川西坳陷须家河组(T_3 x)气藏再认识

RECOGNITION OF XUJIAHE FORMATION (T_3 x ) GAS RESERVOIRS IN WEST SICHUAN DEPRESSION

川西坳陷须家河组 (T3 x)上、下盆结构性沉积建造 ,控制生储盖层发育和早期非构造圈闭。持续生烃和压实封闭是普遍超压的主因 ,现代地压状况是晚期构造改造的结果。须三段厚大生烃泥岩作为压力封隔 ,须二砂岩段可能蕴藏很大资源。本文建立了川西坳陷T3 x成藏理论特征模型 ,用来预测气藏规模 (Dg) :Dg≈ f(E ,d) .f(SFU !) ,突出早期聚集与晚期构造相结合。主要矛盾是T3 x储层普遍超致密化 ,关键在于晚期背斜的造缝能力。由于地史中成藏、僵滞、重组等关系非常复杂 ,找到T3 x大储量气田要下大功夫 ,必须在成藏理论和勘探技术两个方面都有实在的进展。

The source-reservoir-caprock assemblage and early non-structural trap formation are controlled by the basin-structural sedimentary formations over and under T_3 x .The superpressures mainly result from sustained hydrocarbon-generation and compaction seal and the current geopressure circumstances are the result caused by late tectonic movements.Because the thick T_3 x 3 mudstones are not only the source rocks but also the pressure confining beds,the T_3 x 2 sandstones may be rich in gas resources.A theoretical characteristic pattern of T_3 x gas reservoir formation in West Sichuan Depression was set up,in which the combination of early accumulation with late structure is emphasized.The key factor is the fissure-formed capacity of the late anticline,because of a general super compactness found in T_3 x reservoir.Owing to the fact that the relation between the reservoir formation and the hydrocarbon stagnancy and retrapping was very complicated in geological history,it is not easy to find a gas field with large reserves in T_3 x .Therefore it is necessary to make a real development in both gas reservoir formation theory and exploration technology.This paper is written for above purpose.