【作者】 赵明国；

【导师】 刘永建；

【作者基本信息】 大庆石油学院 ， 油气田开发工程， 2008， 博士

【摘要】 随着我国油气勘探开发程度的不断提高,优质油气田的储量和产量逐年减少,低渗透油气田的储量和产量所占比例则逐年增大,已成为当前以及今后我国油气增储上产的主要资源。由于低渗透储层物性差,孔隙喉道细小,具有拟启动压力梯度等特点,注水压力高,吸水能力差,油井注水开发见效慢。油井见水后,产油和产液指数下降快,这给油田的稳产和增产造成了很大困难,如何有效开发特低渗透油藏是目前国内外面临的主要问题。本文针对大庆龙虎泡油田高台子特低渗透油藏,利用室内实验及数值模拟,开展特低渗透油藏CO₂驱可行性研究。在模拟地层条件下,利用室内实验测定和相态方程计算相结合,研究了CO₂驱后油气相态变化规律,随CO₂注入量增加,地层油溶解油气比、饱和压力、体积系数、收缩率、平均溶解系数和膨胀系数增大,粘度和密度降低,泡点压力、露点压力、临界压力升高,临界温度降低,相态图两相区面积增大,等液量线的间隔增大。利用细管法测定原油与CO₂的MMP为20.3MPa。在此基础上,进行了水驱、CO₂混相驱和非混相驱油实验,结果表明:随着CO₂注入压力增加, CO₂突破时采收率、最终采收率、CO₂换油率、CO₂注入能力逐渐地增大;CO₂突破后,生产气油比增加,压力越高,生产气油比越大;CO₂混相驱采收率高于水驱,非混相驱采收率低于水驱;注气能力与注水能力之比为16.463以上。利用一系列实验研究了高台子地层CO₂驱油机理,定量提出了某些机理对驱油效率的贡献值。将CO₂注入油层后,原油及束缚水中溶解大量的CO₂,在地层条件下,原油粘度降低36.73%,原油体积膨胀20.53%,束缚水体积增加5.97%;当地层压力降低后,CO₂形成游离气,产生膨胀能;随着CO₂注入压力增加,油层条件下的气驱时油气界面张力下降;根据驱替压差和驱出流体体积的曲线,确定特低渗透油藏多相流时水驱启动压力梯度为CO₂驱的2.9倍,注入CO₂可降低地层的启动压力;CO₂驱后,岩石孔隙结构发生变化,渗透率提高4%¹3%,岩石亲水性增强;改善相对渗透率,气相端点相对渗透率比水相端点渗透率低2.58倍以上,气油两相区范围高于水油两相区。根据龙虎泡油田高台子油层试验井区地质特征、井网状况及开发现状,应用PETREL地质建模软件建立了相控地质模型。采用Eclipse中的组分模型对CO₂注入方式、井网部署、注采压力、注采方式等进行了模拟。推荐方案为:井网加密方式采用井间加密,反九点法同步连续注气;注气压力为30MPa以上;采油井流压控制在2³MPa左右。推荐的CO₂驱方案模拟10年内采收率可达到33.07%,较水驱方案可提高20%以上。可见,大庆龙虎泡油田高台子特低渗透油藏采用CO₂驱是可行的。更多还原

【Abstract】 The reserve and production of high quality oil-gas field are decreasing with the improvement of exploration and development. The low permeability oil-gas field accounts for larger and larger proportion of oil production. The low permeability deposits have become the main resource to increase reserve and production now and in future. Due to the poor physical property, small size of pore and throat, high capillary force, a threshold pressure gradient exists in the low permeability reservoir. As a result, the water injection pressure is high, the water absorption capacity is poor, and the speed of water injection response is slow. With breakthrough of water in oil wells, the oil and liquid productivity index will decrease rapidly, which cause great difficulty to the stabilization and enhancement of oil production. How to develop effectively the ultra low permeability reservoir is a major problem confronted in the world at presentThe feasibility of CO₂ flooding in Gao Taizi ultra low permeability reservoir of Long Hupao oilfield were studied by laboratory experiment and numerical simulation in this dissertation. At the simulated conditions of Gao Taizi formation, the variation law of oil-gas phase behavior was studied through the combination of laboratory experiment and computation on phase state equation. The critical temperature of the formation crude from Gao Taizi formation was 600℃and the critical pressure was 39.846 MPa. With the increase of CO₂ injection volume, the bubble point pressure, dew point pressure and the critical pressure increased, the area of two-phase region increased, the interval between equivalent fluid lines enlarged. As the injected volume of CO₂ increasing, the GOR, saturation pressure, formation volume factor, volume shrinkage, compressibility coefficient, average solubility factor and expansion coefficient of the formation crude from Gao Taizi oil layer increased, while the viscosity and density declined.Slim tube experiment showed the MMP of crude oil and CO₂ was 20.3 MPa, higher than the formation pressure. Experiments of water flooding, CO₂ miscible and immiscible displacement were carried out, obtaining the following results: the recovery at CO₂ breakthrough, ultimate recovery, conversion rate from CO₂ to oil, CO₂ injectivity increased gradually with the increase of CO₂ injection pressure; After the CO₂ breakthrough, the GOR would increase, and the higher the injection pressure, the greater the GOR; the recovery of CO₂ miscible was higher than that of the water flooding, while the recovery of CO₂ immiscible was lower than that of the water flooding; the injectivity of CO₂ flooding was greater greatly than that of the water flooding, the injectivity ratio of gas to water was more than 16.463.A series of experiments were carried out to investigate the mechanism of CO₂ flooding in Gao Taizi formation, and the contributions to oil displacement efficiency of some mechanisms were decided quantificationally. With the injection of CO₂ into the formation, the oil and the irreducible water dissolved large amount of CO₂. At the formation condition, the viscosity of oil decreased 36.73%, the volume of oil increased 20.53%, the volume of irreducible water increased 5.97%, this portion of water became into flowing water; along with the reduction of formation pressure, CO₂ became into free gas, generating expansion energy; with the increasing of CO₂ injection pressure, the interfacial tension reduced. The interfacial tension was 3.868mN/m when CO₂ was injected at the formation pressure. When the pressure rised to miscibility pressure, the interfacial tension decreased to 2.598mN/m, and misible flooding occurred when the pressure exceeded the miscible pressure. The thereshhold pressure gradient was determined according to the relationship curve of the displacing pressure differential and the displaced fluid volume. The thereshhold pressure gradient of water flooding was 2.9 times to the CO₂ flooding, and the injection of CO₂ decreased the thereshhold pressure, increasing the injectivity; the rock pore structure changed after CO₂ flooding, the permeability increased 4¹3%, the rock hydrophilicity became stronger; the relative permeability was improved, the relative permeability at the end-point of gas phase was more than 2.58 times lower than that at the end-point of water phase, the two phase region of gas flooding was wider than that of the water flooding.According to the geological characteristic, well pattern and development status of the test area of Gao Taizi oil layer in Long Hupao oilfield, facies-controled geological model was established by using PETREL geological modeling software. The CO₂ injection mode, well pattern arrangement, injection and production pressure, injection-production pattern, etc. were simulated by the compositional model in Eclipse. The recommended scheme was inter-well infill, inverted nine-spot gas injection; gas injection pressure being above 30MPa; the flowing pressure in oil well being controlled at about 2³ MPa; synchronous and continuous gas injection. The simulated recovery could arrive at 33.07% in 10 years according to the recommended CO₂ flooding scheme, more than 20% higher than that of the water flooding scheme. Therefore, it is feasible to produce Gao Taizi ultra low permeability reservoir of Long Hupao oilfield by CO₂ flooding.更多还原