临兴地区上古生界煤系致密砂岩气成藏条件分析

鄂尔多斯盆地东缘晋西挠褶带临兴地区致密砂岩气藏与邻区气藏相似,具有低平宽缓的构造背景和广覆式砂泥岩垂向间互分布的特征,但是由于处于不同的大地构造位置,其成藏条件具有显著差异性。针对研究区烃源条件、致密砂岩储层特征及封存条件,探讨致密气藏成藏特征。认为太原组主力煤层(8+9煤)和山西组主力煤层(4+5煤)是主力烃源岩,受紫金山构造岩浆作用影响,局部区域热演化程度进入干气阶段,为区内致密气藏提供充足的气源。岩相古地理和成岩相控制优质储层的发育和分布,本溪组向上到石千峰组,古地理环境由海变陆,频繁震荡的水体形成了多期次、多层位的储集体,潮汐砂坝、水下分流河道等粒度粗的砂体为优势致密储层,由北向南优势储层逐渐减少;砂岩储层总体孔渗性差,后期溶蚀作用对深部储层改造作用明显。煤岩、砂岩垂向组合决定了致密砂岩气藏的运聚模式,区内发育"源储接触"的原地匹配型气藏和受储层和运移通道双重控制的异地匹配型2类致密砂岩气藏,受断层和陷落柱影响而形成的微裂缝是垂向运移的主要通道。

Accumulation conditions of tight gas in the Upper Paleozoic of Linxing Block

Tight gas reservoir at Linxin area in the east margin of Ordos basin had similar characteristics with its neighboring area,which were with flat tectonic background and widely distributed sand-mud interbred.Because of the reservoir in different tectonic positions,its forming conditions are significantly different.Based on the analysis of hydrocarbon source conditions,tight sandstone reservoir characteristics and tight gas reservoir forming conditions,the study shows that the main source rocks are the coal seams of Taiyuan formation (No.8+9 coal) and Shanxi formation (No.4+5 coal).Affected by the Zijinshan tectonic magmatic,the main source rocks had entered into dry gas phase which provided sufficient supply for tight gas reservoir in some areas.The development and distribution of high quality reservoir was controlled by lithofacies paleogeographic and diagenetic.Multi-period and multi-layer reservoirs were formed which was resulted in by ancient geographical environment changes from sea to land and the water shocking frequently from the Benxi formation to the Shiqianfeng group.The advantaged tight reservoirs were the coarse grained sand bodies,which mainly included the tidal bar and underwater distributary channel sandstones,and decreased from north to south gradually.The vertical combination of coal bed and sand which were controlled by depositional environment determines the accumulation modes of the tight sandstone gas reservoirs.Porosity and permeability of sandstone reservoir was poor,but significant dissolution was effectively reconstructed on deep reservoir.Based on the vertical combination of coal bed and sand which controlled the migration and accumulation methods of sandstone gas reservoir,the tight sandstone gas reservoirs were divided into two types,one is in-situ matching gas reservoir in which source and reservoir were contacted,the other is remote marching gas reservoir which dual controlled by reservoir and migration channels.Micro-fractures were the main vertical migration and formed in the influence of faults and collapse column.