鄂尔多斯盆地东部二叠系山西组页岩气成藏条件与有利区筛选

Shale Gas Accumulation Condition and Favorable Area Optimization of the Permian Shanxi Formation,Eastern Ordos Basin

鄂尔多斯盆地东部榆106井区山西组页岩沉积在三角洲平原分流河道间沼泽、天然堤、决口扇远端与洼地环境。根据有机地球化学、物性、含气性、岩性实验分析,结合钻井、录井、测井资料与沉积相研究,开展了该区山西组页岩气成藏条件与有利区分布研究。山西组页岩有机碳含量较高,山二段平均5.28%,山一段平均3.02%,有机质类型以Ⅱ_2、Ⅲ型干酪根为主,有机质成熟度较高,R_o平均1.89%,生气条件优越。页岩孔隙度平均1.7%,渗透率平均0.0415×10^(-3)μm^2,平均含气量0.64 m^3/t,页岩单层厚度小,垂向上普遍与致密砂岩、煤层组成互层,累计厚度较大(平均达75 m),页岩渗透性较好而储集性能稍差。页岩脆性矿物含量平均49.9%,黏土矿物含量平均50.1%,黏土矿物含量较高,资源丰度普遍较低,但是页岩埋深小于3000 m,试气产能较高(0.64×10~4m^3/d),商业开发潜力较好。山二段有机质含量比山一段更高,含气性比山一段更好。主要基于页岩厚度与沉积相展布预测的山二段页岩气有利区呈北东向、南北向条带状展布,受分流河道间沼泽微相的控制。

The gas shales within the Permian Shanxi Formation were deposited in the interdistributary swamps, levees, distal crevasse splays and small lakes environment of a delta plain at the eastern Ordos Basin. The accumulation conditions and favorable area optimization of the Shanxi shale gas were investigated based on analysis of organic geochemistry, petrophysics, gas content and lithology with data of drilling, gas logging and wireline logging and depositional setting research. The shales have a relatively high total organic content, with an average of 5.28% in the second Member of the Shanxi Formation （Shan2 Member） and 3.02% in the first Member （Shanl Member）. The organic maturity of the shales is high with average Ro of 1.89% and the organic matters are dominant in type Ⅱ2、Ⅲ, which indicates an advantageous gas generation condition. The Shanxi shales have an average porosity of 1.7%, permeability of 0. 0415 × 10 3 μm2 and gas content of 0.64 m3/t, while the thickness of a single shale layer is relatively small and the shales are interbeded with tight sandstones and coals with a larger added shale thickness （up to 75 m on average）. These imply that the shales have rather good permeability with relatively lower storage capability. Brittle mineral content of the shales is 49. 9% on average, and clay content is comparatively high （an average of 50.1%）. The shale gas resource abundance is low. However, the shales have a buried depth less than 3000 m and acquired production of 6.4 thousand cubic meters per day by fracturing, which implies a good shale gas potential. Total organic content of the Shan 2 Member is higher than that of the Shan 1 and the gas content also higher than that of the Shan 1, which indicates that the shale gas is more enriched in the Shan 2 Member than in the Shan 1. Favorable areas of the Shan 2 Member predicted principally on shale thickness and depositional setting distribution show ribbon shapes principally trending northeast to southwest or north to south, which has a strong relationship with the distribution of the interdistributary swamps microfaces of a delta plain.