YB地区须家河组须三段钙屑砂岩气藏成藏主控因素——以X7井为例

Main controlling factors of gas accumulation in the calcarenaceous sandstone reservoirs in the 3^(rd) member of the Xujiahe Formation in the YB area: A case study of X7 well

钙屑砂岩一般都致密,被认为是非储集岩类。2012年2月,中国石化勘探南方分公司在四川盆地YB地区所钻X7井在上三叠统须家河组须三段获得高产工业气流,薄片鉴定确认储层岩性为钙屑砂岩,由此点亮了钙屑砂岩储层油气勘探的希望。为此,通过对YB地区高产气井——X7井产层段岩石学特征、储集空间特征、储层物性特征、储层电性特征、储层地震响应特征分析,建立了YB地区上三叠统须家河组须三段钙屑砂岩气藏的成藏模式:钙屑砂岩分布+有利的成岩作用(包括早期短期暴露溶蚀作用以及晚期有机酸溶蚀作用)+构造裂缝发育带+合理断层匹配。并结合沉积相、地震属性分析和裂缝分布研究成果,对X7井附近须三段储层进行了综合预测。结果显示:油气富集区主要集中在钙屑砂岩发育带叠加构造裂缝发育带。在此基础上,提交了3口开发建议井井位。

Calcarenaceous sandstones are generally believed to be tight and thus non-reservoirs.In February 2012,after well test was done on the X7 well in the YB area of the Sichuan Basin by the Sinopec Southwest Branch Company,a high-rate industrial gas flow was obtained in the 3rd member of the Upper Triassic Xujiahe Formation.Thin-section observation showed that the reservoirs are mainly composed of calcarenaceous sandstones.Based on the comprehensive analysis of the petrophysical features,reservoir space characteristics,poroperm characteristics,electrical properties,and seismic responses,a gas accumulation pattern is recognized,i.e.,calcarenaceous sandstone distribution plus favorable diagenesis(early short period exposure and dissolution and late organic acid dissolution) plus structural fracture development zone plus suitable timing of faulting.Reservoir prediction was also made through the integrated analysis of sedimentary facies,seismic attributes,and fracture distribution.It shows that hydrocarbon accumulation mainly occurs in the areas where both calcarenaceous sandstones and structural fractures are highly developed.Proposals were presented for the emplacement of three wells based on these understandings.