Abstract:Rheological modifier was a key additive to enable flat rheology property for water-based drilling fluids. A specific rheological modifier was synthesized by reverse microemulsion method using acrylic acid （AA），acrylamide （AM） and 2-acrylamido-2-methyl-propane sulfonic acid （AMPS） as raw materials. The structure，morphology and thermal stability of synthesized product were characterized. Meanwhile，the rheological behavior of rheological modifier and traditional viscosifier in water-based drilling fluid was comparatively investigated. Also，the flat-rheology mechanism of water-based drilling fluid was explored，in combination with the molecular aggregation structure of rheological modifier. The results showed that the average molecular weight of rheological modifier was 7.5×10⁶，the average particle size was 258.7 nm，and the temperature resistance was high up to 260℃ . In water-based drilling fluid，the rheological modifier adjusted the rheological property well，which could dramatically reduce the influence of temperature variation （4—65℃） on rheological parameters. It was concluded that the core-shell structure of rheological modifier should reinforce molecular rigidity and stability. In particular，a layer distribution of hydrophilic radicals around the shell could compensate radical loss caused by harsh environment，and sustain the total quantity of effective radicals. As a result，the association action between polymeric molecular and clay layers could be well maintained，and the flat-rheology of water-based drilling fluid could be realized.

Abstract:In order to improve the thermal resistance of the coating agent for water based drilling fluids，the amphoteric polymer as a high temperature resistant coating agent（PAAND）was synthesized through radical copolymerization using acrylamide（AM）、N-vinylpyrrolidone（NVP）and diallyldimethylammonium chloride（DMDAAC）as main raw materials. The optimum synthesis conditions were as follows：monomer mass ratio of AM to NVP to DMDAAC was 1∶6∶3，dosage of initiator was 0.1%，reaction temperature was 55℃，reaction time was 5 h and hydrolysis degree of AM was 60%. The structure and properties of the polymer were analyzed by infrared spectra analysis，thermogravimetric analysis and scanning electron microscopy，the coating properties were evaluated. The results showed that the decomposition temperature of PAAND was 232℃，and the coating properties of the PAAND at high temperature were excellent，the hot-rolling recovery rate and the second rolling recovery rate after 16 h at 180℃ being of 80.85% and 79.16% respectively，and the dynamic shear rate being as low as 164%. In a word，the coating properties of the PAAND at high temperature were better than that of KPAM and FA367 commonly used. The PAAND was coated on the surface of the cuttings by multi-point adsorption，forming a polymer "protective film" to prevent the direct contact between the cuttings and moisture.

Abstract:Aimed at the problem of sluice instability in silt formation in oil and gas well drilling，based on the technical requirements of drilling fluid and the optimization of molecular structure，a type of environmental protection polyamine strong inhibitor HGI was developed using triethanolamine，maleic anhydride and glacial acetic acid as raw materials. The inhibition performance of HGI was discussed by using the new evaluation method （X-ray diffraction analysis，thermogravimetric analysis） and the traditional evaluation method（particle size distribution experiment，rheological experiment），in addition，the inhibition mechanism of HGI was analyzed. The results showed that the HGI could effectively inhibit the hydration and dispersion of shale，showing more prominent inhibitory performance than that of the similar polyamine inhibitor UHIB-Ⅰ and UHIB-Ⅱ.The HGImolecules was intercalated into the interlayer space of the clay by electrostatic interaction and hydrogen-bond interaction between HGI molecules and the surface of clay crystal layer. In addition，the hydroxyl groups in the HGI molecules formed a chelating bond with the metal ions on the surface of the clay crystal layer with their unique "claw" structure，which was tightly wrapped on the surface of the clay crystal layer and played a certain role. The new characterization system of measurement of crystal interlayer spacing by X-ray diffraction analysis，could make up the deficiency of the traditional method of linear expansion of normal temperature and normal pressure

Abstract:Compared with conventional well，deepwater and ultra-deepwater well had narrower safety density window of drilling fluid，which gave stringent technical requirements for drilling fluids. Aiming at this problem，the effects of low density agent LDA60 and water-soluble pressure plugging agent PF-STRH on the density，rheology and pressure bearing of drilling fluid were studied，the advantage and disadvantage of full-hydrate scheme and half-hydrate scheme inhibition were compared. Finally，PF-STRH and hydrate control technology were applied on deepwater well LS25-1-S1 with high temperature and pressure and ultra-deep well LS18-1-1 in South China Sea. The results showed that LDA60 could effectively reduce the density and had little effect on the rheology of drilling fluid. The pressure bearing capacity of HEM drilling fluid could be improved by 2 times after adding 3% PF-STRH，indicating good effect. Half-hydrate scheme was recommended during deepwater drilling operation considering the cost and environment. After pressure plugging and hydrate inhibition operation，the density of drilling fluid reduced and pressure bearing improved with no influence on rheology. PF-STRH and hydrate control technology could be used in the drilling of deep water and ultra-deep water wells with narrow density window.

Abstract:In order to obtain fracturing fluid with excellent temperature resistance，tetra-polymer thickener MASD for fracturing fluid was prepared using acrylamide（AM）and acrylic acid（AA）as backbone monomers and 2-acrylamide-2-methyl propane sulfonic acid（AMPS）and β-cyclodextrins（β-CD）as functional monomers. The structure of MASD was characterized with FTIR spectrum and 1H-NMR spectrum，and the major performance of MASD was evaluated. Furthermore，the temperature and shearing resistance，core damage property of the fracturing fluid，which was composed of MASD and organic zirconium crosslinking agent，were studied. The results showed that MASD had stable chemical structure at 250℃ ，good rheological property and strong thickening ability，which synthesized on the condition of 23% total concentration of monomers，7∶1∶1∶1 mass ratio of AM∶AA∶AMPS∶β-CD，0.3% initiator dosage in terms of monomers mass，7 pH value，initiating at 40℃ for 0.5 h and then continuing at 60℃ for 8 hrs. The viscosity of 0.6% MASD solution was 72 mPa·s at room temperature. The rate of sand sedimentation was 1.78×10^-4m/min，indicating good sand carrying capacity of MASD solution. The fracturing fluid containing 0.6% MASD and 0.5% organic zirconium crosslinking agent had good temperature and shearing resistance. The final viscosity of fracturing fluid system was about 170 mPa·s after continuously shearing for 90 min at 120℃ or 140℃ and 170 s^-1. The core damage rate of fracturing fluid was low to 14.27%. The thickener MASD could be used for medium-high temperature fracturing construction.

Abstract:In order to further improve the temperature and shear resistance of cationic polymer fracturing fluid，a kind of fracturing fluid which used cationic polymer PAAD as thickening agent and the compound of resorcinol（FA），hexamethylenetetramine（FB）and organic titanium TCMH as cross-linker was prepared. The effect of compound cross linker on the performance of temperature and shear resistance was investigated. The results showed that the cross linking reaction occurred between thickening agent PAAD and the compound of FA and FB at high temperature，which improved the stability of cross-linking structure. The performance of cationic polymer fracturing fluid was related to the mass ratio and concentration of FA and FB. The fracturing fluid had a quite good performance on temperature and shear resistance when the mass ratio of FA and FB was 1∶2 and the dosage of FA and FB was 0.15%—0.3%. The PADD fracturing fluid which cross-linked by TCMH-FA-FB had better performance on temperature and shear resistance compared with that of PAAD fracturing fluid which cross-linked by TCMH without FA-FB. The viscosity of PADD fracturing fluid（pH=3—4）that contained 0.6% PAAD，1.0% TCMH and 0.3% FA-FB（FA∶FB=1∶2）remained 60 mPa·s after continuous shearing for 90 minutes at 160℃ and 170 s^-1，which could meet the requirement of fracturing construction in oil and gas wells at 160℃.

Abstract:In order to improve the basic performance of xanthan gum and widen its application，hydrophobic cationic etherifying agent （3-chloro-2-hydroxypropylhexadecyldimethylammonium acetate） was prepared by epichlorohydrin and hexadecyldimethylamine，and then a novel hydrophobic amphoteric xanthan gum was synthesized by xanthan gum（XG）and the etherifying agent. The rheological properties，proppant carrying capacity，drag reduction and heat and shear resistance of HAXG solution were studied in detail. The rheological results showed that the apparent viscosity of HAXG solution was significantly enhanced. The apparent viscosity of 0.4% HAXG solution（172.38 mPa·s）was 4.05 times as big as that of 0.4% XG solution（42.54 mPa·s）. Both XG and HAXG solutions behaved as pseudoplastic shear-thinning fluids，and the shear thinning behavior could be fitted quite well with Cross model. Compared with XG solution，HAXG solution exhibited more obvious thixotropy，much stronger viscoelasticity and network structure，thus better proppant carrying capacity and better heat and shear resistance. Both the two solution exhibited good drag reduction performance. With the concentration of 0.12%，the largest drag reduction rate of XG and HAXG solution was 57.80% and 65.01% respectively，indicating HAXG solution exhibited better drag reduction than XG solution. HAXG could be used as a drag reducing agent for slickwater fracturing fluid.

Abstract:In order to improve the in-depth profile control action of particulated plugging agent，the particle size，microstructure，suspension performance，plugging rate and blocking mechanism of the micro-scale self-assembled particles（MSSAP）with double layer coating，were studied by laboratory experiments. The results showed that the size of the prepared spherical self-assembled particles were 56.5—270.5 μm，and it had a good suspension performance in the polymer solution，suspension rate reaching 90% in a 0.3% polymer solution for 20 h. Block experiment showed that its plugging rate was above 90% after injection of self-assembled particles system（5% MSSAP + 0.2% polymer）at 65℃ into the cores with permeability of 9000 × 10^-3—15000 × 10^-3 μm². The distribution state of MSSAP particles in the core after sealing showed that the plugging mechanism of the MSSAP were plugging，adhesive bridge blocking and adhesive filling.

Abstract:In order to obtain oil displacement system suitable for high temperature and low permeability reservoir，a double dispersion system was prepared blending polyacrylamide microsphere（TS-1）which matched formation hole roar diameter and polymer KYPAM-10. The suspension of TS-1 and thermal stability，plugging and profile performance of double dispersion system were studied. The results showed that TS-1 had good suspension behavior in double dispersion system. Polymer and TS-1 had good compatibility. The viscosity retention rate of double dispersion system was more than 80% after ageing 180 days in 95℃ oven. With increasing aging time，the particle size of microsphere increased slightly. The injection and migration of double dispersion system were good，whose sealing rate and residual resistance coefficient in the core were greater than that of single microsphere system. The separation rate of low permeability core increased from 20% to 60% after 0.5 PV double dispersion system composed of 1500 mg/L KYPAM-10 and 500 mg/L TS-1 was injected to double-pipe parallel cores，which effectively improved water absorbing capacity of low permeability core. It effectively improves the water absorption capacity of low permeability core. The oil recovery rate of double dispersion system increased by 24.15% on the basis of water flooding，and that was 5.78% higher than that of single polymer flooding，showing good oil displacement effect. The double dispersion system could be used for reservoir flooding and profile control at 95℃ in Shuanghe oilfield.

Abstract:There was still a gap between actual oil increase effect and expected value of chemical flooding. One of the main reasons was that the compatibility between profile control agent and pore size of reservoir rock was poor，and the effective retention and displacement could not form，which restricted the exertion of profile control and oil displacement technology. In order to improve the effective retention of flooding agent in pore throat and achieve the effect of liquid flow steering，the seepage characteristic and mechanism of polymer solution，gel and microsphere were studied based on reservoir and fluid properties of Bohai oilfield. The results showed that the resistance coefficient and residual resistance coefficient of Cr³⁺ polymer gel were larger than those of polymer solution，and the residual resistance coefficient was greater than resistance coefficient，showing unique seepage characteristic. Polymer microsphere had the characteristic of slow expansion，and could enter into the core pore before water swelling and expand in it，which resulted in strong retention and sealing and better effect of fluid diversion. Compared with molecular aggregate in polymer solution，the particle size distribution of polymer microspheres was more concentrated. In the same core condition，the volume inaccessible of polymer microspheres was larger，but the remaining oil in inaccessible pore volume could be affected by carrying fluid of microsphere，which improved the overall sweep efficiency.

Abstract:In order to improve the shortcomings of traditional plugging particles，the performance of temperature resistance and salt tolerance，sealing characteristics and plugging mechanism of a new type bridging particles consisted of rigid kernel and softening film were studied. The results showed that the average diameter of bridging particle was 117.23 μm. The bridging particle had good temperature resistance and salt tolerance，which could adhere stably at 150℃ and 35 g/L salinity. The plugging effect of bridging particle was good on the optimum plugging condition of 1.0 mL/min injection rate，0.05 PV slug size，5.0% particle dosage and 0.2% guar gum suspending agent dosage. After plugging on optimum condition，the water flooding pressure gradient of high permeability sand pipe rose from about 3 to 41.82—141.70 kPa/m，the permeability decreased from 9—12 μm² to about 0.24 μm²，and the effective plugging rate was above 97% . Microscopic visual model research revealed that bridging particle displacement system had plugging function with filling，bridging and adhesion. When the diameter of bridging particle was larger than that of pore throat，it displayed filling function during plugging，when that was 1/3—2/3 of pore throat diameter，it displayed bridging and adhesion function. The bridging particles could be used to block high permeability channel path in middle and late development stages of water flooding oilfield.

Abstract:Based on the critical problems of low efficient or invalid circulation during waterflooding development in low permeability and fractured oilfield，this paper introduced a long term intelligent in-depth profile control slug combination technology，which used flexible particles as main slug，soft micro gel ball and swellable particles as preset slug and protective slug.The characteristic of flexible particle was studied，and the field applications of flexible particle single slug and combination slug were compared. The experiment results showed that the flexible particle had excellent temperature resistance，salinity tolerance，stretching resistance and resilience. The flexible particle had plug，deformation and secondary bonding capacity in reservoir，which was efficient to fill and plug fracture and realized the purpose of intelligent，dynamically on-way and in-depth profile control and dynamical expansion of sweep volume. The field application results showed that in-depth flow diversion and dynamical profile control could be realized by flexible particle single slug，which was good for increasing oil production and decreasing water cut. The combination slug which consisted of flexible particle，soft micro gel ball and swellable particles could reach even beyond the flexible particle single slug on the effect of increasing oil production and decreasing water cut，and significantly reduce the amount of flexible particle and save cost.

Abstract:In order to solve the negative influence of the high salinity of formation water on the performance of the deep liquid flow divertring agent in the CaCl₂ water type oilfield，reduce the cost of the steering agent，and then achieve the purpose of reducing the cost and increasing the efficiency，the gel performance，plugging and diverting performance and field application of a composite silicate microgel diverting agent OMGL，synthesized by a variety of inorganic materials through special processes，in the CaCl₂ water type formation water was discussed. The diverting agent OMGL reacted with Ca²⁺ and Mg²⁺ in high salinity formation water（injected water）. The gelation reaction of 0.6%OMGL in oil field water completed within 12—24 h at room temperature. With the increase of OMGL concentration，the gelation degree of the system increased and the gelation degree of the 3%OMGL+1%CaCl₂ aqueous solution system was 100%. The microgel with particle size of 0.05—2 μm was formed by the gel reaction of OMGL with Ca²⁺ and Mg²⁺ in the formation water，which was difficult to enter the low permeability microporous matrix，and a stable microgel coating was formed through the —Si—O—Si— bond on the surface of the rock skeleton of the dominant channel. The diverting agent OMGL was ideal for plugging the core with a permeability ratio of 10数 50 times. This kind of diverting agent had been carried out in the field experiments with different temperatures and different salinity conditions at home and abroad，the effect of the enhancement of oil recovery of water flooding was good，the water injection pressure increasing by 2—3 MPa，and the oil increasing effect being good and the effective period being over 1 years.

Abstract:In order to control the blockage of deep wells in Yingxi area，Qaidam Basin，reservoir rock characteristics and precipitate composition were studied by scanning electron microscope and ion titration technology. The blocking mechanism was also analyzed.The prevention technology was used to carry out field operation in seriously blocked well，which was injected deposition inhibiting composition through annularspace. The results showed that there were NaCl crystal particles in the pore，rock surfaces and fracture of reservoir. The blockage was mainly NaCl with cubic crystal structure. In well hole and swabbing process，NaCl crystal particles formed under the condition of changing reservoir thermodynamics，crystallization kinetics and hydrodynamic. Moreover，plugging in oil wells would be caused by crystallization deposition，as the enrichment of inorganic matter and a few organic impurities enhanced. The sediment inhibition rate of blockage was 90.0%—94.3% after prevention technology which was injected deposition inhibiting composition through annularspace. The load and shape of indicator diagram became smoother after treatment. The well washing cycle was extended for 44 days and the production stability of oil well was improved.

Abstract:The ultra-low permeability reservoirs in Ordos Basin face serious problems of water injection difficulty，poor flooding results and low oil recovery. In order to improve the oil recovery of ultra-low permeability reservoir，the development idea of CO₂ huff-n-puff was proposed based on the characteristics of ultra-low permeability reservoirs and the successful cases of CO₂ flooding in abroad. Long core flooding experiment were done in laboratory，and the effect of CO₂ huff-n-puff were evaluated combining the oil change rate and displacement efficiency，meanwhile，the injection parameters were optimized. The experiment result showed that CO₂ huff-n-puff had higher oil recovery when reservoirs pressure was greater than the minimum miscible pressure（MMP），being of 20.78 MPa. The optimum operation strategy was 0.1 PV for slug size，the soaking time of 24 h and three-cycle huff-n-puff. CO₂ huff-n-puff provided an effective method for ultra-low permeability reservoir，the oil displacement efficiency was 56.39% ，the average oil exchange ratio was 0.454.

Abstract:Whether CO₂ flooding can be mixed with crude oil under reservoir conditions directly affects the oil displacement efficiency，therefore CO₂ miscible and near-miscible flooding in low permeability reservoirs was studied. By conducting CO₂ flooding experiment in both homogeneous and heterogeneous rectangular cores，the oil recovery results were acquired through the various series of experiments considering permeability，migration distance，permeability differential as well as the flooding pressure under the simulated reservoir conditions. Therefore，the classification of the immiscible，near-miscible and miscible CO₂ flooding in low permeability reservoir was determined by the gas flooding results，and the near-miscible area was also defined. The minimum miscible pressure（MMP）of CO₂ with crude oil was 18.5 MPa in this study，which was 0.7 MPa higher than that determined by slim tube experiment（17.8 MPa），a conventional method to determine the carbon dioxide MMP. Based on the displacement curve，the CO₂ flooding process was divided into three stages，immiscible，near-miscible and miscible region. The near-miscible pressure of CO₂ displacement in YC oil ranges from 16.5 MPa to 18.5 MPa. The MMP measuring of CO₂ flooding was determined by core flooding method and the near-miscible flooding region was defined，which offered reference to the further understanding of mechanism in CO₂ near-miscible displacement and scheme design of CO₂ flooding in YC oilfield.

Abstract:The difference of physical properties between heterogeneous reservoirs is an important factor affecting the recovery of polymer flooding. Focusing on the varying pattern of liquid productivity index in the process of water flooding to polymer flooding，the variation of liquid productivity index in different permeability ratio were studied with physical simulation experiment. The experimental results showed that there were four phases for the liquid productivity index in the process of water flooding to polymer flooding：water flooding increasing phase，polymer flooding rapid decreasing phase，polymer flooding gradually decreasing phase and polymer flooding increasing phase. In the heterogeneous core flooding experiment，the change of reservoir permeability ratio difference had obvious effect on the decrease of the liquid production index in the polymer flooding stage，the liquid production index，oil recovery decreased with the increase of the permeability ratio. The experimental results could afford a guide for the reasonable estimation of polymer flooding liquid production decreasing range and the forecasting of polymer flooding liquid production decreasing period.

Abstract:In order to further reveal the microscopic rule and mechanism of polymer flooding， according to the pore structure， the idealized microscopic displacement visual model was designed， and then the effects of displacement speed， polymer viscosity， pore structure and oil viscosity on the displacement efficiency of cluster-residual oil was systematically studied. The results showed that the increasing velocity led to the increase of the displacement pressure， which was the main reason for the increase of displacement efficiency. When the viscosity of the displacement system was the same， the greater the elasticity was， the easier it was to displace the residual oil. When the variable diameters ratio was higher than critical value， and the small pore width was fixed， the cluster residual oil was difficult to be displaced；on the contrary， when the variable diameters ratio was the same， and the small channel width was lower than critical value， the oil displacement efficiency was almost zero. With the increase of the oil viscosity， the displacement efficiency of cluster-residual rapidly reduced. It was concluded that the influence of concerned factors on the oil recovery in a decreasing order including oil viscosity， the first normal stress difference， displacement velocity.

Abstract:In order to obtain hydrophobically associating polymer with good temperature resistance， an hydrophobically associating amphiphilic polymer AHAPAM was synthesized by using acrylamide（AM）， sodium p-styrenesulfonate（SSS）， N， N-dimethyl octadecyl allyl ammonium chloride（DMAAC-18） . The preparation condition of AHAPAM was optimized by measuring the viscosity of AHAPAM solution， and the temperature resistance and salt tolerance of AHAPAM were studied. The results showed that the critical associative concentration of AHAPAM was 0.19% under optimum synthesis condition with 1.5% mole fraction of DMAAC-18， 0.6% mole fraction of SSS， 25% monomer mass fraction， 0.2% initiator（a combination of（NH₄） ₂S₂O₈ and NaHSO₃ in mole ratio 1.2∶1）， 45℃ reaction temperature， 9 pH value， and 6 h reaction time. When the concentration of AHAPAM was higher than the critical associative concentration，the intermolecular association between hydrophobic chains of AHAPAM was predominant and a spatial network structure was formed. The viscosity of 0.5% AHAPAM solution was about 90 mPa·s at 120°C and 170 s^-1 shearing for 1.4 h， showing good temperature resistance. The viscosity of AHAPAM solution was about 330 mPa·s when the dosage of sodium chloride and calcium chloride was 18% and 15% respectively， indicating good salt tolerance.

Abstract:Due to high hydrophobic-monomers content， strong hydrophobicity and association， the traditional low-molecular-weight hydrophobic association polymers usually had some problems during flooding， such as large adsorption and retention and poor injectivity. The flow and displacement characteristics of an associated polymer（AP-P5）which had low hydrophobic-monomers content and ultra-high-molecular weight were investigated. Moreover，these properties were compared with those of strong-hydrophobic polymer（HAPAM）and partially hydrolyzed polyacrylamide（HPAM） . The results showed that， due to the weakened hydrophobicity， the apparent viscosity， injection pressure， resistance factor（Fr）， residual resistance factor（Frr）and dynamic retention of AP-P5 were all much lower than those of HAPAM but still higher than those of HPAM. In the heterogeneous model with a permeability ratio of 10.0， HAPAM and AP-P5 could both enter high and low permeable layers while HPAM mainly existed in high permeable layer， indicating that HAPAM and AP-P5 had stronger profile control capability than HPAM. For the weakened hydrophobicity， reduced dynamic retention and increased migration capacity， the persistence and effectiveness of AP-P5 flooding were improved. As a result， the enhanced oil displacement efficiency of AP-P5 was higher than that of HAPAM， but still lower than that of HPAM in homogeneous models. So it could be concluded that the hydrophobicity of polymers should be further reduced from the perspective of enhancing displacement efficiency. In heterogenous models， AP-P5 could both improve the injection profile and reduce adsorption and retention of polymers. Consequently， the enhanced oil recovery rate of AP-P5 was higher than that of HAPAM and HPAM.

Abstract:Aiming at lower oil recovery increment of some clean fracturing flow-back fluid used in simple system， a method using the synergistic interaction between anionic and cationic surfactants was established to realize the reutilization of clean fracturing flow-back fluid in surfactant flooding， based on fundamental performance evaluation of flow-back fluid. The interfacial tension behavior， emulsification ability， adsorption behavior and enhanced oil recovery efficiency were studied systematically in laboratory. The results showed that the effective recipe of oil-displacing compound system was 0.2% RSH-2 + 0.012% AOS. The oi/water interfacial tension could only be lowered to 10^-1 mN/m with single flow-back fluid， but could be further lowered to 10^-3 mN/m through adding AOS with concentration 0.012%. The system had excellent emulsification performance， the water separation rate of the emulsion with oil-water ratio of 1∶1 was only 30% after 10 hours. Meanwhile， the dynamic retention amount was about one fourth to one third of the dynamic adsorption（about 7.52 mg/g） . The physical model experiments indicated that the oil recovery value could be enhanced 11.8% under optimal injection project， which confirmed its excellent performances on further enhanced oil recovery for low-permeability reservoirs after fracturing treatment.

Abstract:The crude oil reserves of tight reservoir in peripheral area of Daqing are very rich. However， the development degree of reserve is low due to the lack of effective technologies. The imbibition recovery is one of the important technical measures which are used to develop efficiently the hydrophilic tight reservoir. In order to devlop the efficence exploitation technology of the weak oil-wet tight reservoir，the imbibition recovery effects of anionic/nonionic surfactants“HLX”，“SYH（petroleum sulfonate）+ Na₂ CO₃ ”，cationic surfactants“YANG”and nonionic surfactants“DCY”on the weakly hydrophilic cores with the permeability of about 2×10^-3μm² were investigated. The results showed that the recovery efficiency and imbibiton rate of imbibition system were influenced not only by oil-water interfacial tension but also by the wettability of the rock porous surface. The results of the physical simulation experiment of imbibition recovery showed that” YANG”and ” DCY”imbibition system could not only change the wettability of rock pore surface but also reduce oil-water interfacial tension， hence， their ability to enchance the effect of imbibition recovery was better and the enhancement of oil recovery was greater. However， as a cationic surfactant， "YANG" had a larger adsorption capacity in reservoir rock pore， which would lead to a lower enhancement of imbibition oil recovery. As a result， It was recommended to use a "DCY" imbibition system with mass fraction of 0.3%.

Abstract:The emulsification of the produced water after the binary compound flooding in the extra high salinity reservoir with the salinity of 30×10⁴ mg/L is serious and the demulsification treatment is difficult. A type of salt-tolerant polymer demulsifier， which was different from the conventional polyether or the modified polyether， was synthesized in this paper through copolymerization among the main monomer AM，salt-tolerant association monomer AMPS and sodium styrene sulfonate using the potassium persulfate-sodium bisulfite initiator， and the optimal synthesis conditions was determined by orthogonal experiment. The results showed that when the molar ratio of AM to AMPS was 2 ∶1；the mass ratios of the SSS and the initiator to the total monomers was 4% and 1.5% ， respectively；the reaction temperature was 80℃ ；the reaction time was 6 hours and the pH was 9， the obtained demulsifier， named as HYDR2， had good demulsification effect. The demulsification effect of HYDR2 was better than that of the demulsifier AE1910 used in the field. When the concentration was 5 mg/L， the dewatering rate of HRDR2 and AE1910 to the produced fluid after 10 hours was 99.5% and 89.6%， respectively

Abstract:In order to improve water flooding efficiency of zone Ⅳ5-11， a mature field with high temperature of 81.0℃， high water cut of 97.9% and high recovery factor of 53.3%， the adaptability of weak base（Na₂CO₃）ASP displacement system for high temperature reservoir was studied. The experimental results and field application results showed that the long term thermal stability of weak base ASP flooding formula was good， after ageing 180 days at 81℃， the interfacial tension（IFT）between the system and the crude oil maintained about 10^-4 mN/m magnitude， and viscosity retention ratio was 147.6%. The damage of the system to the formation is not obvious with weak dissolution and low alkali consumption under Ⅳ5-11 reservoir conditions. The Na2CO3 played a great role in the whole process from the injecting well to the produced well. The weak base ASP flooding technology had been used in Ⅳ5-11 block successfully， the oil production of center produced well increased from 23.0 t/d to 106.1 t/d， water cut reduced from 97.9% to 90.2％， the oil recovery had been enhanced by 9.1% OOPI， the predicted oil recovery would be increased by 14.2% OOPI

Abstract:To investigate the emulsifying property of ASP system without ultra-low interfacial tension（IFT）and its effect on EOR， the emulsifying property of 5 different surfactants were calculated by using an emulsifying property index I_e ， and an ASP system formula with good performance in emulsifying and non-ultra-low interfacial tension was screened out；the radial fluid flow flooding experiments were also conducted to investigate the oil displacement effect of the ASP system. The results showed that the Ie of the surfactants from strong to weak were OP-10， HABS（sodium alkylbenzene sulfonate）， BS-12（lauryl betaine）， AES（sodium alcohol ether sulphate）and OP-4 in the same conditions， and when the alkali mass fraction was 0.3% ， the ASP system had the best emulsifying property. The optimum formula of the ASP system with non-ultra-low interfacial tension was as follows， NaOH mass fraction was 0.3%， the surfactant（60%OP-10+40%HABS）mass fraction was 0.3%， and the polymer（relative molecular weight 2000 ×10⁴）mass concentration was 1500 mg/L. The viscosity of the system was 42.9 mPa s（45℃， 6 r/min）， and the interfacial tension between the ASP system and oil was 0.0415 mN/m， and the Ie was 0.688. The optimized ASP system could not only expand the swept volume， but asso improve the oil displacement efficiency during flooding process， and its effect on enhanced oil recovery was no less than that of the traditional ASP system with ultra-low-IFT.

Abstract:An economic chemical method was proposed based on the reaction between alkali and high acid crude oil， and the physical properties of the formed emulsion， flow behaviors and oil displacement efficiency were comprehensively investigated. It was shown that under the condition of oil to water ratio of 0.5 ∶9.5， an unstable and three stable O/W emulsions were prepared by adjusting the rotating speed（1500—2600 r/min）and stirring time（0.5—2 h） . Due to the Jiamin effect， the injection pressure of the stable emulsion significantly increased when flowing in the core， while the unstable emulsion occurred oil-water separation， and the injection pressure did not change significantly. The stable emulsion formed at a rotational speed of 2000 r/min and a stirring time of 1.5 h could effectively increase oil recovery by up to 17%. When the matching factor f between the emulsion droplets and the rock pore throats was less than 1， the oil displacement efficiency of the emulsion was not high；when f was greater than 1， the emulsion droplets can effectively block the pore throat and increase the recovery efficiency. However， the higher f was not always better.

Abstract:In order to solve the problem of dehydration of aging oil in liaohe oilfield，p-tert-Butylphenol formaldehyde resin demulsifier was synthesized through ethylene oxide （EO） and propylene oxide （PO） polymerization reaction using p-tert-butylphenol formaldehyde resin as the initiator in the presence of KOH catalyst. The effect of the different proportion of initiator to PO， EO to PO on the performance of the dehydration， and the hydroxyl value， cloud point， HLB value and water number of demulsifiers was probed. The experimental results showed that when the ratio of initiator and PO was 1∶149 and the ratio of EO to PO was 1∶2 ， the obtained demulsifier PTAE7 had the best demulsification effect. The cloud point， water number and HLB value of the demulsifier was affected by initiator/PO and EO/PO ratio. The cloud point of the demulsifier PTAE7 was 27.8℃， the water number was 7.34 and the HLB value was 6.62. After being treated by demulsifier PTAE7 with dosage of 100 mg/L for 150 min at the temperature of 85℃， the dehydration rate of the crude oil was up to 95.28% ， and two-phase separation was visible with clear interface

Abstract:In order to study the deposition behavior of barium sulfate scale in pipelines of oilfield water injection system，the deposition process of barium sulfate in microchannel pipelines was measured and analyzed by differential pressure method and flame atomic absorption spectrophotometry， and a related depositional dynamics model was established. The influence of different factors on the reaction kinetic coefficient（ka）and the pipeline deposition coefficient（β）was investigated. The results showed that ka and β gradually increased with the reaction. It indicated that ka increased with increasing pipeline，flow rate，and initial concentration of BaCl₂ and Na₂SO₄. β had a nonlinear increase with increasing pipeline and flow rate， and had a linear increase with increasing concentration. With the increase of temperature， the increment of β increased. While ka did not change significantly in the early stage of the reaction and increased in the later period of the reaction. Equations of ka and β were obtained by fitting the experimental data，and the corresponding calculated values were roughly in accordance with experimental measurements. The concentration of barium at the exit of pipeline calculated from established simplified model was basically consistent with experimental measurements，which illustrated that it was reasonable to explain the deposition kinetics model of barium sulfate reaction system based on assumptions.

Abstract:In order to effectively prevent the plugging of pipeline and equipment caused by barium sulfate scaling in the process of oilfield exploitation， and overcome the shortcomings of physical anti-scaling methods such as ultrasonic wave， magnetic field， and high-frequency electric field. According to the shallow pool theory， a physical fixed point descaling device containing mixing zone， scaling area and buffer zone was developed. The descaler frame was a cube， the scale plate was flat， and the clamping plate had threeangles of 45°， 60°， and 90°. Inductively coupled plasma emission spectrometer（ICP）was used to detect ion concentration at the outlet of descaling device，avoiding human errors. The influence of reaction time，initial concentration of fouling ion and temperature on the scaling rate of barium sulfate was studied by the descaling device. The results showed that the descaling effect of fixed-point descaling device was good and the scaling rate was about 99.9%. Reaction time， initial concentration of Ba²⁺ and SO₄^2- had little effect on the scaling rate of barium sulfate. 5—10 min was the best scaling time for barium sulfate in the fixed-point descaling device. The scaling rate of barium sulfate increased first and then decreased slightly with increasing temperature. The best scaling temperature was 50℃. When the mass concentration of Ba²⁺ was 742 mg/L and the molar ratio of Ba²⁺ to SO₄^2- was 1∶4， the scaling rate of barium sulfate could reach 99.99%

Abstract:In order to study the effect of oilfield produced water and pipeline material on the corrosion of oil-water mixed transportation pipelines in oilfield ground， the correlation between S^2- content， pH value and salinity of sewage， pipeline material and the corrosion rate of steel was analyzed by measuring the corrosion rate of carbon steel produced by different standards and stainless steel in produced water of 33 blocks， and combining with the statistical analysis software SPSS. The results showed that the chemical composition of carbon steels was similar. The correlation coefficient of corrosion rates between carbon steel materials was greater than 0.945， showing a significant positive correlation. The corrosion resistance differences of several kinds of carbon steel in oilfield produced water were small. Because of the alloy elements Cr and Ni， the corrosion resistance of stainless steel material was greatly enhanced. The content of S^2- in oilfield produced water had a great influence on the corrosion of carbon steel. With the increase of S^2- concentration in oilfield produced water， the corrosion rate of carbon steel increased first and then decreased. When the dosage of S^2- was 68 mg/L， the carbon steel had the maximum corrosion rate（0.1823 mm/a） . When the dosage of S^2- in sewage was less than 70 mg/L， S^2- had a significant positive correlation with corrosion rate of carbon steel which correlation coefficient was 0.523 and the probability（P）was 0.003. The pH value and salinity of sewage had a little influence on the corrosion of carbon steel.The correlation index between pH value and salinity of sewage and corrosion rate of carbon steel was 0.238 and 0.130， and the probability（P）was 0.182 and 0.468 respectively， showing a limited correlation to corrosion

Abstract:In order to resolve high viscosity-loss-rate problems in preparing the polymer solution using the produced wastewater of polymer flooding， the main factors affecting polymer solution viscosity were investigated and polysilicon aluminum flocculant were synthesized. Besides，flocculant purification performance and viscosity stability were evaluated，scaling trend of purified water under stratigraphic conditions was simulated by Oil Scalechem prediction software， and the particle size of the polymer system was analyzed by laser granulometry. The results indicated that the effect of Fe²⁺， Ca²⁺， Mg²⁺， S^2- and suspended solids content in solution on the viscosity of the polymer solution was greater than that of the others， hence， it must be controlled in preparing polymer solution. The optimal dosing formula of the flocculant with the performance of removal of turbidity and calcium was as follows， 50mg/L PFS + 200 mg/L PSiAS-1 + 8 mg/L setting agent. The content of Ca²⁺， Mg²⁺ and residual polymer of the purified water，obtained by deepened processing with the flocculant， decreased sharply， and the oil content and suspended solid content was lower，moreover， the purified water hardly contained Fe2+. The average particle size of suspended particles（SS）in purified water was lessthan 100 nm， which was smaller than the pore diameter or the cores， so formation could not be blocked by SS. As a result， the purfied water could be reused for preparing the polymer flooding solution.

Abstract:The produced water of SHM gas field was characterized by high oil content， high suspended solid content， high salinity， weak acid and slow separation of oil and water， which affected the normal operation of re-injection system. The produced water was treated by coagulating sedimentation， and the types and dosages of pH regulator， iron removal agent， inorganic flocculant and organic flocculant were studied. Finally， the effect of dosing interval and dosing order on flocculation was researched. The results showed that the water quality changed from weak acid to neutral after the following steps. First， 0.5 ml/L of iron removal agent hydrogen peroxide solution was added to the wastewater. Second， the pH value was adjusted to about 7.5 with NaOH 3 minutes later. Third， 100 mg/L inorganic flocculant PAC was added 1 minute later， and 6 mg/L organic flocculant cationic polyacrylamide was added 2 minutes later. After the treatments， the complete flocculation time of floc was 8 min， and the suspended solid content decreased from 400—700 to 14—30 mg/L， the oil content decreased from 722—1366 to 32—42 mg/L， which met the quality requirement of injection water.

Abstract:Water plugging and profile control agent played a crucial role on improving the effect of waterflooding development and enhancing oil recovery in high water-cut oilfield. The advantages and disadvantages and application status of traditional water shutoff agents like weak gel and granule materials were reviewed. The characteristic of plant oil and its research progress， application and existent problem in new fields such as plant oil based polysulfide rubber and ecological lubrication materials were introduced. The applications of plant oil and industrial by-product oil foot on water shutoff in oilfield through chemical modifications such as vulcanization， esterification and saponification hydrolysis were proposed. Plant oil and oil foot had broad application prospect on the field of deep water plugging and profile control due to low price， easy chemical modification and good sealing effect on cores

Abstract:Relative permeability modifiers（RPMs）could greatly reduce water phase permeability and had little effect on oil phase permeability in reservoir which could achieve water control and enhance oil production. The traditional RPMs system was generally water-soluble polymer with high molecular mass or weak gel system， which mainly used to block oil and gas reservoirs with high permeability， large pores and fractures. Nano-SiO₂ RPMs systems had the advantages of surface effect， volume effect， quantum size effect and so on. They could enter micron and nanometer pore throats which led to the formation of nano-film and achieved effective development of low and ultra-low permeability oil and gas reservoirs. The worldwide research status and mechanism of RPMs system were introduced in this paper. The composition and effect of nano-SiO₂ which used in the improvement of oil and water phase permeability were summarized，along with its function mechanism. Finally the problems and development trends in the process of preparation， evaluation， mechanism analysis and application promotion of nano-phase RPMs were pointed out.