叠合盆地油气藏形成、演化与预测评价

Hydrocarbon Reservoirs Formation,Evolution,Prediction and Evaluation in the Superimposed Basins

中国西部叠合盆地经历了多期构造变动和多旋回的油气成藏作用,油气成藏之后经历了后期构造变动的调整、改造和破坏,分布规律十分复杂。研究叠合盆地油气藏的形成、演化和分布对于提高叠合盆地油气勘探成效具有重要的指导意义。叠合盆地系指不同时期形成的不同类型的沉积盆地或沉积地层在同一地理位置上的叠加和复合。它们具有地层沉积不连续、地层构造不连续和地层应力应变作用不连续等三大判别标志。依据构造剖面上沉积地层年代的关联性将叠合盆地分为连续沉积型、中晚叠合型、早晚叠合型、早中叠合型和长期暴露型等五种类型。叠合盆地复杂的构造过程产生了多种类型的复杂油气藏。三种地质作用(剥蚀、断裂和褶皱)使区域盖层受到破坏,六种微观机制(渗漏、扩散、溢散、氧化、降解和裂解)导致了油气损耗。它们的联合作用形成了原成型、圈闭调整型、组份变异型、相态转换型和规模改造型等五种类型的复杂油气藏。叠合盆地功能要素组合控制着油气藏的形成和分布,主要的功能要素包括有烃源灶(S)、古隆起(M)、沉积相(D)、区域盖层(C)、断裂带(F)和低势区(P)等,它们在纵向上的有序组合(C/D/M/S)控制着有利的成藏层位;在平面上的叠加复合(C∩D∩M∩S)控制着有利的成藏范围;在时间上的同时联合(TC=TD=TM=TS)控制着有利的成藏期次(T)。叠合盆地后期构造过程的叠加复合导致了早期油气藏的调整、改造和破坏。构造过程叠加改造油气藏的基本地质模式是:强强叠加破坏、强弱叠加改造、弱弱叠加保护。构造变动破坏烃量受构造变动强度、构造变动次数、构造变动次序、区域盖层封油气能力和原始聚油气量等五方面因素的控制,建立了构造变动破坏烃量和剩余资源潜力与各主控因素之间的定量关系模式,为叠合盆地构造变动破坏烃量评价提供了新的方法和技术。叠合盆地晚期相-势-源复合决定着圈闭的含油气性。叠合盆地发生过多期成藏作用,但最后一期成藏作用的勘探意义最大;叠合盆地油气藏发生过多期调整和改造,但晚期条件的制约作用最为关键。叠合盆地多期复合成藏区和弱弱叠加保护区最有利开展当前油气藏勘探;在这一地区的油源通道上发育的圈闭、优相储层区中发育的圈闭、低势场中分布的圈闭的成藏概率高;依据近源-优相-低势复合控油气富集模式可以预测和评价最有利勘探目标的含油气性,优选钻探目标。叠合盆地的油气勘探需分四个层次展开。首先基于地质门限联合控油气作用搞清每一运聚单元内的油气生成量和损耗量,根据物质平衡原理预测有利的资源领域;其次在有利资源领域展开油气成藏功能要素的识别、演化历史恢复和控油气作用研究,基于功能要素组合控油气分布模式预测出多期复合成藏的边界、范围和概率;然后开展盆地演化历史与油气藏调整、改造和破坏作用的研究,基于构造过程叠合改造油气藏模式在有利成藏区带内预测出剩余资源较大的有利勘探区;最后在有利勘探区带内展开油气富集作用的研究,基于近源-优相-低势复合控油气富集模式预测出最有利的钻探目标。应用新理论新技术,预测了塔里木盆地和准噶尔盆地主要目的层最有利的资源领域、最有利的成藏领域和最有利的勘探目标区。研究结果表明:塔里木盆地台盆区和准噶尔盆地已发现的油气藏100%分布在理论预测的最有利成藏领域中得最有利勘探区带内;截止到2009年底,上列两个盆地已钻567口探井中得316口成功井100%分布在理论预测出来的最有利勘探目标中,其中日产油气量超过18t的高产井中得95%的相-势-源复合指数(FPSI)大于0.6。215口无油气的探井中,有24%～68%是功能要素不好,有5%～19%是构造变动破坏所致,有27%～57%是相-势-源复合不好。叠合盆地"要素组合控藏-过程叠加改造-晚期相势定位"的理论成果在塔里木盆地和准噶尔盆地的油气勘探实践中得到了较好的应用,就塔中隆起一地预测和评价出来的21个最有利的勘探目标中,经钻探证实100%获得了工业油气流。它们为近年来塔里木油田公司年均发现2.85亿吨油气储量和每年保持18%的储量增长提供了理论和技术支撑。

Multi-stages tectonic events and hydrocarbon accumulation happened and multi-stages adjustment, reconstruction and destruction happened after origin hydrocarbon reservoirs formation because of the tectonic events, the hydrocarbon distribution rule is very complex in the superimposed basin, Western China,. It is of great significance to improve the exploration effects of superimposed basin by studying the hydrocarbon reservoirs formation, evolution and distribution. Superimposed basin refers to the different types of sedimentary basin or strata superimposed and composited at the same geographical position at different time. There are three landmark characteristics, which are stratigraphic sedimentary discontinuous, stratigraphic structure discontinuous and stratigraphic tectonic stress and strain discontinuous. Based on the sedimentary chronologic age, superimposed basin can be divided into five types, which includes successive sedimentation, superimposition of sedimentation at middle and late stage, superimposition of sedimentation at early and late stage, superimposition of sedimentation at early and middle stage and long-term, exposition. There are many types of complex hydrocarbon reservoirs formed because of complex tectonic movements in superimposed baisn. Three geological functions （denudation, faults and folds） destroyed the regional caprocks, six types of micro-mechanism led the hydrocarbon loss, which are leakage, diffusion, effusion, oxidation, degradation and cracking. Their combination formed five types of complex hydrocarbon reservoirs, which includes origin, trap adjustment, component variation, phase transformation, and scale reconstruction. Functional elements combination controls the hydrocarbon reservoirs formation and distribution in superimposed basin. The functional elements mainly include; source （S）, palaeo-mountain （M）, deposition （D）, caprock （C）, Fault belts （F） and I.ow potential zones （P）. They not only can be described objectively, and also characterized quantitatively. Orderly combination （C/D/M/S） controls the favorable hydrocarbon accumulation layers in section, superimposed （C n D n M n S）controls the favorable hydrocarbon accumulation areas in plane, simultaneous jointed （TC=TD= TM= TS） controls the favorable hydrocarbon accumulation stages in time. Multi-stages tectonic movements superimposed at late stage led to the origin hydrocarbon reservoirs adjustment, reconstruction and destroyed in superimposed basin. The basic geological model of structural process superimposed reformed hydrocarbon reservoirs are strong-strong tectonic events superimposed destroyed hydrocarbon reservoirs, strong-weak tectonic events superimposed reconstructed hydrocarbon reservoirs, weak-weak tectonic events superimposed protected hydrocarbon reservoirs. Facies-potential- sources compo sited at late stage controls the oil saturation of traps in superimposed basin. There are multi-stage hydrocarbon accumulation events happed in superimposed basin, and the final phase of hydrocarbon accumulation effect of significance is greatest to exploration. There are multi stage hydrocarbon accumulations, adjustment and reconstruction happened in superimposed basin, but the latestage restrictions role is the key. The multi-stage hydrocarbon accumulation composited area and weakweak tectonic events protected area is the best favorable area for oil and gas exploration in superimposed basin. In these areas, there is high probability of hydrocarbon accumulation in the traps which developed in the near-source path, favorable reservoirs and low potential. Based on the near source-favorable facies- low potential composited control hydrocarbon accumulation model, the most favorable exploration area oil saturation can be predicted and evaluated and further optimum the drilling target. Oil and gas exploration need to follow the four steps. Firstly, figure out the oil and gas generation amount and loss amount at each hydrocarbon accumulation and migration unit by the geological threshold controlling hydrocarbon function, based on the material balance theory, predict the favorable resource area. Secondly, identify the hydrocarbon accumulation functional elements, evolution history recovery and control function in the favorable resource area, based on the functional elements combination control oil and gas distribution model, predict the boundary, scope and probability of multi-stage hydrocarbon accumulation composited. Thirdly, study the evolution history of basin and hydrocarbon accumulation, reconstruction and destroyed role, based on the tectonic events process superimposed reformed hydrocarbon reservoirs model, predict the favorable province with larger remaining resource in the favorable area. Finally, study the hydrocarbon accumulation function in the favorable province, based on the near source-favorable facies-low potential composited control hydrocarbon accumulation model, predict the favorable exploration targets. Used the new theory and technology, predicted the most favorable resource area, hydrocarbon accumulation area and exploration area. The study results show that. 100%of discovered hydrocarbon reservoirs distributed in the predicted favorable area by new theory in the platform of Tarim basin and Junggar basin. By the end of 2009, 100% of 316 drilled successful well distributed in the predicted favorable area in these two basins, and 95% of wells which daily oil and gas production is more than 18tons, the facies-potential-source index （FPSI） is greater than 0.6. In the 215 wells with no hydrocarbon, 24%-68% of them is because the functional elements matching is not good, 5%-19% of them is because tectonic movements destroyed the origin hydrocarbon reservoirs, 27-57% of them is because the facies-potential-source coupling is not good. The theory of ＂ elements combination control hydrocarbon reservoirs-tectonic events process superimposition transform-facies-potential-sources couple at late stage＂ are good used to the Tarim basin and Junggar basin. Take Tazhong uplift as an example, 21 most favorable exploration targets have been predicted and evaluated, 100% of them have been proved by drilling well and got the commercial production. It supplied the theory and technology for discovered annual 2.85 tons of oil and gas reserves of Tarim Oilfield Company and annual 18% growth of reserves in recent years.