页岩气储层非均质性研究——以四川盆地下寒武统筇竹寺组为例

RESEARCH OF SHALE GAS RESERVOIR HETEROGENEITY:A CASE OF THE LOWER CAMBRIAN QIONGZHUSI FORMATION OF THE SICHUAN BASIN

在详细调研国内外页岩气储层非均质性研究的基础上,以四川盆地下寒武统筇竹寺组为例,通过平面、层内和微观3个方面分析了泥页岩非均质性特征。平面非均质性主要受区域沉积特征和泥页岩有机地球化学特征控制,盆地中西部主要发育泥质砂岩和砂质泥岩,总有机碳含量TOC和有机质成熟度相对较低;东北部泥质灰岩发育,TOC和有机质成熟度较高;南部以碳质泥页岩为主,TOC和有机质成熟度最高(镜质体反射率Ro可达4.0%)。连井剖面和单井泥岩层矿物特征分析表明,层内非均质性较强,主要表现为横向上地层总厚度、泥页岩单层厚度、泥页岩发育层数、夹层特征和顶—底板岩性沿剖面变化快,纵向上矿物成分和岩石脆性度差异明显。微观非均质性主要受孔隙类型和基质微裂缝影响,黏土层间孔隙和有机质孔隙发育,基质微裂缝对沟通孔隙起主要作用。综合分析认为,四川盆地下寒武统筇竹寺组页岩气储层非均质性特征明显,对页岩气井产能和页岩气采收率有重要影响。

Along with the development of shale gas in favorable areas in China, the research of shale gas reservoir heterogeneity has become the key to improving shale gas recovery. Based on the detailed investigation of research programs on shale gas reservoir heterogeneity at home and abroad, taking the Lower Cambrian Qiongzhusi Formation in Sichuan Basin as a case, we studied the shale gas reservoir heterogeneity in three aspects： plane heterogeneity, interlayer heterogeneity and micro-anisotropy. The plane heterogeneity is mainly affected by regional depositional framework and organic geochemis- try. The western part of the basin is dominated by argillaceous sandstone and sandy mudstone with low organic matter and low maturity, while the northeastern part of the basin dominated by argilla- ceous limestone with high organic matter and high maturity. The southern part of the basin, howev- er, is dominated by carbonaceous mudstone with rich organic matter and highest maturity. The vit- rinite reflectance Ro can reach 4 ~. Well correlation and mineralogy of a single mudstone layer shows that the reservoir interlayer heterogeneity is strong, the total thickness of the Formation, thickness of single shale layer,number of shale layers and intercalations vary strongly in lateral direction. The li- thology of the roof and floor changes quickly along the horizontal section,and the mineral composition and rock brittleness change quickly along the vertical profile. The micro-heterogeneity is mainly af- fected by the pore types and matrix microcracks. The clay interlayer porosity and organic matter po- rosity are well developed. Matrix microcracks play an important role in pore connection. Through the comprehensive analysis of the Lower Cambrian Qiongzhusi Formation,it is concluded that the hetero- geneity characteristics of a shale gas reservoir renders important effect on shale gas productivity and recovery rate.