复合辫状河道期次划分方法与沉积演化过程分析--以鄂尔多斯盆地苏里格气田西区苏X区块为例

多期截切叠置的河道砂体中各单期河道的解剖向来是砂体建筑结构分析中的重点也是难点.如何从多期叠置的大块砂体中识别出单期河道并进行平面组合,进而完成辫状河的沉积演化过程分析是一个值得探索的课题.研究过程中,笔者充分利用岩芯、测录井、野外露头和现代卫星图片等资料,在标志层拉平基础上,通过“去压实效应邻井单期河道标定法”和“连续取芯验证法”,完成复合河道分期.在河道去压实效应过程中,采用了“松弛回弹技术”对河道进行了复位,为单期划分建立了基础.在垂向单期解剖基础上,结合现代沉积和经典地质概念模式,采用“单期砂厚中心连线法”,完成单期河道平面延伸轨迹的追踪和对比,然后按单期沉积发育顺序,完成复合辫状河道沉积演化过程与历史重建.研究结果表明,该方法将有助于揭示砂体空间叠置与局部砂体富集规律,提高砂体的钻遇率,便于后期水平井的大规模部署与地质导向等工程作业的实施,为油田生产实践提供理论依据.

Single Stage and Sedimentary Evolution Process Analysis of Braided River:A Case from SuX block of western Sulige gas field in Ordos Basin

Currently, Sulige gas field is in increasing production stage, the reservoir of He8 remember in Permian are more and more complex with the rolling exploration in progresses. Originally one well drilled into a thick channel sandbody, but the one of neighboring well was instead of inter-channel mudstone. The characteristics of fast facies transition have brought great challenges for large-scale implementation of horizontal wells. In fact, the main reason is that the overlay rules of sandbody are not clear. The reason of sandbody was not single stage, but multi-stage. The multi-causes, multi-stage and criss-cross stacked channel sandbodies in space were the main reasons which took shape the huge thick braided river sandbody. The center often is made of multi-stage channel sandbodies.
The Suxi block in Sulige gas field has been researched by predecessors who concluded that He8 member mianly developed braided river, and the result has been achieved wide recognition. The target bed thickness generally is 15~20 m. The study area located between the southeastern Su48 block and he northeastern Su47 block whose area is about 627 km2. The core and drilling well data can not only show the underwater deposition, but also no obvious delta front sedimentary, and the lower He8₂ sub-member mainly developed braided river deposits. The division time of stage is actually a part of the reservoir configuration. According to the previous configuration theory, braided river reservoir architecture can be divided into four levels (composite channel, single channel, channel bar, hyperplasia body), this study belong to the second level. The braided river of sedimentary micro-facies belongs to level, therefore, the identification of single stage river, compound, and sedimentary evolution analysis from composite channels can been researched based on the result of sedimentary micro-facies.
It is always the emphasis and difficulty of single stage fluvial sandbodies from composite braided riveway in reservoir architecture. Especially, it is the most difficult at the aspect of single stage identification and combinations from multi-stage stacked sandbodies, and the evolution of sedimentary braided river was finished. In the process of the research, the complex river stages were divided through continuous cores verification and “single stage calibration method based on removal compaction effects”, the riverways had been reset by “relaxation rebound techniques” based on removal compaction effects. The single stage riverway were tracked and compared after using “the sand thickness center line connecting method” based on modern sedimentary and geological models and theories, then, the results were confirmed by interference well testing which can confirm that the time of stage redefinition and the predicted results were reliable. Based on above the evolution and sedimentary history was researched according to the order of sedimentary development. The research result show that these research methods will help to reveal stacked sands, improve the rate of sand drilling, and it is also convenient to carry out large-scale deployment and post-horizontal well geosteering operations and to provide a theoretical basis so on for oil production practice simultaneously.