渤海湾盆地歧口凹陷古近系沙三段页岩油储层非线性渗流特征

Nonlinear seepage characteristics of shale oil reservoirs of the third member of Paleogene Shahejie Formation in Qikou Sag,Bohai Bay Basin

通过高压压汞与低温气体吸附实验,结合核磁共振在线检测系统和驱替实验,对渤海湾盆地歧口凹陷古近系沙三段页岩油储层的渗流特征进行了研究。研究结果表明:①歧口凹陷古近系沙三段3种岩相页岩的微孔数量占比最大。与块状泥岩相比,纹层状及层状页岩储层的孔径大于100 nm的中大孔喉更为发育,储集性及渗流能力更优。②赋存在页岩储层大孔喉中的可流动油能有效产出,但由于渗流阻力较大,微小孔喉(小于100 nm)中的油即使在很大压差下也难以产出。③页岩储层中的石油渗流具有启动压力梯度和非线性渗流的特征,但不同岩相的渗透特征差异较大,其中纹层状页岩拟启动压力梯度最小,渗流能力最强,层状页岩储层具有一定的渗流能力,块状页岩储层渗流能力最差。在相同压力梯度下,块状页岩中的流量仅为纹层状页岩中流量的10%左右,基本无自然产能。

Through high-pressure mercury injection and low-temperature gas adsorption experiments,combined with nuclear magnetic resonance online detection system and displacement experiment,the seepage characteristics of shale oil reservoirs of the third member of Paleogene Shahejie Formation(Es3)in Qikou Sag,Bohai Bay Basin were studied.The results show that:(1)The micropores of the three lithofacies shales of the third member of Paleogene Shehejie Formation in Qikou Sag account for the largest proportion.Compared with massive mudstone,the medium and large pore throats with pore diameter greater than 100 nm in laminated and layered shale reservoirs are more developed,and the reservoir properties and seepage capacity are better.(2)The flowable oil that occurs in the large pore throats of shale reservoirs can be output effectively,but the oil in the small pore throats(less than 100 nm)is difficult to output even under a large pressure difference due to the large seepage resistance.(3)The seepage of shale oil in shale reservoir has the characteristics of start-up pressure gradient and nonlinear seepage,but there are great differences among different lithofacies.The laminated shale reservoir has the lowest pseudo start-up pressure gradient and the strongest seepage capacity,the layered shale reservoir has a certain seepage capacity,while the massive shale reservoir has the poorest seepage capacity.Under the same pressure gradient,the flow rate in the massive shale is only about 10% of that in laminated shale,and there is no natural productivity.