In order to understand the mechanism of CO₂ dissolved buried mechanism in high temperature and high pressure porous environment,physical simulation experiment was conducted to study CO₂ dissolved buried mechanism,mineralization buried mechanism and free buried mechanism in porous media by means of indoor physical model experiment.The results show that the solubility of CO₂ in formation water is mainly affected by temperature, pressure and salinity of formation water. CO₂ dissolved in formation water will mineralize with minerals in rocks, and the mineral content of rocks will change significantly before and after the reaction. The long core displacement experiment characterized the amount of free CO₂ storage and the oil displacement effect. The experiment reveal that CO₂ flooding in porous media has dual effects of burying and enhancing oil recovery.

In order to study the influence of cross?fracture on the mechanical properties and damage modes of deep shale, and better understand the damage evolution law of shale containing cross?fracture under high temperature and high pressure coupling, 15 groups of shale models containing cross?fracture with different inclination angles were established, and simulation experiments were carried out to study the stress?strain relationship, damage evolution and acoustic emission characteristics of the shale specimens. The results show that the compressive strength and modulus of elasticity of shale are negatively correlated with the inclination angle of the main cracks, and show an upward concave trend with the increase of the inclination angle of the secondary cracks, and the compressive strength of shale decreases significantly when there are cracks perpendicular to or close to perpendicular to the loading direction; the damage modes of shale specimens under the influence of cross?cracks are mainly divided into "X"?shaped damage, diagonal "N"?shaped damage, diagonal "W"?shaped damage, inverted "V"?shaped damage, damage along the main crack, "V"?shaped damage and "λ"?shaped damage; the fractal dimension of shale specimens is negatively correlated with the inclination angle of the main crack, and as the inclination angle of the main crack decreases, the value of fractal dimension tends to increase, and the corresponding damage pattern of the specimens is more complicated and the internal damage is more intense.

At present,there are few studies on the influence of medium and low water saturation on the capacity of free gas storage.Therefore, this study simulates the multi?round gas injection?soaking?production process through laboratory experiments; The laboratory experiment was carried out to simulate the process of multi?round gas injection?well soaking?production. Combined with the mathematical model and numerical simulation results, the research shows that the reservoir capacity increases with the increase of injection?production rounds, but the increase after single?round injection?production decreases rapidly.When the initial water saturation is higher than 50%, the increase of water saturation is beneficial to the reconstruction of gas storage, but the increase of injection?production capacity and storage capacity is relatively slow in the early stage of reservoir construction. When the initial water saturation is increased from 50% to 85%, the gas saturation is reduced by about 9.27% after 6 injection?production cycles. When the injection?production cycles are increased to 20,30,50 cycles, the free gas storage capacity is increased by about 0.51%,3.33%,6.61%, respectively. The research results are expected to provide reference for the evaluation of injection?production capacity and storage capacity of reservoir?type gas storage.

In recent years, with the continuous increase of foreign crude oil imports and the decline of domestic oilfield production, different oil products may need to be transported together by the same oil pipeline during the transportation process.The fourth oil pipeline of Qingtie is taken as an example. Combined with the actual parameters, the pipe wall is discretized by using the finite element analysis method of ANSYS and the hexahedral structural grid. The thermal structure coupling problem of the buried pipeline is solved, and the corresponding thermal stresses of the straight pipe section and the bent pipe section at different temperatures are calculated respectively. Based on the theory of fracture mechanics,the number of annual limit cycles under different service life is calculated, and the influence of temperature alternation on pipeline fatigue life is analyzed, which provides a theoretical basis for the safe transportation of cold and hot crude oil pipelines.

As the oil and gas industry strives to find better gas hydrate management methods, it is necessary to better understand the hydrate formation and plugging trend in multiphase flow.The high?pressure visual flow loop is used to study the formation of carbon dioxide gas hydrate and the properties of hydrate slurry under the flow conditions of complete dispersion and partial dispersion system.The results show that for the fully dispersed phase system with high water content, the contact area between gas molecules and water is larger, and hydrate can be fully generated, which has a great impact on the flow in the loop. For the two systems with different water content, because of the oil?water interface in high water content is damaged more violently, a large amount of hydrate is easier to block the loop.The oil?water interface in low water content can be supplemented after being damaged, so the risk of pipe plugging is low.

The infrared radiation observation experiment were carried out in the uniaxial loading process of four sandstones with different water contents. By studying the quantitative relationship between the infrared radiation information and stress of water?bearing sandstone, the influence of water on the infrared radiation characteristics of sandstone was revealed. The results show that with the increase of water content, the size of sandstone infrared anomaly area was larger, and the infrared anomaly phenomenon was more obvious. The mean value of infrared radiation counts of sandstone increased with the increase of the mean value of stress, and there was a linear relationship between them. After fitting the mean value of infrared radiation counts with the mean value of stress, it is found that the slope increases gradually with the increase of water content. The mean value of infrared radiation counts of sandstone was moderately correlated with water content in compaction and elastic stage, and highly linear correlation in plastic stage and post?peak failure stage (correlation coefficient up to 0.96).

Taking a heavy oil in Shengli Oil Field as the research object,the core was filled with porous medium in the core displacement instrument to simulate the formation conditions,and the aquathermolysis of heavy oil under different reaction conditions was studied.The results shown that the viscosity reduction rate of heavy oil can reach 20.8% only in porous medium by direct displacement,and the viscosity reduction effect is more obvious in porous medium system after the addition of amphiphilic catalyst for reaction.The displacement viscosity reduction rate after reaction in a low?temperature environment of 65 ℃ is 57.9%.However,the reaction in a low?temperature environment leads to an increase in the molecular weight of the asphaltene component,with the relative molecular weight of the asphaltene increasing from 5 244 g/mol to 6 690 g/mol.After the reaction is completed and maintained in a high?temperature environment of 265 ℃,the displacement has a better viscosity reduction effect,with a maximum comprehensive viscosity reduction rate of 96.0%.It provides an important guiding significance for the optimization of operating conditions of heavy oil aquathermolysis in the field application process.

The Bohai Sea is very rich in heavy oil reserves. At present,the thermal recovery rate is so low that the potential for tapping the potential is huge. It is of great practical significance to discuss the feasibility of gas injection exploitation in offshore heavy oil field. Through gas injection expansion experiments and multiple contact experiments, the effects of different gas injection media (CO₂,N₂,natural gas) on heavy oils with different viscosities in the Bohai Sea (general I?1, general I?2?A, general I?2?B) the solubilization,expansion,viscosity reduction effect and mixing mechanism.The experimental results show that the compatibility of CO₂ and heavy oil is better than natural gas and better than N₂, the viscosity reduction rates of CO₂ to the three types of heavy oil are 78%,85%,and 90%,respectively,and the viscosity reduction rates of natural gas to the three types of heavy oil are 29%, 69%,and 62%, respectively. CO₂ injection is more suitable for general I?2?B heavy oil, and natural gas injection is more suitable for general I?2?A heavy oil; the results of multiple contact experiments show that the mass transfer mechanism of CO₂ flooding is dominated by dissolution and condensate, the mass transfer mechanism of N₂ flooding is dominated by extraction and extraction, and the mass transfer mechanism of natural gas flooding is the condensate?extraction balance; in addition, the theoretical minimum miscible pressures are all greater than 43.00 MPa, so it is difficult to form miscible at the displacement front. The research results can provide important basis and technical support for gas injection to enhance oil recovery in Bohai heavy oil fields.

In order to determine the reasonable shape of the patching plate for the corrosion defects in the bottom of crude oil storage tank, this paper used finite element analysis to calculate the changes of the stress value in the corrosion defects after repairing different patching plate shapes, and then investigated the stress distribution and the safety factor value of the patching plate, and finally gave the best shape of the patching plate for the bottom of 20 000 m³ crude oil storage tank in Liaohe oil field. The results show that the best shape of the patching plate is a round patching plate. After repairing the corrosion defect, the stress value in the corrosion defect only decreases with the increase of the radius of the patching plate after the repair of the corrosion defect, and does not change with the change of the depth and radius of the defect. With the increase of the radius of the patch plate, the cost and safety of the patch plate will also increase, the specific size of the patch plate should be developed in accordance with the actual situation of the project. The results of the study can give theoretical guidance to the tank bottom repair from a scientific point of view.

In order to optimize the effect of Bohai oilfield regulation and flooding in B water injection development, the numerical simulation software of CMG reservoir was used to carry out optimization research on the effect of "weak gel+water?based microspheres" combined displacement to improve recovery,and according to the known geological reservoir properties of the oilfield,the actual three?dimensional geological model was established,and the historical fitting was carried out in combination with the previous production history.The factors affecting the modulation effect of single section of plugged weak gel modulation,single section of water?based microsphere modulation and driving and the factors affecting the modulation effect of "weak gel+water?based microspheres" were analyzed and optimized,and the related production indexes were predicted.The results show that the combined modulation effect of "weak gel+water?based microspheres" is significantly better than that of a single segment of plug modulation and driving.The optimal injection process parameters of the modulated blocking agent (weak gel) were selected through numerical simulation:the injection mass fraction is 0.50% crosslinker,the injection amount is 0.000 11 PV,the injection speed of A2H well is 240 m³/d,and the injection speed of A3H well is 200 m³/d.The optimal injection process parameters of the modulator (water?based microspheres) were selected through numerical simulation: the injection mass fraction is 0.30%,the injection amount is optimally 0.003 00 PV,and the injection speed of A2H and A3H wells is about 500~600 m³/d. This design scheme can effectively achieve the purpose of increasing precipitation and oil recovery.

Aiming at the periodic characteristics of severe slug flow an experimental study was carried out through the downward?riser system. Based on the experimental data and the variation of pressure in the pipe, the variation rule of the severe slug flow period was analyzed and verified reciprocally with the calculation model results. It turned out that the flow state in the tube would change under different experimental parameters such as the inclination angle of the downdip tube, the gas phase conversion velocity or the liquid phase conversion velocity. The time of the slug eruption and slug reflux was basically changeless on account of the height of the riser was invariant, so the period of severe slugging depends on the time of slug formation and slug outflow stages. And it was mainly affected by the inclination angle of downward riser, gas superficial velocity or liquid superficial velocity.

The types of volcanic rock reservoir space, reservoir physical properties and the main controlling factors were systematically studied by the method of reservoir physical property experiment, core casting thin section observation and X?ray diffraction test. The results show that the Yingcheng formation volcanic rocks in the Dehui fault depression have strong alteration, and the reservoir space is dominated by dissolution pores and dissolution fractures. The average porosity of tuff and dacite are 12.40% and 7.47%, respectively, and the permeability is less than 1.000 mD, belonging to type Ⅲ reservoirs. Gas?bearing formations can be further identified based on acoustic and resistivity logging methods. Lithology and lithofacies are the main controlling factors for the development of reservoirs, and lithofacies models of extrusive facies, extrusive facies and explosive facies were established in combination with the characteristics of seismic reflections. It provides an important theoretical basis for clarifying the mechanism of volcanic rock formation and the distribution of reservoirs in the study area.

To investigate the structure?function relationship of novel extended surfactants and the mechanisms of reducing interfacial tensions (IFTs) at oil?water interface, the interfacial tension values of 13?P series 13?P（I?C₁₃（PO） _x S,x=5,10,15,20）with different concentrations of NaCl and n?hexane to n?tetradecane at fixed concentration were measured by rotary drop interfacial tension meter. The result indicates that at higher numbers of PO（x=15,20), the n_min values become higher with increasing concentration of NaCl. At lower numbers of PO（x=5,10), the n_min values become lower with increasing concentration of NaCl. It reflects two mechanisms on reducing IFTs: Hydrophilic lipophilic equilibrium effect and hydrophilic hydrophobic group in size matching effect, both of which work together, and the size matching plays a crucial role at lower numbers of PO and HLB dominates at higher numbers of PO.

At present, the thermal recovery method is widely used in heavy oil recovery engineering, in which the high temperature and pressure wet saturated steam is injected into the oil well from the steam injection pipeline, and the heat carried by it is exchanged with low temperature heavy oil, so as to improve the fluidity and permeability of heavy oil and realize recovery. Wet saturated steam dryness is an important parameter affecting thermal recovery effino recognized measurement method existent method. There is no recognized measurement method. At present, the commonly used method is manual measurement, but the measurement results of this method have serious hysteresis. In order to achieve the purpose of real?time monitoring of dryness, a new measuring method, matrix conductance method, under the condition of 10 MPa and 310 °C, a 26×26 wire mesh model was established to measure the dryness of wet saturated steam in a steam injection pipeline with an outer diameter of 76 mm and an inner diameter of 54 mm. The measurement principle of the matrix conductance method is introduced and the dryness algorithm model is established. The electric field simulation was carried out in Ansys Electronics software, the electric field between the layers was analyzed, and the results show that the suitable interlayer spacing is 2 mm. In order to improve the accuracy, the linear interpolation method is used to process the edge, and the actual measurement error is predicted; the overall error after primary linear interpolation is within 2.50%; after quadratic linear interpolation, the overall error is less than 1.10%.

For the under?expansion jet generated after the failure leak of high?pressure pipeline, the Birch theory model was used to replace the actual pipeline leak hole with a pseudo?source. Under different conditions of Hydrogen Blend Ratio (HBR), leak hole size and pipeline running pressure, the concentration field distribution, explosion hazard boundary and explosion hazard range of hydrogen?doped natural gas pipelines after leakage and diffusion were studied. The results show that with the increase of HBR, the aggregation of HDNG after leak diffusion is reduced, the explosion hazard range is gradually decreased and the distal hazard is reduced. However, the increase of HBR shifts the position of explosion hazard boundary downward and increases the proximal hazard. With the increase of leak hole size and pipeline pressure, it will increase the influence area of HDNG after leak diffusion, which will move the explosion hazard boundary position upward and increase the explosion hazard range gradually and increase the distal hazard.

Aiming at the problem of wax deposition in gas well exploitation of offshore HPHT gas reservoir, the gas?liquid?solid and fluid phase equilibrium theory and method of throttling effect principle was used to reveal the wax deposition mechanism of the abnormal high temperature and high pressure gas well, and it was found that wax deposition in high temperature and high pressure gas wells mainly occurs at the position of the oil nozzle where the temperature drops sharply when the wing valve of the gas well is closed. According to the phase equilibrium theory, the phase state of the original formation fluid in HPHT gas well was recovered and characterized, and the phase state change characteristics of gas?liquid?solid three?phase fluid, wax precipitation mechanism and process were described accurately. Based on the phase equilibrium model, the wax location, fluid composition change and the influencing factors of wax deposition were analyzed. It was reasonable to explain that the mechanism of wax precipitation in HPHT gas well is the transient phase transition from gaseous to liquid and then to solid due to the rapid change of temperature and pressure, and the corresponding prevention and control strategies are put forward.

Standalone screen sand control method is one of the most commonly used sand control method for oil and gas wells. With the deepening of oil and gas field development, the working environment and its own conditions of the independent screen sand control system have changed. Affected by high temperature and high pressure, external load, corrosion, fluid erosion and other factors, it is easy to cause sand control failure, which seriously affects the normal production of oil and gas wells. In this paper, long?term mine practice and theoretical analysis are taken to investigate the reasons for sand control failure. It is considered that the main causes of sand control failure are sand control packer failure, sealing mechanism failure and sand control screen tube failure, among which sand control screen tube failure is the most likely to occur. Screen erosion, screen corrosion, geological factors and special operations are the main factors leading to the failure of sand control screen. Through the in?depth analysis of the causes of sand control failure in oil and gas wells, it provides an important basis for taking preventive measures to avoid sand control failure and affecting production.

Most of the oil fields in China have entered the middle and late stage of exploitation, and the well produced fluid has a high water content. FRP pipes are widely used in surface gathering system of oilfield because of their excellent corrosion resistance. At the same time, in order to save heating energy, low?temperature transportation process can be used to transport high water?cut crude oil, but the possible adhesion problem of crude oil is a serious threat to system safety.Therefore, it is important to investigate the interfacial properties of FRP pipe wall/crude oil to reveal the adhesion mechanism of low?temperature transportation of crude oil with high water?cut. The interfacial properties of crude oil on the FRP surface and stainless steel surface were investigated based on the contact angle apparatus. In the aqueous phase, the contact angle of oil droplet on the solid surface increased with decreasing temperature, and the contact angle of oil droplet on the FRP surface is larger than that on the stainless steel surface. The interfacial tension of oil droplet increased with decreasing temperature in the aqueous phase, and compared to the stainless steel surface, the adhesion work of oil droplet on the FRP surface is lower. And the cohesion work of oil droplet decreased with increasing temperature in the aqueous phase. Crude oil is not easy to adhere to the FRP pipe in the gathering system, FRP pipe is more conducive to the implementation of low?temperature transportation process.

As a universal low temperature gathering and transportation boundary condition,the wall sticking occurrence temperature (WSOT) has been widely promoted and applied in the oilfield in the late stage of high water cut development. When the oil gathering temperature is higher than the WSOT, the pipeline operates smoothly, otherwise the pressure drop of most pipelines increases significantly, but some of the pipeline pressure drop changes are not obvious. Through the field cooling experiment, it was found that in the process of the oil gathering temperature gradually decreasing to 6,8,10 ℃ and 12 ℃ below the gel point, the wellhead back pressure has experienced four stages of smooth operation, small fluctuation, low frequency large fluctuation and high frequency large fluctuation, and there are several "restart" processes in the pipeline when the gathering temperature is too low. At the same time, the gas injection experiment under different gas?oil ratio was further carried out, and the results show that when the gas?oil ratio is 40,80,160 m³/t, the pipeline can run stably at the gathering temperature 3,4 ℃ and 6 ℃ lower than the WSOT.

In the environment of CO₂ enhanced recovery (CCS?EOR), the corrosion cracking behavior and mechanism of X70 pipeline steel under different CO₂ pressures were studied. The on?site environment was simulated by using a high?pressure reactor and a simulated produced aqueous solution; the corrosion rate and corrosion mechanism of X70 pipeline steel in the CCS?EOR environment were investigated by electrochemical experiments; the corrosion cracking behavior of X70 pipeline steel under simulated environment was investigated by slow strain rate tensile experiments; finally, the corrosion cracking behavior of X70 pipeline steel under different CO₂ pressure was analyzed by scanning electron microscope. The results show that the corrosion rate of X70 pipeline steel increases with the increase of CO₂ pressure; the corrosion product film produced on the surface of X70 pipeline steel can not protect the metal matrix, and intensify the local corrosion; under the influence of the corrosion product film, the increase of CO₂ pressure makes X70 pipeline steel stress corrosion susceptibility increases; and the corrosion cracking of X70 pipeline steel is also affected by the metal surface cracks.

Energy shortage and environmental pollution have always been the focus of the world's attention. The use of oil, natural gas, and electricity to heat crude oil has high energy consumption and serious environmental pollution. Solar energy, as sustainable and clean energy, has become the focus of researchers from all over the world.Thus, a solar heating crude oil system was designed, and safe and easily available air was selected as the heat transfer fluid. The system consists of a solar receiver, a heat accumulator, a crude oil heat exchanger, and an electro?thermal furnace. The heat receiver receives solar radiation and the temperature rises. The air passes through the heat absorber to obtain high temperature, and the high temperature air enters the heat exchanger to heat the crude oil. A mathematical model for the analysis of the thermodynamic performance of the solar heating crude oil system was established, and the model was verified. Then, the Aspen Plus software was used to conduct thermodynamic analysis of the heatingprocess. The results show that the compressor and the preheater are the components with large exergy loss. When the pressure ratio of the compressor is 2.7, the system reaches its best state. At this situation, the thermal efficiency is 72.35%, the exergy efficiency is 73.89%, and the waste heat recovery efficiency is 72.33%.