The supporting technologies of chemical flooding such as reservoir engineering, flooding agent and surface engineering have been formed in Henan Oilfield. The industrial application has been carried out in 26 units and which include Class I and II reservoirs and develop towards Class Ⅲ reservoirs by chemical flooding. It experiences the application of polymer flooding, compound flooding and heterogeneous flooding, which becomes the main technologies for stabilizing production or delaying production decline. With the comprehensive utilization of high-quality resources, it is faced with the challenges of lack of high-quality chemical flooding resources, the decline of chemical flooding project benefits, and the development and innovation of chemical flooding technology. Therefore, the countermeasures are to ensure the foundation, adjust the technology route, strengthen the technical research, deepen the injection-production process support, research and develop the matching skid-mounted surface polymer injection system, optimize the oil displacement agent with high cost performance, reduce the investment, promote the efficiency of chemical flooding, and improve the utilization rate of chemical flooding reserves, so as to achieve the orderly connection of chemical flooding reserves

With the increasing oil demand in China, it is very important to further tap the potential of oil and gas fields. Chemical flooding technology is one of the important technologies of EOR, and polymer flooding, as the most important method of EOR, has been widely used in the field and achieved good oil displacement effects. Therefore, by summarizing the basic principles of polymer flooding, the development status of various kinds of polymer for oil displacement and the field application effect of polymer flooding, the development direction of polymer flooding in harsh reservoir conditions, such as high temperature and high salt, has been prospected. Through the review, although functional polymers, such as temperature resistant and salt resistant copolymers, instant polymers and amphiphilic polymers, have been successfully developed, the types of polymers used in the field are still limited. How to apply the research and development achievements of new polymers to on-site EOR is the key development direction. With the development of different polymer types, further research on polymer flooding mechanism is needed.

Wang-17 Block of Wangji Oilfield is the first zone in China to carry out polymer flooding EOR test with multi-stage heterogeneous profile control slug in oil reservoirs with low-medium permeability. The objective is to form the matching technology of chemical flooding in small fault block and low-medium permeability reservoirs, and to lead, demonstrate and use the remaining Class I and Class II chemical flooding reserves of 3 512×10⁴ t in Henan Oilfield. The keys of the technology are adaptability of flooding agent to reservoir, effective plugging of extreme water-consuming layers and well pattern adjustment. Therefore, starting with the adaptability of polymer and preformed particle gel（PPG） to reservoir, the grain size distribution of PPG and the factors affecting water absorption and swelling of viscoelastic particulate have been studied and the salt resistance, shear resistance and thermal stability have been characterized. Meanwhile, the relation between particle number and concentration, the possibility of injection, the oil displacement efficiency and the diversion rate of heterogeneous system have been evaluated. The results show that the optimized heterogeneous flooding system has better adaptability to low-medium permeability reservoirs. Field application has achieved the effect of increasing oil production and reducing water, which provides technical support and significant reference to EOR in the similar oil reservoirs.

In view of the reservoir conditions in a block of Changqing Oilfield with medium temperature, high salinity and low permeability, different temperature-salt resistant associative polymers（HAWSP series） with low relative molecular weight（720.42×10⁴ ~ 982.55×10⁴） and different contents of dodecylallyl tetramethyl ethylene diammonium bromide（TDAD） have been designed and synthesized. Then the molecular structure of the polymer has been confirmed by infrared spectroscopy. Under the conditions of this block, the reservoir adaptability of HAWSP series involving solution properties and application performance have been studied, and the field test has been carried out in this block. The results show that, compared with the salt-resistant partially hydrolyzed polyacrylamide（HPAM）, HAWSP series has better thickening capacity and similar aging stability（viscosity retention rate is greater than 85 % after aging for 60 days）. When the gas permeability is of 50×10^-3 μm², the associative polymer HAWSP-850 not only exhibits good injectability and conductivity, but also could present stronger sweeping ability in heterogeneous core with a permeability contrast of 4 times（low permeability is of 25×10^-3 μm²）, which can enhance the oil recovery by another 3.29 percentage points. Field tests show that the temperature-salt resistant associative polymer has better field adaptability. Compared with the conventional HPAM flooding system, it has a significant effect of reducing pressure and improving injection capacity and oil recovery. Associative polymer has important promotion significance of chemical flooding in low permeability reservoirs.

In-situ polymerization gel system is one of the important measures to alleviate reservoir heterogeneity. In order to solve the problem that the gelation time of in-situ polymerization gel system is too fast, taking polyvinyl butyral（PVB） as the wall material and the mixture of ethanol and water as solvent, the delayed gelation microcapsule initiator with ammonium persulfate as the active core has been prepared by interfacial precipitation method. Meanwhile, the performance of microcapsule regulating gelation time of in-situ polymerization gel system has been studied. By mixing 0.05 % ethanol solution of PVB with aqueous solution containing ammonium persulfate and 0.6 % compound stabilizer（OP-10 and Tween 80） at a volume ratio of 7:3, microcapsule initiator with an average particle size of 0.7~1.5 μm have been prepared, and the optimal concentration of ammonium persulfate is 0.2 % ~ 0.4 %. At 40 ~ 90 ℃, the gelation time can be longer than 30 h by adjusting the concentration of microcapsule initiator. Core test result shows that the microcapsule initiator can be successfully injected into the core with an average permeability of 50×10^-3 μm², and initiate the polymerization of in-situ polymerized gel system to produce effective plugging. The in-situ polymerization systems with initiator microcapsules can be injected into reservoirs with an average permeability of 50×10^-3 μm², and initiate the polymerization of in-situ polymerization gel system to produce effective plugging. The enhanced oil recovery（EOR） result indicates that the oil recovery increases by 20.24 % after the gelation of the in-situ polymerization gel system.

In order to explore the medium-high permeability reservoir with the permeability of （200~1 000）×10^-3 μm², the rheological behavior, thermal stability, viscoelasticity, and propagation performance of three kinds of polymer（linear polymer, hydrophobic association of partially hydrolyzed polyacrylamide（HAHPAM）, and active polymer） acting as the chemical flooding agents in Bohai Bay, are studied under the simulated reservoir condition. Results of rheological behavior indicate that HAHPAM and active polymer solutions exhibit shear thickening at low shearing rate（simulation of deep reservoir, 5.88~14.42 s^-1）, and all three polymers show shear thinning at high shear rates（simulation of immediate vicinity of wellbore, 149.9~223.4 s^-1）. The oscillation frequency measurements show that HAHPAM and active polymer have larger elasticity, and their storage modulus are greater than their loss modulus. Results of sand-pack flow experiments show that linear polymer and active polymer can propagate better in porous media to achieve in-depth conformance control, whereas HAHPAM shows poor propagation behavior. The results of TEM and LPSA indicate that HAHPAM shows larger aggregation sizes（1.22 μm）, and the compatibility of linear polymer（0.28 μm） and active polymer（0.52 μm） with pore throats（4 μm） of reservoirs is better than that of HAHPAM. The results show that for the target reservoir, the polymer has better adaptability to the reservoir, followed by the linear polymer, while the hydrophobic association polymer has poor adaptability to the reservoir. The selection of polymer for polymer flooding in offshore reservoirs needs to consider the rheological properties of polymer, reservoir adaptability, and molecular microstructures so as to establish a multi-scale evaluation method for polymer screening. This study has a certain significance for screening polymer for polymer flooding in offshore oilfields.

In order to find out the formation mechanism and distribution of residual oil after water flooding and tap the potential of residual oil, a parallel pore micro model has been established based on N-S equation. Phase field method has been used to track the phase interface in the process of water flooding. The distribution characteristics of residual oil after water flooding under different wall wetting conditions have been studied. The residual oil after water flooding has been exploited by mobility ratio improved by polymer flooding, interfacial tension changed by surfactant or wettability inversion occurred. And the effects of different mobility ratio and interfacial tension on the micro flow of residual oil in parallel pores after water flooding have been studied. The results show that when the rock surface is water-wet, the residual oil mainly stays in the large pore channels in parallel pores after water flooding. The polymer flooding improving the mobility ratio can effectively displace the residual oil in the pore channels, entirely. When the rock surface is oil-wet, the residual oil after water flooding mainly stays in the wall of parallel pores and small channels. It is difficult to displace the residual oil in the small pore by improving the mobility ratio. However, after changing wettability by surfactant, the residual oil is stretched into oil droplets and congregated, and finally the residual oil saturation is reduced. The lower the mobility ratio or interfacial tension, the higher the oil displacement efficiency. This study reveals the distribution and displacement mechanism of residual oil in parallel pores after water flooding, and provides an important theoretical basis for the effective exploitation of reservoirs by water flooding.

In order to improve the viscosity-increasing performance of polyacrylamide solution in high temperature and high salt reservoir, the common method is to introduce association and salt-resistant monomer in the synthesis process. However, with the development of monomer synthesis technology, some temperature-sensitive copolymers appear. At present, there are few researches on the oil displacement performance of these polymers. For this reason, conventional binary copolymer AM-NaAA and temperature sensitive terpolymer AM-NaAA-RTM have been selected, and the basic physico-chemical properties, viscosity enhancement, temperature resistance and viscoelasticity of the two polymers have been compared. The results show that after the introduction of temperature sensitive monomers, when the temperature is below 60 ℃, with the rise of temperature, the viscosity of AM-NaAA-RTM decreases; but when the temperature is above 60 ℃, its viscosity increases with the rise of temperature; while at 85 ℃, the viscosity of AM-NaAA-RTM is more than double that of AM-NaAA, which is conducive to expanding swept volume of high temperature reservoirs. In addition, the viscoelasticity modulus of AM-NaAA-RTM is higher than that of AM-NaAA. Therefore, the oil flooding effect of temperature-sensitive polymer is better than that of conventional AM-NaAA polymer, which is expected to be applied in chemical flooding of high temperature and high salt reservoirs.

Xinjiang Nine-Six reservoir is a shallow and high-heterogeneity heavy oil reservoir. In the later stage of steam flooding, there are some problems such as high water cut, low oil-steam ratio, serious overlap and channeling of steam, low sweep efficiency and low oil recovery. In order to further enhance the oil recovery, the profile control performance through the application of in-situ gel system in the late stage of steam flooding has been studied. Firstly, the gelling strength, microstructure and temperature-resistance behavior of the in-situ gel have been estimated by frequency-elastic modulus scanning, electron microscope scanning and thermogravimetry（TG-DTG） respectively. Then the 3D physical simulation experiment has been carried out to investigate the gel’s profile controlling performance. The experimental results show that after the addition of thickened cellulose in the original system, the gel’s elastic modulus increases from 96.5 Pa to 316 Pa, indicating the great increase of gel strength. The microstructure of the gel is tighter, the cross-linking is stronger and the stability has been enhanced. Weight retention rate of the gel is higher than 90 % as the temperature increases to 160 ℃, and the temperature-resistance has been improved. In the later stage of steam flooding, after injection of gel solution into high-permeability layer and its transformation into gel, the injection pressure and the oil/steam ratio increase remarkably while the water cut reduces dramatically. The sweep efficiency increases by 31.96 % and the oil recovery by 14.07 %. The in-situ gel can cement oil sand, and block the channeling path of high-permeability layer, which effectively suppresses the steam channeling and overlap. Subsequently, the injected steam can easily enter the low-permeability layer to displace crude oil, resulting in the drastically increasing of sweep efficiency and oil recovery, and indicating the remarkable profile control performance in deep parts.

Due to high oil viscosity and severe heterogeneity, heavy oil reservoirs generally lead to the poorer oil recovery due to the early breakthrough and ineffective circulation of displacing fluids through the prevailing flowing channels. It is necessary to develop the oil-displacing agents or systems which can efficiently generate resistance at low viscosity to achieve better mobility control and significant heterogeneity control. Compared with HPAM, the abilities of the resistance factor generation, mobility control under homogenous condition and heterogeneity control under heterogenous condition of associative polymer（HAWSP） have been studied at a similar viscosity. The results show that, when at the similar viscosity, the resistance factor generated by HAWSP in the permeability range of （300 ~ 2 000）×10^-3 μm² is nearly four times of that generated by HPAM with the permeability of 300×10^-3 μm², and HAWSP has a significantly stable displacement front and obtains a higher EOR for oil with the viscosity of 110.7 mPa·s. When under the homogeneous conditions, HAWSP has similar behavior with HPAM in the aspects of polymer production and retention ratio. On the contrary, when under the heterogenous conditions, the former has a significantly higher retention ratio（63.4 %） than the latter（5.2 %）. When at a permeability contrast of 4 times, the fractional flow of HAWSP in the high and low permeability layers exhibits an obvious alternating movement, and HAWSP can enable subsequent water to maintain a high fractional flow in low permeability layer for a long time. When at a permeability contrast of 5 times, HAWSP can displace the most of the cluster-like residual oil trapped in the model, and the phenomenon of "drawing" and "oil bridging" can be also observed in the outer large flow channels. The results indicate that associative polymer has significant abilities to control mobility and adjust heterogeneity, which can also be demonstrated by associative polymer flooding field application in offshore oilfield. In a word, associative polymer has greater application potential in the development of heavy oil reservoirs.

In order to solve the problems of decline continues to increase,carry out the research on the factors affecting the development effect of polymer flooding in the later stage.There are some problems in the small faulted block reservoir He Er Duan of Shuanghe Oilfield, such as strong edge water energy shows low efficiency, irregular well pattern leads to fluid channeling,formation plugging results in a large drop in well fluid production and so on.In order to improve the development effect of polymer flooding in later stage and further enhance oil recovery.Studing the effect of cluster displacement under different injection-production parameters by numerical simulation technology,define reasonable injection-production ratio. The inhibition effects reserched single point cross-flow in different injection-production way by numerical modeling, and draw the best way. Study on radius of oil congestion in polymer flooding stage and come up with reasonable countermeasures,good field application effect had been taken.

For the reservoirs after polymer flooding, the heterogeneity is stronger and the remaining oil distribution is more dispersed, conventional chemical flooding in consequence is difficult to further improve oil recovery effectively. Therefore, a heterogeneous combination flooding system consisting of polymer, preformed particle gel（PPG） and highly effective surfactant has been designed according to the features of medium-high permeability sandstone reservoir in Ⅱx layers of Shuanghe Oil Filed after polymer flooding. Thereafter, the selection of flooding agent, evaluation of thermal stability and Optimization of injection mode have been studied. The experimental results showed that the obtained P/PPG/S system has excellent high viscoelasticity, ultra-low interfacial tension, and thermal stability, which can effectively improve reservoir heterogeneity, expand sweep volume and enhance oil displacement efficiency. Core displacement experiments showed that the oil recovery could further enhance by 27.8 % after the combination flooding of P/PPG system and P/PPG/S system under simulated reservoir conditions. Thus it provides a technical method for effectively enhancing oil recovery after polymer flooding in Shuanghe oilfield.

The heterogeneous composite flooding has been proved to be an effective development technology to greatly improve oil recovery after polymer flooding, and the reasonable well pattern adjustment is the main method to improve the performance of heterogeneous composite flooding. By numerical simulation, the well pattern form, well spacing and flow line transformation angle of well pattern adjustment in Ⅳ1-3 reservoir of Shuanghe Oilfield have been systematically studied, and the comprehensive comparison and demonstration have been carried out from technical and economic aspects. The results show that the viscosity ratio of injection system to crude oil and the heterogeneity of formation have a decisive influence on the adjustment effect of well pattern flow line. For Ⅳ1-3 reservoir of Shuanghe Oilfield, on the premise of making full use of the old wells, the adoption of five points well pattern and well spacing of 150 ~ 300 m, and the great adjustment of the flow line angle can further improve the performance of heterogeneous composite flooding in decreasing water cut and increasing oil production.

In order to solve the problems of serious heterogeneity, breakthrough of injected water along high permeability zone, low recovery percent of reserves and limited EOR capability of water flooding in the middle and low permeability fault-block reservoir of Wang-17 Block in Wangji Oilfield, the EOR technology of chemical flooding has been studied, and polymer and preformed particle gel（PPG） have been evaluated and screened. The slug structure, oil displacement efficiency and diversion rate of heterogeneous oil displacement system formed by compounding have been evaluated by physical simulation technology. And the slug volume and structure have been optimized by numerical simulation technology. It is confirmed that multi-stage heterogeneous profile control and slug polymer flooding can improve the recovery rate in Wang-17 Block by 8.25 percentage points. The field application has achieved initial results. This technology has been used for reference and popularized in the polymer flooding project of B238 Block in Xiaermen Oilfield.

For the oilfields in east China with long-term water injection development, the water injection efficiency is gradually reduced due to the developed high water consumption strip in reservoir. In order to define the influence factors of development of the high water consumption strip, taking northern Shuanghe block in Nanyang as the research object, the influences of injection rate, permeability ratio, permeability variation coefficient and formation coefficient on the development of high water consumption strip have been analyzed respectively. Combined with orthogonal experiment, the relative influence level of the four factors is compared. The results show that high permeability, low injection rate, high permeability variation coefficient and high permeability ratio are more likely to cause the problems. With a certain formation coefficient and injection amount, high permeability is in major. Through the orthogonal test, the permeability variation coefficient influences most, followed by permeability ratio and formation coefficient, and the injection rate influences least. This study provides some reference for the adjustment in the later stage of oilfield production.

In order to solve the problems in Wellblock-SN-1 in Junggar Basin such as high water cut in oil wells, poor water injection effect in some wells, and decline in permeability of oil and water wells after water injection with wastewater and other issues, the influencing factors of water flooding recovery of reservoir have been studied. By the water injection optimization numerical simulations and experiments such as damage by the injection water to core, core flooding and injection water quality indicator analysis, the formation damage by injection water have been studied from microscopic scale, core scale and macroscopic scale respectively, and the damage mechanism leading to the decrease of permeability in production and injection wells has been revealed. It is recognized that the formation damage caused by solid blockage in injection water is the main controlling factor leading to low oil recovery. It is found that the solid blockage not only affects the microscopic flooding effect, but also increases the mobility ratio and reduces the sweep efficiency. Therefore, the water quality of the re-injection of the reservoir in Wellblock-SN-1 is the main factor for the poor water injection efficiency. The suspended solid mass concentration should be treated as the primary water quality control index. The proposed multi-scale evaluation method improves the reliability of the results, and is helpful for improving the exploitation effect of oilfield water flooding. It can provide technical reserves for stable oilfield exploitation.

The influences of temperature, quartz sand, detritus and specific surface area of medium on thermal release caused by low-temperature oxidation of heavy crude oil of Jiqi Oilfield have been investigated by self-designed high-temperature and high-pressure heat tracking compensation equipment. The results show that the temperature is the significant factor regarding heat release induced by low-temperature oxidation of heavy crude oil. As the initial temperature increases, the increase in capability of oxygen consumption and heat liberated as well as the reduction in pressure. When the initial temperature is 160 ℃, the temperature is improved by 10.7 ℃ in the first 26 hours coupled with the pressure reduction of 2.26 MPa and 2.5 % of effluent oxygen concentration, showing obvious thermal effect caused by low-temperature oxidation of heavy crude oil. Both the increment in the specific surface area and the addition of quartz sand and detritus can promote the thermal release induced by low- temperature oxidation of heavy oil, thereinto, the specific surface effect of medium gives a small contribution to the thermal release of low-temperature oxidation.

In the later development stage of strong bottom water sandstone reservoir of Tahe Oilfield, the development effect of remaining oil between wells is poor, and the conventional EOR methods is inapplicable. In order to solve these problems, the feasibility of CO₂ flooding in this type of reservoir has been explored. By combining laboratory experiments, numerical simulation and conventional reservoir engineering, the CO₂ flooding mechanism for sandstone reservoir with strong bottom water has been studied, and the MMP of CO₂ used in Tahe sandstone reservoir with strong bottom water is determined to be 29.6 MPa, the main mechanism of CO₂ flooding is preliminarily defined to be such as swelling of oil and expansion of horizontal swept area, the dissolution and distribution ratio of CO₂ in oil and water is about 4:1, and the CO₂ flooding can increase the recovery by 12.5 %. All these show that CO₂ flooding in Tahe sandstone reservoir with strong bottom water is feasible. The research results lay a theoretical foundation for EOR technology of this kind of reservoir and provide a scientific basis for CO₂ flooding pilot test of Tahe bottom water sandstone reservoir.

The internal multiples are very developed in seismic data of QT area, which interfere with the effctive signal, reduce the signal-to-noise ratio and affect the imaging accuracy. In this area, the internal multiples and the primary wave are similar in the characteristics of the wave group, and the remaining time difference is small. This similarity makes it difficult for suppression. Therefore, the internal multiple has become one of the difficulties that constrain the fine exploration in this area. Based on the difference between internal multiple and primary waves, firstly, the characteristics of the internal multiple are analyzed from various aspects such as CMP gathers, velocity spectrum and stack section to determine the origin, speed and range. Then, the high-precision Radon transform method is adopted to suppress the multiples. The practical application shows that the high-precision Radon transform method gives a good suppression effect on the internal multiples in the seismic data of QT area, which has great significance to improve the imaging accuracy of seismic data in this area.

The traditional automatic control of CBM is easy to overshoot and lag, making the automatic control technology of CBM recovery just stay in the level of data acquisition and simple remote control. Therefore, the problems existing in the traditional PID control algorithm in the automatic control of CBM drainage is discussed, and the causes of over harmonic and lagging phenomenon are analyzed, so as to put forward the loose coupled automatic control technology of CBM wellbore flow rule model combined with PID control algorithm. The upper computer adopts digital analog multi parameters coupling to reduce the difficulty of automatic control, after that, initializes user instructions. In the loosens coupling algorithm, the digital analog parameters are used as the error range value to improve the efficiency of PID control and effectively make up for the shortcomings of traditional one. Loose coupling automatic control can also avoid the destructive development of single parameter control, which is suitable for many unique production modes of CBM, such as slow flow pressure reduction by constant casing pressure and constant production, and slow casing pressure reduction by steady flow pressure. It has a high popularization value in the automatic drainage of CBM.