基于压力衰减法的页岩气体扩散系数应力敏感性实验  

Stress sensitivity experiments of shale gas diffusion coefficients based on the pressure decay method

作　　者：康毅力[1] 赖哲涵 陈明君[1] 侯腾飞 游利军[1] 白佳佳 余中慧 KANG Yili;LAI Zhehan;CHEN Mingjun;HOU Tengfei;YOU Lijun;BAI Jiajia;YU Zhonghui(State Key Laboratory of Oil&Gas Reservoir Geology and Exploitation//Southwest Petroleum University,Chengdu,Sichuan 610500,China;CNPC Engineering Technology R&D Co.,Ltd.,Beijing 102206,China)

机构地区：[1]“油气藏地质及开发工程”国家重点实验室·西南石油大学 [2]中国石油集团工程技术研究院有限公司

出　　处：《天然气工业》2022年第2期59-70,共12页Natural Gas Industry

基　　金：国家自然科学基金“临界解吸压力约束下的常压页岩气多尺度输运机理研究”(编号:41902154);西南石油大学开放实验基金“富有机质岩石超临界水增渗实验研究”(编号:2020KSZ01024)。

摘　　要：页岩气衰竭式开采过程中储层有效应力逐渐增大,且气体产出是跨越解吸、扩散和渗流的多尺度传质行为,其中扩散是沟通解吸和渗流的桥梁,但以往研究尚未对气体扩散能力的有效应力响应特征给予足够重视。为此,选用四川盆地南部地区(以下简称川南地区)志留系龙马溪组页岩样品,设计并开展了不同有效应力下的压力衰减实验,揭示有效应力变化对气体扩散能力的响应机制,提出页岩基块应力敏感指数(IS_(SGD)),以定量表征基于气体扩散能力的页岩基块应力敏感性。研究结果表明:①气体扩散量随有效应力增加而降低,且变化前期快、后期慢;②随有效应力增加,大于50 nm孔缝气体扩散时间缩短;③基块岩样IS_(SGD)为25.68%,应力敏感程度为中等偏弱,而裂缝岩样则表现出更强的应力敏感性。结论认为,随着有效应力增加,页岩基质孔隙中扩散系数降低,但微裂缝中原先以黏性流、滑脱流为主的流动通道被压缩,气体流动方式逐渐以扩散为主,气体扩散系数增大,但总体输运能力仍明显降低,因此推荐川南地区页岩储层有效应力维持在17~30 MPa,有助于基块向裂缝稳定供气。During the depletion exploitation of shale gas,the effective stress of reservoir increases gradually,and the gas production is a multi-scale mass transfer behavior including desorption,diffusion and seepage,among which diffusion is the bridge between desorption and seepage.In the previous studies,however,less attention is paid to the response behaviors of gas diffusion capacity to effective stress.Taking the shale samples of Silurian Longmaxi Formation in the southern Sichuan Basin as the research object,this paper designs and carries out gas pressure attenuation experiments under different effective stresses.In addition,the response mechanism of shale gas diffusion capacity to effective stress is analyzed,and the stress sensitivity index(IS_(SGD))of shale matrix is proposed to quantitatively characterize the stress sensitivity of shale matrix based on gas diffusion capacity.And the following research results are obtained.First,the gas diffusion rate decreases with the increase of effective stress,and its variation is fast in the early stage and slow in the late stage.Second,with the increase of effective stress,the diffusion time of gas in pores larger than 50 nm becomes shorter.Third,the IS_(SGD) of the matrix sample is 25.68%,and its stress sensitivity is moderate to weak,while the fractured rock sample shows stronger stress sensitivity.In conclusion,with the increase of effective stress,the diffusion coefficient in the pores of shale matrix decreases,but the flow channels previously dominated by viscous flow and slippage flow in micro fractures are compressed,the gas flow pattern gradually transforms into diffusion,and the gas diffusion coefficient increases.However,the total gas transport capacity is still reduced significantly.Therefore,it is recommended to maintain the effective stress of the shale reservoir in the southern Sichuan Basin at 17-30 MPa,which is conducive to the stable gas supply to hydraulic fractures from the matrix.

关 键 词：页岩气 志留系龙马溪组 应力敏感 扩散 压力衰减 多尺度 孔隙结构 

分 类 号：P618.13[天文地球—矿床学]