低渗透储层应力敏感性与产能物性下限

采用CMS-200型孔隙度、渗透率测定仪,对采自大庆长垣东部榆树林、朝阳沟、头台等油田油层的16个岩芯样品进行实验,为了观察油田开发过程中低渗透储层的应力敏感性,选择了初始压力(原始地层压力)和最大围压(最大上覆岩压),并考虑油田注水开发的长期性及岩石本身的流变特性,在实验中适当延长了模拟压力恢复阶段的时间。实验结果表明,低渗透油田储层对应力的变化比较敏感,渗透率降低幅度较大。但随注水时间的延长,渗透率有不同程度的恢复,且恢复程度与渗透率大小有关:初始渗透率高,恢复程度大;初始渗透率低,恢复程度也低。特别是渗透率小于1.0×10^-3μm²的储层对应力的变化非常敏感,由此所产生的流固耦合现象也十分明显。因此可将渗透率小于1.0×10^-3μm²定为储层应力敏感性的界限。从油田开发角度来看,流固耦合作用的弊大于利,因此开采低渗透储层要尽可能保持地层压力开采,以清除流固耦合的影响。建议在制定储层产能界限时除考虑油层改造及开发技术进步的因素外,也必须考虑流固耦合作用的影响。经过综合分析,指出了大庆长垣东部油田储层的流固耦合作用的影响,并初步将本区的产能界限定为渗透率下限≥1.0×10^-3μm²,供油田开发决策参考。

STRESS SENSITIVITY AND POROPERM LOWER LIMIT OF DELIVERABILITY IN THE LOW-PERMEABILITY RESERVOIR

core samples collected from Yushulin,Chaoyanggou and Toutai oilfields to the east of Daqing placanticline have been tested with the CMS-200 porosity and permeability tester.For the sake of observing the stress sensitivity of low permeability reservoir during the oilfield exploitation, initial pressure (initial formation pressure) and maximum confining pressure (maximum overburden pressure)have been chosen;and the recovery time of simulated pressure have properly been prolonged,due to the consideration of the protracted nature of field's waterflood development and the rheological property of the rocks. Experimental results show that the low-permeability reservoir is relatively sensitive to stress change, i.e. the permeability will have a relatively large decrease with the increase of stress.However, permeability has also recovered to a certain degree with the waterflooding to be prolonged, and the degree of recovery is related to the extent of initial permeability: the degree of recovery is greater with higher initial permeability; vice versa. Especially the low-permeability reservoir with permeability of less than 1.0×10