he carbonate reservoir has tight lithology and is operated at high temperature in S block. In order to improve the oil recovery, it is necessary to carry on the acid fracturing treatment to the target reservoir. According to the characteristics of the target reservoir, the acid fluid for acid fracturing was optimized and evaluated. Through the porosity and permeability experiment, the porosity of S block was 0.1%~2.0%, and the permeability was below 0.01 mD, which belonged to ultra⁃low permeability reservoir. According to the uniaxial compression test, the compressive strength of the reservoir was high, ranging from 40 to 70 MPa. X⁃ray diffraction showed that dolomite and calcite were the main minerals in the reservoir ( 80%~90% in total), with a small amount of quartz and clay (mass fraction was about 10%). The main acid was 20% hydrochloric acid, the thickener was 0.3% xanthan gum, and the dissolution rate of rock powder was about 90% when hydrochloric acid acted alone, and the main acid solution was hydrochloric acid. Taking into account that the reservoir lithology of carbonate rock in S block was dense and the formation temperature was 100~140 ℃, the viscosity of modified xanthan gum was about 10 mPa·s at 140 ℃. The modified xanthan gum was selected as high temperature resistant thickener.

At present, the polymer injection target of Lamadian oilfield has been shifted to the second type reservoir. Compared with the second type A reservoir,the second type B reservoir has serious heterogeneity and low permeability.For this reason,the study on the characteristics of polymer flooding seepage in the second type B reservoir is carried out.The results show that with the increase of core permeability,the iso⁃permeability point of polymer flooding relative permeability curve moves to the right and the span of two phases increases.Increasing the polymer molecular weight and the injection concentration can make the right end of the curve shift to the right.The polymer flooding resistance coefficient and residual resistance coefficient increase with the increasing of polymer solution concentration and molecular weight,while decrease with the increase of core permeability.There is a good correspondence between the polymer flooding resistance coefficient and the shunt rate.When the resistance coefficient reaches the peak,the shunt rate will reach the peak,and then the shunt rate of the high permeability layer will rise.The higher the molecular weight of the polymer, the higher the concentration of the solution,the greater the difference in permeability level,and the earlier the diversion rate of high permeability layer rises.

The re⁃injection block containing the sewage in the Xing 13 area is affected by the residual polymer,which leads to a decrease in the water absorption effect of the block and affects the development effect of the oil field. Therefore,the formulation and supporting process parameters of the depressurization and infusion injection of the sewage⁃containing block were studied.Firstly,the total water quality of injected water was analyzed; Then the petroleum sulfonate was used as the basic agent to screen the compounding agent and additives by measuring the interfacial tension;After the performance evaluation of the system, the indoor core flooding experiment was carried out to optimize the injection parameter.The results show that the optimal formulation of the anti⁃hypertensive surfactant is(mass fraction):0.7% petroleum sulfonate+2.0% HABS+0.5% absolute ethanol+1.0% NaCl,and the interfacial tension between the crude oil and the interfacial tension is 6×10-3 mN/m.In the core flooding experiment,the optimal injection rate is 0.15 mL/min,the optimal injection volume is 1 PV,and the optimal slug combination is 0.5 PV+0.3 PV+0.2 PV. Under different permeability conditions,the pressure rate is more than 24%.

In order to study the interlayer interference mechanism of water drive reservoir, the development plan of multi⁃layer co⁃production is developed. The core hole and permeability data of Gaotaizi core in the western Daqing central region are statistically analyzed, and the four⁃pipe parallel constant pressure displacement experiment is carried out with artificial cores with different permeability. The effects of injection and production pressure difference and permeability grade difference on recovery and water cut are studied. It is found that there is a reasonable injection⁃production pressure difference in core co⁃production with different permeability. The larger the permeability gradient is, the smaller the overall recovery is. The influence rule of permeability difference on interlayer disturbance is clarified from the mechanism, which provides theoretical basis for subdivision adjustment and water quantity adjustment.

The technology of water plugging in the oil well is more and more concerned with its low cost, low damage and long period of validity. But in the application, it is found that the effect of water shutoff and profile control of active crude oil in different blocks is quite different. Plugging measures effect is obvious in some fields, while in the others, it is very poor. The reason is that the content of gum and asphaltene in crude oil components of different blocks is quite different, and this substance will have a great influence on the emulsification effect of active crude oil. In order to improve the level of active⁃crude⁃oil water plugging technology fundamentally, on the basis of extensive investigation and research, the influence factors of emulsifier structures and crude oil composition on oil⁃in⁃water emulsion are studied, through the laboratory emulsification experiment and spectral analysis. It is concluded that the longer the length of the oil⁃wet carbon⁃carbon single chain of the Span series of emulsifier, the greater the viscosity of the emulsion. The existence of double bond is not conducive to the formation of emulsion and the emulsion viscosity is low. The composition of 5 aromatic rings in the gum is conducive to the dissolution of asphaltenes, while the planar arrangement of 5 aromatic rings will increase the viscosity of the emulsion.

The concentration of ions in the three element composite flooding is higher, the radius of the suspended particles is larger, the emulsification of the crude oil is serious, and the O/W emulsion is formed, which contains the polymer and the surface active agent. So, the viscosity of the three element composite flooding is larger and the composition is more complex. The above reasons make it difficult for the three yuan produced liquid to achieve better separation effect by conventional sedimentation treatment when oil and water separation is carried out. Through indoor sedimentation experiment, the settlement effect of the three surfactant polymer flooding under the conditions of different settling time and settlement temperature is studied, and effect and technical limits after mixing of three yuan and polymer flooding system are clearly defined. The experimental results show that three yuan of produced liquid in the blending of polymer flooding produced liquid, helps to reduce the three yuan produced liquid mixed with polymer flooding produced liquid is helpful to reduce the oil-water separation difficulty. From the analysis of water quality of mixed wastewater, the mixed three yuan extraction liquid and the polymer flooding recovery solution can not only reduce the sewage the treatment difficulty, but also be more conducive to the stable operation of the existing three yuan oilfield produced water treatment process. The optimum mixing ratio of three yuan production fluid and polymer flooding production fluid is1∶3,and the optimum mixing settlement time limit is 8 h.

The development of low permeable reservoir by means of alternate water gas injection can not only enlarge the swept volume, supplement formation energy, but also effectively prevent gas channeling. However, the problem of plug in gas well often occurs during the construction. By simulating the distribution of internal pressure and temperature in the wellbore of the gas injection well, the cause of freezing and plugging is analyzed. The main reason is the long time shut in of the gas injection well, resulting in the formation of fluid flowing back to the frozen plugging section and the CO ₂ reaction in the wellbore to form a frozen plug. Therefore, the well test method is used to calculate the pressure change rule in the wellbore after closing the well, and the time of formation fluid to freeze plugging is obtained. The results show that the gas injection rate has great influence on the wellbore temperature field distribution. As the injection speed increases, the low temperature in the wellbore extends longer. The phase state of CO ₂ gas can change within 1 000 m of the wellbore, which causes low temperature and high pressure in the wellbore and makes hydrate easily. Finally the limit closure time of injection well is determined to be 25 d according to the law of oil and gas twophase seepage and the law of pressure change after well closure.

The acidizing cleanup emulsion phenomenon is serious, and it can not enter the power off process. In view of the above problems, indoor simulation experiments were carried out to explore the influence of temperature, pH value, moisture content, the oil phase of the returned liquid, the water phase of the returned liquid, the iron-containing compound and the mud content on electric dehydration of returned acidizing fluids. It was found that when the impurities in the oil were less, the water phase and water content of the returned acidizing fluids had little effect on the electric dehydration, the increasing of the temperature was beneficial to the effluent demulsification, and neutral pH value was the most suitable condition for the demulsification of the returned fluids. The ferric hydroxide colloid which was wrapped with crude oil, sludge and free water in oil, forming a very high conductivity intermediate layer between the oil phase and the water phase, was the main cause of electric dehydrator trip.