构造裂缝对致密砂岩气成藏过程的控制作用

The Controlling of Structure Fractures on the Accumulation of Tight Sand Gas Reservoirs

塔里木盆地库车坳陷致密储层中构造裂缝普遍发育,裂缝的形成与分布对致密砂岩气成藏过程具有重要的控制作用。结合前人的研究成果,利用岩心、测井等资料分析库车坳陷依南地区构造裂缝形成时间、发育位置及发育强度,认为构造裂缝形成时间晚于依南2致密砂岩气藏形成时间,裂缝既发育在气藏内部,也发育在气藏的边界,裂缝发育程度具有不均一性。综合分析裂缝时空分布规律以及发育强度,认为致密储层中发育的裂缝对致密砂岩气藏的控制作用主要表现在:①裂缝形成以后,天然气运聚动力发生改变,天然气在裂缝内以浮力为主要的运聚动力,在基础孔隙中则以分子膨胀力为主要的运聚动力;②当裂缝晚期发育,且发育在气藏内部时,裂缝改善了致密储层的物性条件,形成了有利于天然气运聚成藏的优势通道及储集空间;③当裂缝晚期发育,且发育在原型致密砂岩气藏边界时,原型致密砂岩气藏遭到破坏,气藏发生萎缩。

Tectonic fractures developed widely in the tight-sand reservoir in Kuqa Depression,Tarim Basin. The formation and distribution of these fractures exerted great impact on the tight sand gas reservoirs. Based on the analyses about the formation time, distribution and intensity of fractures with the core and logging data in Ahe Formation of Yinan 2 reservoirs,this paper holds that the fractures were developed in tight sand reservoirs later than the time that Yinan 2 gas reservoirs formed,and they spread both in the in- ternal and boundary of the reservoirs with different intensity. As a result, the impact of fractures developed in the tight sand reservoir on the tight sand gas reservoirs are as follows： （1）After the formation of frac- tures,the accumulation dynamics were changed. Buoyancy was the main dynamic for natural gas to move in the fractures,while the molecular swelling force was the chief one in the basic porosities. （2）When frac- tures developed later than the gas reservoir and occurred within the reservoir, fractures improved the prop- erty of tight reservoir,acting as main migration pathway as well as storage space. （3）When fractures devel- oped later than the gas reservoir and occurred on the boundary of the original tight-sand gas reservoirs, fractures can change the critical condition of tight sand gas reservoirs, resulting in the destruction and shrinkage of reservoirs.