flooding，the gas flow rate was reduced by 81% and the recovery rate was increased by 25%，which indicated that the modified starch gel had a good plugging strength. The core with relative high permeability of 1.37 × 10^-3μm2 could be plugged effectively only by using ethylenediamine with ethanol protection slug，the gas flow rate was reduced by 85% and the recovery rate was enhanced by 5.3% . However，it was difficult to inject ethylenediamine into the low permeability core without ethanol protection slug. The core of the permeability of 4.5×10^-3 μm2 with sand-filling cracks was sealed with the modified starch gel and then plugged by ethylenediamine，the injection pressure reached 3.5 MPa and 5.6 MPa，respectively，and the enhanced oil recovery was 29.2% and 23.3%，respectively，the effect of the two-stage sealing and displacement was obvious.

Abstract:In order to obtain the composite gel with excellent performance in the supercritical CO₂ state，through the L16（44）orthogonal experiment，the influence of CO₂ pressure，reaction temperature，reaction time and sodium silicate concentration on inorganic gel production were studied. Under the condition of supercritical CO₂，the inorganic and organic composite gel system was prepared from the mixture of sodium silicate solution and acrylamide，the microscopic structure of inorganic gel，organic gel， composite gel was observed through the environmental scanning electron microscopy（ESEM） . The results showed that，The appropriate conditions of inorganic gel were as follows，the reaction pressure was of 9.0 MPa，the reaction temperature was 32.0℃，the reaction time was 14.0 h and the sodium silicate mass fraction was 4.0%. In supercritical CO₂，inorganic gel particle equably dispersed in organic gel network structure，which was beneficial to enhance the strength of the composite gel.

Abstract:Foam alternating CO₂ displacement improved the application effect of CO₂ flooding in heterogeneous reservoir，but high temperature had a great impact on foam stability which reduced the improvement of CO₂ flooding effect by foam. In order to reveal the influence of nano material foam stabilizer on foam properties and displacement efficiency at high temperature，high temperature and high pressure foam evaluation device（improved air flow method）was used. The effects of different foam stabilizers on the foaming properties（20—120℃）and displacement efficiency（95℃）of foaming agent were studied. The results showed that the wetting contact angle of modified nanoparticle was 78° and the average particle size was 29.3 nm. Meanwhile，foam volume was affected slightly by temperature，but the half-life time of foam quickly decreased with increasing temperature. Three types of foam stabilizers，including modified nano material，partially hydrolyzed polyacrylamide（HPAM）and carboxymethyl cellulose（CMC）， could improve the foam stability of foaming agent in high temperature condition，of which modified nano material had the best effect. Oil displacement experiment results showed that adding foaming agent and modified nano material foam stabilizer would significantly enhance the recovery ratio of CO₂ flooding. The enhanced recovery ratio of CO₂ flooding，foam alternating CO₂ flooding and foam flooding adding modified nano material after water flooding was 15.51%，26.94% and 30.93% respectively. Nano material foam stabilizer could improve the stability of foam and the oil displacement efficiency of CO₂ foam system.

Abstract:Horizontal well is the main development way in the shallow complex fault block reservoir of Jidong oilfield. During the process of horizontal well continual production，the water cut go up quickly，resulting in the poor development effects of oil field. The CO₂ huff and puff technology can improve horizontal well productivity and reduce the water cut. In order to optimize the injection-production parameters and improve the effect of the field oil recovery，three-dimensional physical model of CO₂ huff and puff was made of cuttings，the size being of 30 cm×30 cm ×12 cm，the water permeability being of 1.160 μm²，and the porosity being of 31%. The experiment of injection-production parameters optimization，such as injection volume，soaking time and so on，was carried out using the model. The experimental results showed that the effect of increasing oil production was obvious，degree of reserve recovery rose by 1.97%—9.47% more than the development way of depletion and oil exchange ratio was 1.14—3.62 m³/m³.In order to achieve the best effect of increasing oil，the production injection-production parameters were optimized as follows，the rate of injection was 0.3—0.4 PV，the time of well shut was 12—15 h，the velocity of injection was 4—6 mL/min and the liquid withdrawal rate was 480—600 mL/h.

Abstract:In order to study the effect of asphalt deposition on CO₂ flooding in light oil reservoir, based on the indoor experiment method, the CO₂ and light crude oil from Yanchang oilfield was used to study the effect of CO₂ on the regularity of asphaltene deposition, and effect of asphaltene deposition on characteristics of oil-water interface, crude oil composition, reservoir permeability and oil recovery under different pressure and different molar ratio of CO₂-crude oil. The experiment results showed that when the pressure of the CO₂ injection was increased from 0 Pa to 20 Pa, the amount of asphaltene deposition increased from 0.17% to 6.27%, which leaded to a increase of the reservoir permeability damage from 1.87% to 13.64%, and oil/water interfacial tension increased from 2.40 mN/m to 16.80 mN/m. Oil recovery reached to maximum when the pressure was of 25 MPa, being of 11.83%.

Abstract:In order to enhance the oil recovery of medium porosity reservoir in post water flooding of Jianghan oilfield with high salinity，a foam system composed of foam agent and foam stabilizer was developed. The formula of foam system was optimized， by investigating the effect of foam agent type，concentration and the foam stabilizer concentration on foam volume and half-life. The oil resistance，salt tolerance and aging resistance of foam system were evaluated and the injection parameters for foam flooding were optimized. The sealing ability of foam system was investigated through the parallel core displacement experiment. The experiment results showed that the foaming ability of foam system composed of 0.4% foam agent and 0.4% foam stabilizer was good with 110 mL foam volume and 427 min half-life. The interfacial tension between foam system and crude oil was lower（10^-2mN/m）. Foam system had good oil resistance. The half-life was 40 min when the oil content of foam system was 30%. The half-life of foam system was greater than 350 min when the salinity was 300 g/L or the concentration of calcium and magnesium ions was 5g/L，indicating good salt tolerance. The foam volume and half-life changed a little after the foam system aging at 70℃ for 100 days，showing good aging resistance. The optimum injection parameter of nitrogen foam flooding with low interfacial tension was obtained as follows：1.5∶1 gas-liquid ratio，0.4 PV injection volume，1.2 mL/min injection rate. The oil recovery ratio increased 7.51% in single core and 10.04% in dual cores by foam system under optimum conditions. There were better profile modification in Wangchang oilfield with high salinity and heterogeneous oil reservoir.

Abstract:Aimed at the problems of poor stability and worse oil displacement performance of common foam，a xanthan gum-stabilized microfoam with excellent stability and fine particle size was prepared by using a sandpack foam generator with co-flowing gas and foaming solution（5000 mg/L betaine surfactant SL1 + 5000 mg/L xanthan gum）. Stability of the common microfoam（5000 mg/L SL1）and the xanthan gum-stabilized microfoam with the presence of a crude oil was studied and the displacement mechanism was analyzed by micromodel，the oil displacement performance of the microfoam was evaluated by sandpack flooding tests. The experimental results showed that xanthan gum-stabilized microfoam had better oil tolerance than common microfoam did，due to the adsorption of xanthan gum on the surface of the bubble，the absorption of xanthan gum in lamellas increased thickness of the microfoam lamella and inhibited bubble coalescence and liquid drainage. The displacement efficiency strongly depended on the stability of the microfoam，when the microfoam became more stable，the microscopic sweep volume became bigger and the oil recovery efficiency became higher. The main microscopic displacement mechanisms of microfoam flooding for enhanced oil recovery was that direct displacement，emulsification，co-current film flow and counter-current film flow. Xanthan gum-stabilized microfoam flooding increased oil recovery by 22.9%，which was 15.2% higher than that for common microfoam at salinity of 160 g/L and at the temperature of 90℃.

Abstract:In order to satisfy the technical demands of high temperature and salinity reservoirs，the physical properties of a novel polysaccharide polymer（SH-1），including rheology，thickening ability，salinity and thermal tolerance，and flow behavior in porous media，were systematically investigated，and the potential of the SH-1 in enhanced oil recovery（EOR）was evaluated. The experimental results indicated that SH-1 had a superior thickening power compared to polyacrylamide（HPAM）with the relative molecular weight of 8000×104 and hydrolysis degree of 5%，the viscosity of 0.1% SH-1 solution was as much as that of 0.5% HPAM solution，being approximately 100 mPa·s（25℃，10 s^-1）. With the salinity increasing，the viscosity of 0.5% HPAM solution significantly decreased；while it was negligible for 0.1% SH-1 solution，suggesting that the SH-1 had the advanced salt tolerance. With the increase of the temperature，the viscosity of HPAM solution was found to steeply drop，on the contrary，a very slow declining was observed for SH-1 solution，proving its good thermal stability. Under high shear rate，the viscosity loss of SH-1 solution was noticeably smaller than that of HPAM solution，at the shear rate of 20 mL/min，the viscosity loss of HPAM solution was 65%，while in the case of SH-1 this value was only 12%. Meanwhile，the appropriate injectivity and mobility control capability were also confirmed. However，the magnitude of polymer retention of SH-1 was higher than that of HPAM due to the rigidity of polysaccharide polymer chain. It is supposed that SH-1 is very promising for high permeability reservoirs with high temperature and high salinity.

Abstract:Aiming at the characteristic of Lukeqin heavy oil reservoir，including serious geological heterogeneity，unfavorable water-oil mobility ratio，and high formation water salinity，the viscosity，solubility，shear resistance and thermal stability of the hydrophobic association polymer，AP-P8，was researched. The oil displacement performance of AP-P8 was studied，and field application was carried out. The results showed that the viscosity of AP-P8 was significantly better than that of conventional polymers when the preparing water was injection water with 80 g/L mineralization and the temperature was 78℃. The viscosity of AP-P8 solution decreased with the increase of temperature. The viscosity of 2 g/L AP-P8 solution was 64.5 mPa·s when the temperature was 100℃ and the preparing water was injection water. The solubility of AP-P8 was good at room temperature，and the dissolution time was 2.8 h. The retention rate of shear viscosity was 54.2% when the mass concentration of AP-P8 was 2.5 g/L， indicating good shear resistance. With increasing concentration of AP-P8，the core resistance coefficient and residual resistance coefficient increased，which was conducive to improve oil recovery. AP-P8 polymer could increase oil recovery by 10.2% on the basis of water flooding. Field test results showed that the injection of AP-P8 was good with 100 mPa·s solution viscosity at room temperature and 27.5 MPa polymer injection pressure. AP-P8 met the flooding performance requirements of Lukeqin central reservoir conditions，which could be directly prepared by injection water.

Abstract:In order to improve the oil displacement efficiency of chemical flooding in Jidong oilfield，new double anionic surfactants containing a hydrophobic chain and two hydrophilic groups were synthesized with alkyl amine，ethyl acrylate，sodium chloroacetate or sodium 3-bromopropylsulfonate. The structures of the synthesized products were characterized by infrared spectroscopy，thermogravimetric analysis，pH buffer test，and so on. The effect of double anionic surfactant on the interfacial tension between Jidong crude oil and water，and on oil displacement efficiency were studied. The results showed that synthetic surfactants SS-1 and SS-3 contained dicarboxylic acid groups，while SS-2 and SS-4 contained a carboxyl group and a sulfonic acid functional group. Four surfactants could all reduce the interfacial tension between crude oil and water. The interfacial tension reduced to 10^-2—10^-3 mN/m magnitude in the absence of alkali，and that decreased to 10^-4—10^-3 mN/m by SS-1 under weak alkali condition（1% Na₂CO₃）. Weak alkali condition was favorable to improve the oil displacement efficiency of surfactant. The recovery ratio of SS-1 could increase to 13%—15% after water flooding under weak alkali condition. SS-1 could be used as the flooding surfactant for the tertiary oil recovery of shallow oil reservoir in Jidong oilfield.

Abstract:To clarify primary or secondary effect of emulsion and interfacial tension on remaining oil after water flooding in low-permeability reservoir，in view of Jidong oilfield reservoir condition with low permeability，severe channeling and suitable condition for chemical flooding，the system which had greater emulsifying capacity and lower interfacial tension and the other system which had lower emulsifying capacity and higher interfacial tension were selected. Flooding experiments after water flooding with these systems were carried out in the cores with similar permeability. The results showed that two compound systems which met the need of Gao 63-10 block in Jidong oilfield were obtained as follows: 0.2% nonionic surfactant 6501+0.1% anionic surfactant XPS and 0.1% XPS+0.5% NaCl. The former system had great emulsifying capacity and its interfacial tension could reach 10^-2 mN/m. The latter system had worse emulsifying capacity and its interfacial tension could reach 10^-3 mN/m. The enhanced oil recovery of 0.1% XPS+0.5% NaCl system after water flooding was 2.73%，while that of 0.2% 6501+0.1% XPS system was 5.78%. In low-permeability reservoir，oil displacement effect of emulsifying carry and coalescence to remaining oil and residual oil was better than that of interfacial activity. The combination of emulsion and interfacial tension （10^-2 mN/m） could reduce the requirements of interfacial activity which provided experiment basis and technical idea for screening surfactant in surfactant flooding.

Abstract:In order to reveal the aggregation behavior of anionic-nonionic surfactant in oil-water interface，and provide theoretical guidance for the selection and application of surfactant in tertiary oil recovery， the interfacial properties of cardanol polyoxyethylene ether sulfonate（CPES）in decane-water system were studied by molecular dynamics simulation in terms of CPES concentration，temperature，salt concentration and types. The results showed that CPES had excellent interfacial activity. The interfacial tension was 1.83 mN/m when CPES was in saturated solution. The sulfonic group was main hydrophilic group of CPES. CPES had excellent temperature resistance. When the temperature ranged from 298 K to 373 K，the maximum interfacial tension was 16.74 mN/m. CPES had fine salt tolerance. When the concentration of Ca²⁺ increased from 0.10 to 0.35 mol/L，the number of hydrogen bonds between CPES and H2O was almost the same，and the range of interfacial tension was 12.605±1.745 mN/m. Three cations were arranged according to their influence on interfacial property of CPES in following order：Na⁺ ＞Ca²⁺＞ Mg²⁺. CPES had excellent interfacial activity and strong temperature resistance and salt tolerance，which was a good alternative surfactant used in oilfield exploitation.

Abstract:In order to improve the salt resistance of temperature-responsive wormlike micelle system，a wormlike micelle system was prepared using anionic surfactant sodium octadecyl benzene sulfonate（SOBS）and amphoteric surfactant octadecyl hydroxy sulfobetaine（ODAHPS）. The effect of temperature on the viscosity of micelle was studied，and the salt resistance and alkali tolerance of micelle were investigated. The results showed that when the molar ratio of ODAHPS and SOBS was 7，the responsive temperature of micelle was 50℃. The viscosity of micelle increased first and then decreased with increasing temperature. After the responsive temperature was reached，the viscosity of micelle increased with the increase of surfactant concentration. The micellar solution gradually transformed from viscous fluid to elastic fluid with the increase of angular frequency. The viscosity of micelle increased first and then decreased with increasing salt concentration. The micelle system had excellent alkali-tolerance capacity. When the mass concentration of weak base and strong base was 2.5 and 12 g/L，the viscosity of micelle was 133 and 196 mPa·s respectively. This temperature-responsive wormlike micelle system could be used as oil displacement agent.

Abstract:Aiming at ultra-high water cut and high temperature reservoir in IV layers of Shuanghe oilfiled，a study carried out in situ microemulsion flooding with anionic-nonionic and anionic carboxylate compound surfactant B-1 and alkyl sulfonate surfactant A3-2. The oil displacement effect was compared between situ microemulsion flooding and surfactant/polymer binary compound flooding. The distribution characteristics of remaining oil，the microscopic oil displacement efficiency and mechanism of oil displacement in the process of situ microemulsion flooding were also studied by using high temperature and high pressure micro visual simulating technique. The results showed that 3% A3-2 or 3% B-1 solution had ultra low interfacial tension（10^-4 mN/m magnitude）and the property of situ forming microemulsion with crude oil，which had the solubilization parameter up to 20. A3-2 solution could form the middle phase microemulsion with crude oil in situ，and B-1 solution could form the lower phase microemulsion with crude oil in situ. The oil displacement efficiency of situ microemulsion flooding was better than that of surfactant/polymer compound flooding. A3-2 solution had better solubilization capacity and microscopic oil displacement effect than B-1 solution. The situ microemulsion flooding relied mainly on the solubilization between the surfactant and crude oil and formed microemulsion in the porous media，as a result，achieved the effect of miscible flooding. The flooding system could further improve oil recovery with the mechanism of carrying through emulsification，reducing the oil-water interfacial tension，improving core wettability and so on when the crude oil in micellar microemulsion solubilization reached saturation. In this process，clusters and porphyritic of residual oil were firstly removed，and ultimately the various types of remaining oil were effectively removed.

Abstract:On the base of traditional disposal methods of produced water before re-injection in oilfields，such as coagulation and filter，the aeration treatment played a significant role in polymer flooding. In order to establish scientific evaluation method of aeration level in produced water，the reasonable testing method of the dissolved oxygen（DO）was proposed，the relationship between DO and viscosity of polymer solutions prepared by produced water was studied，and how flow conditions affected the oxygen consumption and viscoelasticity was also discussed. The results indicated that the accuracy of colorimetric method depended on the choice of testing tubes. By contrast，the electrochemical probe method performed much better during the water quality analysis. Furthermore，the viscosity of polymer solution increased with increasing aeration of produced water. After the DO in produced water increased from 0.25 to 9.42 mg/L，the viscosity increment could reach 14.88%—19.16%，shear resistance and viscoelasticity of the polymer solutions prepared by the water were also improved in a certain degree. It was obviously that the control of viscosity loss was strengthened when the solution concentration increased. However，the viscoelasticity of polymer solutions was scarcely influenced by the flow conditions of produced water after aeration. The optimum DO in water was about 6 mg/L when the polymer solution was prepared by the produced water in sewage station of Daqing oilfield. The results realized the perfect understanding of the aeration control mechanism from qualitative to quantitative.

Abstract:Accordance with high temperature reservoir conditions of forth oil series of Shuanghe oilfield，the interfactial properties，emulsification property，thermal stability，resistance to adsorption performance and oil displacement performance of surfactant/ polymer（SP）combinational flooding solution composed of the surfactant SH7 and polymer 1630S was evaluated. Experimental results showed that，when the concentration of SH7 was higher than 500 mg/L，the oil-water interfacial tension between SP combinational flooding solution with the 1630s concentration of 1500 mg/L and the crude oil was up to 10^-3 mN/m，and when the concentration of SH7 surfactant was higher than 1000 mg/L，the interfacial tension could be up to 10^-4 mN/m orders of magnitude and reached to ultra-low interfacial tension within 30 min. The emulsifying performance of the 1500 mg/L1630s+2000 mg/LSH7 binary system was good，and the viscosity of emulsion system with oil-water ratio of 7∶3 was 7 times higher than that of the SP binary complex system. The SP binary complex system was resistant to core adsorption，the interfacial tension between SP system after five times adsorption and the crude oil could be still up to 8.82×10^-4 mN/m. Long-term thermal stability of polymer and the SP binary system was good when the oxygen content in the system was lower than 0.8 mg/L，after aging 180 days at the temperature of 95℃，the viscosity of the system was still higher than the initial value，and the oil-water interfacial tension could keep at 10^-4 mN/m orders of magnitude. The homogeneous cores displacement experiment results showed that when injecting 0.606 PV of SP binary composite flooding after water flooding，the oil recovery could be increased by 22.16% on the basis of water flooding ，recovery rate being of 42.26% ，and was 6% higher than that of polymer system at the same concentration. Three times differential permeability experiments showed that the best slug size of the SP system was 0.6 PV，the enhanced oil recovery rate was 16.23%.

Abstract:To expound the effect rules of polymers in chemical flooding systems and active components in oil on the interfacial tension（IFT）reduction by betaine，the influences of partially hydrolyzed polyacrylamide and hydrophobically associating polymer on the dynamic IFT between betaine solution and n-decane were investigated. The influences of oleic acid in n-decane on IFT of betaine solution and betaine/polymer binary systems were studied. The experiment results showed that the hydrophilic part of betaine molecule was larger than hydrophobic part，which resulted in higher IFT against n-decane. The compact film formed by the mixed adsorption of betaine and oleic acid molecules resulted in the decrease of IFT. The addition of partially hydrolyzed polyacrylamide made the dynamic IFT between betaine solution and n-decane increase in general by the formation of mixed films. The interfacial aggregates formed by hydrophobic associated polymer and betaine molecules resulted in the increase of IFT values. The two types of polymers showed similar influence trends on the IFTs between betaine solution and model oil in the presence of oleic acid to those of n-decane.

Abstract:In order to reveal the interaction law between hydrophobically associating polymer（HMPAM）and nonionic surfactant nonylphenol ethoxylate（TX），the apparent viscosity，fluorescence spectra and rheological properties of HMPAM/TX binary system were measured，the interaction between HMPAM and TX with different ethylene oxide（EO）number（4—15）was studied， and the change rule of the interaction was analyzed. The results showed that the change of the macro viscosity of HMPAM/TX binary system was caused by the change of microstructure and quantity of the mixed hydrophobic micro zone and the change of the space network structure in the system. TX series surfactants were arranged according to the interaction strength between HMPAM and TX series surfactants in following order：TX-4＞TX-7＞TX-10＞TX-13≈TX-15. According to the different number of EO，the interaction between the two was divided into three types. （1） When the EO number was 4—7，TX-4 and TX-7 as the representative，it only showed a synergistic effect.（2）When the EO number was 8—12，TX-10 as the representative，it had synergistic effect and“negative effect”.（3）When the EO number was 13—15，TX-13 and TX-15 as the representative，it only showed“negative effect”.

Abstract:A hydrophobically associating polymer flooding agent with high temperature resistance，salt resistance and good solubility in weak alkaline environment was exploited. A alkali-soluble hydrophobically associating terpolymer P（AM/AA/BEM） was synthesized by 2-（2-［4-（1，1，3，3-tetramethylbutyl）phenoxy］ethoxy）ethanol（OP-10）as emulsifier，acrylamide（AM），acrylic acid（AA）and behenyl polyoxyethylene ether methacrylate（BEM）as raw materials. The synthesis condition of P（AM/AA/BEM）was optimized and the performance of polymer solution was studied in detail. The results showed that the optimum reaction condition of P（AM/AA/BEM）was obtained as follows：20% total monomer mass fraction，25% AA mole fraction，0.2% BEM mole fraction， 0.3% initiator 2，2'-azobis［2-methylpropionamidine］ dihydrochloride （V50） mass fraction， 45℃ reaction temperature and 8 hrs reaction time. It showed good thickening property，heat resistance（90℃），salt tolerance（20 g/L）and shear thinning. There was strong synergistic effect between P（AM/AA/BEM）and sodium dodecylbenzenesulfonate（SDBS）. When 400 mg/L SDBS was added in 1 g/L P（AM/AA/BEM），the viscosity of hybrid system increased 3.3 times. P（AM/AA/BEM）showed better thickening property，heat and shearing resistance and salt tolerance than partially hydrolyzed polyacrylamide（HPAM）.

Abstract:In order to improve the effect of demulsification and dehydration of demulsifier，broaden the scope of application，the structure of polyether polyols demulsifier EG-01 and EG-02 was modified by methacrylic acid，the preparation condition of demulsifier was optimized，and the effect of demulsification and dehydration of modified demulsifier on crude oil in Shengli oilfield，Sudan oilfield and Lvda oilfield was studied. The results showed that methylacrylic acid modified polyether synthetic demulsifiers NG-01 and NG-02 had the best dehydration effect under optimum synthetic conditions，6 h reaction time，110℃ reaction temperature，7∶2∶1 mass ratio of methacrylic acid，polyether polyol and tetraethylene pentamine，and 2% amount of benzoyl peroxide of total materials quality. Compared with EG-01 and EG-02，the dehydration rate of NG-01 and NG-02 was faster，and the dehydration effect was better. The dehydration effect of NG-02 with triblock structure was better than that of NG-01 with diblock structure. The dehydration rate of NG-02 on heavy crude oil in Shengli oilfield was more than 90%，and that on medium crude oil in Sudan oilfield and heavy crude oil in Lvda oilfield of CNOOC was more than 95%.

Abstract:In order to obtain a demulsifier suitable for the produced emulsion of WZ11-4 oilfield，A series of polyethers originated from amine initiator was prepared and the effects of sequence of PEO and PPO segments，branch number and PEO content in the polyether demulsifier as well as the solvents on demulsification efficiency were tested. It was found that the diblock polyether had higher demulsification efficiency than that of triblock polyether；the demulsification efficiency increased with the number of branches of the demulsifiers；and there was an optimum PEO content，being of about 25%，at which the polyether exhibited the best demulsification. In addition， the synergism effect between aromatic solvent and polyether demulsifier giving improved demulsification was also found. As compared with polyether dissolved in 95% alcohol，the same polyether dissolved in xylene has much faster dehydration velocity. The industrial two-block polyether demulsifier HYP-105 with PEO content of about 25% that originated from tetraethylenepentamine showed almost the same effect as the incumbent imported one，and could meet the application requirements.

Abstract:In order to solve the problem that the adaptability of visualization techniques in the evaluation of oil displacement agent was not clear，the principles and functions of visual micro displacement model，X-ray computed tomography（CT）and magnetic resonance imaging （MRI） were compared. Furthermore，three kinds of visualization techniques’applications and existing problems in the evaluation of oil displacement agent were summarized. Visual micro displacement model and CT were suitable for the study of oil displacement agent flooding mechanism. The former method focused on the micro analysis，and the latter method focused on the macro analysis. CT and MRI were applicable for the evaluation of oil displacement performance. The former focused on the saturation distribution of residual oil along the way with light oil system，the latter focused on the distribution of remaining oil in different pore size with dilute oil system.

Abstract:The chemical structure and performance characteristics of cross-linker agents（inorganic/organic titanium，zirconium， boron，etc.） commonly used in hydro-fracturing fluid system was described，and the cross-linking mechanisms，technical indicators and field applications of organic boron cross-linker in hydro-fracturing fluid system with hydroxypropyl guar gum as the thickener agent was highlighted. Additionally，as for the aspect of the molecular structures，organic-ligand compositions， cross-linking properties，synthetic routes of different cross-linkers，it was explained that the cross-linking properties was codetermined by coordination center，pH of fracture fluid，ligands，thickener type and concentration. In addition，cross-linkers progress on both theory and field applications was mentioned and the applications status in extreme conditions，performance indicators，composite systems and economic in hydro-fracturing fluid was prospected.