The development characteristics of organic matter pores (OMPs) in shales is fundamental to the gas-bearing property of the shales. Detachment is one of the most common types of structural deformation in shale formations. To investigate the characteristics of OMPs in shear-deformed shale and the associated effects on the pore structure of shale gas reservoir, two sets of detachment zones and the intercalated non-detachment zone of shale formations in the Niutitang Formation of the Well XAD1 are studied. Based on scanning electron microscope observations and low-pressure gas adsorption tests, the impacts of shear on the shale pore structure are evaluated quantitively and the deformation mechanism for OMPs in shale is established.

Results indicate that the dominant pore type of shale in the Niutitang Formation of the Well XAD1 is OMPs. With the mineral rheology, organic matters are enriched in the clay gouge, which are more prone to shear deformation compared with those outside the gouge. Under shear, pores developed within the organic matter experienced directional elongation and compression, decreasing the pore sizes and lowering the volumes of the corresponding pores <30 nm; and the contact surface between organic matter and minerals becomes dislocated and open, increasing the volumes of the corresponding pores >30 nm. The effect of shear on OMPs is dominated by pore reduction. The volume loss ratio of shale micropores in detachment zones is the highest which can reach over 90%. The impact of shear on pore structures of non-detachment zone cannot be neglected within the thickness range of 5–20 m from the detachment surface, and the degree of pore reduction gradually decreases as the distance from the detachment zones increases. It is indicated that the detachment and its adjacent horizons are not favorable for shale gas exploration because of the low porosity and adsorption capacity.

页岩中有机质孔隙（OMPs）的发育特征是页岩含气性的基础。滑脱是页岩地层中最常见的构造变形类型之一。为研究剪切变形页岩中OMPs的特征及其对页岩气储层孔隙结构的影响，研究了XAD1井牛蹄塘组的两组滑脱带和夹层非滑脱带。基于扫描电镜观察和低压气体吸附试验，定量评价剪切对页岩孔隙结构的影响，建立页岩中OMPs的变形机制。

结果表明，XAD1井牛蹄塘组页岩的主要孔隙类型为OMPs。随矿物流变特性，粘土泥泥中有机质富集，较泥泥外更易发生剪切变形。在剪切作用下，有机质内发育的孔隙经历定向伸长和压缩，孔径减小，相应孔隙体积减小<30 nm；有机质与矿物的接触面错位开放，相应孔隙体积增大>30 nm。剪切对 OMP 的影响主要是孔隙减少。滑脱带页岩微孔体积损失率最高，可达90%以上。在距滑脱面 5～20 m 厚度范围内，剪切对非滑脱带孔隙结构的影响不容忽视，随着距滑脱带距离的增加，孔隙缩小程度逐渐减小。表明拆离层及其相邻层位孔隙度低，吸附能力低，不利于页岩气勘探。