湘西北常页1井下寒武统牛蹄塘组页岩气储层特征

摘要

The Changye No.1 well is an investigation well intersected thickest marine shale sector in the country at present, thickness of its lower Cambrian Niutitang Formation shale is about 700m. The shale assemblage is mainly silty shale, silty shale intercalated with mudstone, carbonaceous shale, marl, calcareous shale, carbon containing calcareous shale, aplitic limestone, and siliceous shale, see al⁃so calcareous concretions and pyrite bands. The bottom 200m part is mainly organic matter rich carbonaceous shale, its total quartz, feldspar and pyrite average amount is 41.9%, average clay minerals content 27.9%, average calcite, dolomite content 8.7%, similar to the typical American shale reservoirs. Organic carbon content in Niutitang Formation shale bottom part is 3.9%~17.6%, upper part 0.3%~2.1%; average porosity 1.57%, average permeability 0.004 × 10-3μm2. Under the argon ion polishing scanning electron micro⁃scope, the micropores in shale include mainly mineral intercrystalline (solution) pore, intercrystalline space, pore in crystal, micropore and microfissure in organic matter etc. Based on specific surface-pore size analysis, maximum shale pore throat median radius is 6.6nm, average 5.5nm. The study has shown that there is a certain relationship between Niutitang Formation marine shale gas storage capacity and pore volume, porosity, mineral composition, TOC etc., in which, organic carbon content is the dominating factor impacting shale gas content, followed by quartz, clay mineral, pyrite contents, specific surface and BJH total pore volume. Using the multiple lin⁃ear regression method, a Changye No.1 well Niutitang Formation shale gas content geological model has been set up.%湘西北常页1井为目前国内钻遇海相页岩层段厚度最大的调查井，其下寒武统牛蹄塘组页岩厚度约700m。该套页岩组合以粉砂质页岩、粉砂质页岩夹泥岩、炭质页岩、泥灰岩、钙质页岩、含炭钙质页岩、细晶灰岩、硅质页岩为主，见钙质结核及黄铁矿条带。其底部200m以富有机质炭质页岩为主，石英、长石和黄铁矿总量平均为41.9%，粘土矿物含量平均为27.9%，方解石和白云石含量平均为8.7%，与美国典型页岩储层相似。牛蹄塘组页岩有机碳含量底部为3.9%～17.6%，上部为0.3%～2.1%；平均孔隙度为1.57%，平均渗透率为0.004×10-3μm2。氩离子抛光扫描电镜下页岩微孔隙主要包括矿物晶间(溶)孔、晶间隙、晶内孔，有机质内微孔和微裂缝等。根据比表面-孔径分析，页岩孔喉中值半径最大为6.6nm，平均为5.5nm。综合研究认为牛蹄塘组海相页岩储气能力与孔隙体积、孔隙度、矿物成分、TOC等均有着一定的关系，其中有机碳含量是影响页岩含气量的最主要因素，其次是石英含量、粘土矿物含量、黄铁矿含量、比表面积和BJH总孔体积。利用多元线性回归法，建立了常页1井牛蹄塘组页岩含气量地质模型。