低渗透油藏拟启动压力梯度

Pseudo threshold pressure gradient to flow for low permeability reservoirs

对大庆外围和长庆西峰油区低渗透油藏岩心进行了恒速压汞、核磁共振和渗流实验,从不同角度研究了低渗透储集层拟启动压力梯度形成原因及影响因素。由于储集层中固液作用形成的边界层的存在,且低渗透油藏喉道非常微细,因而低渗透油藏流体流动需要克服启动压力梯度。在低压力下,参与渗流的喉道少,岩心断面上的渗流截面小,随着驱动压力增加,参与渗流的喉道数量增加,岩心断面上的渗流截面增大。储集层的孔隙结构特征、可动流体饱和度对拟启动压力梯度有显著的影响,主流喉道半径及可动流体饱和度越大,拟启动压力梯度越小。拟启动压力梯度是储集层渗流非线性程度和渗流能力的表征参数,是孔隙结构、固液作用的综合体现。

Rate-controlled Hg injection experiments, NMR core tests and core flooding experiments are carried out to study the low permeability cores from the Daqing and Changqing oilfields. The forming and affecting factors are studied to demonstrate why the pseudo threshold pressure gradient to flow should be overcome. Because of the boundary layer caused by interaction between solid and fluid and the micro throats of low permeability reservoirs, the pseudo threshold pressure should be overcome for fluid to flow in low permeability reservoirs. Few throats are involved in the flow and the seepage cross section area is also less at lower pressures. The throats number and the seepage cross section area increase with the increasing of flooding pressure. The pore structure and movable fluid saturation of low permeability reservoirs have remarkable influence on the pseudo threshold pressure to flow, the bigger the mainstream throats and the movable fluid saturation, the less the pseudo threshold pressure to flow. The pseudo threshold pressure gradient to flow is a characteristic parameter of nonlinear flow degree and seepage ability and it is a synthetic symbol of pore structure and movable fluid saturation.