四川盆地西部须家河组砂岩储层成岩作用及致密时间讨论

运用沉积及成藏理论对四川盆地西部地区须家河组砂岩的岩石类型、成岩作用及其成藏时间研究表明:砂岩储层的主要成岩作用有压实和压溶作用、胶结作用,溶蚀作用、破裂作用以及自生矿物的沉淀作用.压实作用是砂岩粒间孔隙减少的主要因素,然而,方解石的强烈胶结作用以及石英的次生加大作用是造成须家河组砂岩储层致密的关键因素.方解石胶结物和石英次生加大包裹体的温度测定表明方解石胶结物主要发育在100℃～140℃之间,石英次生加大主要发生在80℃～126℃之间,在此温度区间,有机质演化已到了成熟期,并在60℃～80℃之间就开始发生运移.因此,砂岩储层的致密时间晚于天然气的生成和运移时间,砂岩储层的致密时间应该在燕山构造活动期,大约在1.5×10~8 a左右.

DISCUSSION ON THE DIAGENESIS AND TIMING OF TIGHT SANDSTONE RESERVOIR IN XUJIAHE FORMATION, WESTERN SICHUAN BASIN

Tight sandstone reservoir of Xujiahe Formation in Western Sichuan Basin is a main target for natural gas exploration. Detailed study showed that the main types of diagenesis in the sandstone reservoir are compaction, pressure solution, cementation, fracturing and authigenic clay mineral precipitation. Of the diagenesis,the compaction is the major factor caused the decrease of inter-particle porosity. Based on the study of thin section,SEM and fluid inclusion,it is indicated that the key factors influencing the reservoir quality are massive cementation of calcite and quartz overgrowth,although the question of the mechanism of tight sandstone reservoir is still debata-ble. The temperatures determined by calcite cements fluid inclusions range from 100 ℃～140℃, and the temperatures of quartz overgrowth fluid inclusions from 80 ℃～126℃. The kerogen has become mature in this temperature span and the natural gas has been entered into the reservoir. It is obviously that the timing of tightness of sandstone reservoir is later than the migration of natu-ral gas. According to the relationship among gradient of geo-temperature, burial depth and inclu-sion temperature,the time of formation of tight sandstone reservoir should be 150 Ma of the Yan-shan tectonic period. The time of calcite cement precipitation also indicates that the formation of secondary porosity in sandstone reservoir is not the result of dissolution from organic acids.