Reservoir characteristics and gas-bearing capacity of the Wufeng-Longmaxi Formation in the Well Eyy2, east Huangling Uplift, western Hubei Province

The organic-rich shale of the Wufeng-Longmaxi Formation in the western Hubei Province has become a hotspot for the shale-gas exploration in South China. In order to deepen the understanding of reservoir characteristics and gas-bearing capacity, the lithological and geochemical characteristics, types and features of reservoir space, and gas-bearing capacity were detailedly studied on the basis of the drilling and testing data of the Well Eyy2, as well as the affecting factors of shale gas and evaluation of shale reservoir. The results show that the organic-rich shale extending to LM7 graptolite zone in the Well Eyy2 is about 16m in thickness and the LM5-LM6 graptolite zone is missing, which is mainly composed of siliceous shale interbedded with silicastone, mixed shale and clay shale. Organic type is type Ⅰ and Ⅱ₁, with Ro value ranging from 1.88% to 2.03% indicating that the shale is under massive gas generating stage. The main reservoir space consist of organic nanopores with diameter less than 100 nm, micropores with diameter exceed 5um and tectonic microfracture, of which the volume ratio of nanopore is more than 50%. Pore volume and specific area has closely positive relationship with total organic content (TOC). The on-site measured core gas content ranges from 0.068 to 3.33 m³/t with average of 1.13 m³/t, and the graptolite zone WF2-WF3 in the Katian and LM2-LM4 in the Rhuddanian has highest gas content. Gas content has obviously positive correlation with TOC and brittle mineral content. According to the TOC, gas content, brittle mineral content, shale sedimentary environment and other parameters, the favorable reservoir (typeⅠ) with about 9 m in thickness mainly corresponds to siliceous shale interbedded with silicastone of the graptolite zone WF2-WF3 in the Katian and LM2-LM4 in the Rhuddanian formed in the deep-water sedimentary environment, which is the best "sweet spot" for the horizontal drilling in the shale gas exploration in the Wufeng-Longmaxi Formation.