四川盆地长宁龙马溪组页岩赋存空间及含气规律

四川盆地长宁地区下志留统龙马溪组页岩广泛发育，该地区页岩储层的微观孔隙结构及全尺度孔径分布特征尚不明确，运用聚焦离子束扫描电镜、高压压汞、低温氮吸附及低温CO₂吸附等实验技术，以宁203井为例，研究了龙马溪组下部页岩储层的孔隙结构特征，并建立了一套页岩纳—微米全尺度孔径分布测试分析方法。该方法利用气体吸附法和高压压汞法获得第1孔径分布数据和第2孔径分布数据，通过对2种方法获得的重复部分孔径分布数据进行差异性分析，并根据分析判断结果获取处理后的孔径为3.7～200.0 nm的分布数据，再结合2种方法获得的不重复部分的孔径分布数据，从而可以计算微孔、介孔和宏孔在整个岩石样品中的占比，获得岩石样品全尺度孔径分布数据。结果表明：该区龙马溪组下部页岩孔隙结构复杂，“墨水瓶”状细颈孔隙大量存在，微孔与中孔、大孔相互连通，但孔喉细小，连通性较差；介孔和微孔占比超过80%。直径> 15 nm的孔喉中主要为游离气，直径< 2 nm的孔喉中主要为吸附气。

Storage space and gas content law of Longmaxi shale in Changning area,Sichuan Basin

The shales of the lower Silurian Longmaxi are widely developed in Changning area of Sichuan Basin. The micro pore structure and full-scale pore size distribution characteristics of shale reservoirs in this area are not yet clear. The pore structure of lower Longmaxi shale reservoir was researched by field emission scanning electron microscope(FE-SEM),high pressure mercury intrusion,low temperature nitrogen adsorption and low temperature CO₂adsorption. Taking the Ning 203 well as an example,a set of analysis method about nanometer-micrometer full scale pore size distribution was established. The first pore size distribution was obtained by gas adsorption, and the second pore size distribution was obtained by high pressure mercury intrusion in this method. The difference between the data of the pore size distribution obtained by the two kinds of tests was judged. According to the result of the judgment,the pore size distribution data of 3.7-200.0 nm were obtained after treatment. The pore size distribution data of the non-repeated pore size were obtained by the two methods combined. The micropores,mesopores and macropores for core samples in proportion were calculated,so the full-scale pore size distribution data of core samples were obtained. Results show the lower part of Longmaxi shale pore structure is very complex. Micropores are connected in series with mesopores and macropores. The pore throat is small,so the connectivity is poor. Mesoporous and microporous accounted for the percentage of pore volume is more than 80%. Pore throats of the diameter above 15 nm mainly contain free gas,and the ones below 2 nm mainly contain adsorbed gas.