沾化凹陷仓储层的孔隙度和埋深对油气运聚的影响

Influence of porosity and burial depth on oil migration and accumulation in storage layer of Zhanhua depression

在不考虑幕式排烃的情况下,对沾化凹陷成藏期仓储层进行研究,揭示了仓储层的孔隙度和埋深与油气运聚间的关系。在对现今仓储层的厚度、物性和埋深等基本特征研究的基础上,通过对沉积埋藏史的分析,建立成藏期仓储层埋深及孔隙度的演化函数,恢复成藏期仓储层的古埋深和古孔隙度;利用公式计算出成藏期仓储层内油气运移所受的浮力及毛管压力,根据浮力与毛管压力的差值判断仓储层内油气的运聚状态,当差值为正时,说明运移的动力大于运移的阻力,仓储层以运移油气为主;当差值为负时,说明运移的动力小于运移的阻力,油气不能在仓储层中运移,表现为成毯或成藏的状态。利用动、阻力差值的分布规律,结合古孔隙度、古埋深的恢复结果,可对油气运移、成藏的孔隙度和埋深等要素进行界定。结果表明,沾化凹陷古仓储层油气运移的孔隙度下限为34.5%,埋深下限为1300m;现今仓储层油气运移的孔隙度下限为30.9%,埋深下限为1789m。

In order to reveal the connection between porosity and burial depth of storage layer and hydrocarbon migration-accumulation,the study of storage layer during pool-forming period in Zhanhua depression is developed without considering the episodic hydrocarbon expulsion.According to the study of basic characteristics of current storage layer,such as thickness,physical properties and burial depth,and by means of the analysis of depositional and burial history,the depth and porosity evolution function of storage layer is established to restore the paleoburial depth and paleoporosity of storage layer during pool-forming period,and the buoyancy force and capillary pressure that oil possessed could be calculated.The condition of storage layer can be categorized by difference between buoyancy force and capillary pressure,that is,the positive difference shows that oil in storage layer is primarily migrating,while the negative one shows that carpet-forming or pool-forming is the main condition.So,the function of current storage layer to hydrocarbon migration and accumulation can be revealed in the way of determining the present boundary,by which is deduced the porosity and depth boundary of oil migration and pool-forming in storage layer during pool-forming period.The threshold of porosity and depth are 34.5% and 1300 m respectively during pool-forming period,and the present are 30.9% and 1789 m.