川东北元坝西部须家河组二段优质储层展布特征研究

Distribution of high-quality reservoir of the second member of Xujiahe Formation in western Yuanba area, northeastern Sichuan Basin

关键词:  岩石相  沉积微相  须家河组  储层发育主控因素  元坝西部  四川盆地东北部  致密砂岩气

Key words:  lithofacies  sedimentary microfacies  Xujiahe Formation  main controlling factors of reservoir development  western Yuanba area  northeastern Sichuan Basin  tight sandstone gas

摘要:

川东北元坝地区须家河组二段致密砂岩气资源潜力巨大，但储量探明率低、测试效果差异大，主要原因之一是致密砂岩储层非均质性强、优质储层分布规律不清。本文充分利用测录井、岩心及相关分析化验等资料，在分砂组刻画沉积微相展布的基础上，开展了须二段沉积演化过程、储层特征及其分布研究。结果表明：（1）元坝西部须二段经历了辫状河三角洲-滨浅湖-辫状河三角洲演化过程，沉积控制了砂体规模、粒度和矿物成分的空间变化；（2）须二段砂岩类型多样，整体致密，为低孔、低渗储层；储层物性与砂岩粒度，长石、石英和方解石胶结物含量等因素密切相关，这些因素主要受沉积和后期成岩作用控制；（3）须二段发育块状中粒长石岩屑砂岩和交错层理中粒石英砂岩两类有利岩石相，前者自西北向东南逐渐减薄、呈条带状展布，后者呈不连续土豆状，主体分布于西南部地区。

Abstract:

The potential for tight sandstone gas resources in the second member of the Xujiahe Formation in the Yuanba area of northeast Sichuan is enormous, but the proven reserves are low and the testing results vary widely, mainly due to strong heterogeneity of the tight sandstone reservoirs and unclear distribution pattern of high-quality reservoirs. This research makes full use of well logging, core samples, and related analysis and testing data to characterize the sedimentary microfacies distribution in the Second Member of the Xujiahe Formation based on sedimentary facies division, and carries out investigations into the sedimentary evolution process, reservoir characteristics, and distribution of the reservoirs.The results show that: (1) The second member of Xujiahe Formation in the west of Yuanba area has undergone an evolutionary process from braided delta to shallow lacustrine to braided delta, with sedimentation controlling the spatial variation in sand body size, grain size, and mineral composition; (2) The second member of Xujiahe Formation contains diverse types of sandstone, which are tight in the overall, and are low-porosity and low-permeability reservoirs. The physical properties of reservoirs are closely related to factors such as sandstone grain size, feldspar, quartz, and calcite cement content, which are mainly controlled by sedimentation and later diagenesis; (3) There are two favorable lithofacies in the second member of the Xujiahe Formation: massive medium-grain feldspathic lithic sandstone and cross-bedded medium-grain quartz sandstone. The former gradually thins from the northwest to the southeast and spreads in strips, while the latter is discontinuous and potato-shaped, primarily distributed in the southwestern region.