库车坳陷克拉苏构造带深层致密砂岩气成藏机制

为深化对克拉苏构造带深层致密砂岩气成藏机制的认识,开展了油气充注史和孔隙度演化史研究。以库车坳陷大北1气藏为例,运用流体包裹体岩相学和显微测温技术厘定油气充注史,采用定量回剥的方法恢复了储层孔隙演化史,根据两者的耦合关系明确了大北1气藏成藏机制。研究结果表明:大北1气藏存在3期油气充注过程,第1期为新近纪康村期至库车期的成熟原油充注,储层孔隙度为12%～14%,形成常规油藏;第2期为新近纪库车期高成熟油气充注,储层孔隙度为8%～10%,常规气藏与致密深盆气藏共存;第3期为新近纪库车末期至第四纪西域期的干气充注,储层孔隙度约为5%,形成致密常规与致密深盆复合气藏,西域期至今由于后期构造运动导致储层发育大量裂缝,气藏遭受改造,天然气沿裂缝在浮力作用下运移调整至构造高部位聚集。该研究成果进一步拓展了库车凹陷克拉苏构造带致密气勘探开发前景,为研究区有利区预测奠定一定的理论基础。

Accumulation mechanism of deep tight sandstone gas reservoir in Kelasu structural belt,Kuqa Depression

In order to better understand the accumulation mechanism of deep tight sandstone gas in Kelasu structural belt, a study was conducted on the history of hydrocarbon charging and porosity evolution. Taking the Dabei 1 gas reservoir in the Kuqa Depression as an example, the history of hydrocarbon charging was determined by fluid inclusion petrography and micro-temperature measurement technology, and the pore evolution history of the reservoir was restored by quantitative back-stripping method. The accumulation mechanism of Dabei1 gas reservoir was clarified according to the coupling relationship between them. The study results showed that there were three stages in hydrocarbon charging process in Dabei 1 gas reservoir. The first stage was the mature crude oil charging from Neogene Kangcun period to Kuqa period, forming a conventional reservoir, with the reservoir porosity from 12% to 14%. The second stage was highly mature hydrocarbon charging in Neogene Kuqa period, with the reservoir porosity from 8% and 10% and coexistence of conventional gas reservoir and deep-basin tight gas reservoir. The third stage was dry gas filling from Late Neogene Kuqa period to Quaternary western region period, forming tight conventional and deep-basin tight composite gas reservoirs, with reservoir porosity of about 5%. Since the western region period, a large number of fractures have been developed in the reservoir due to the late tectonic movement, and the gas reservoir has been relocated, that is, the natural gas migrated along the fractures under the action of buoyancy and accumulated in the high part of the structure. The study results further prove the prospects of tight gas exploration and development in the Kelasu structural belt in the Kuqa Depression, and provide a theoretical basis for the prediction of favorable areas in the study area.