Marine Shale Gas Occurrence and Its Influencing Factors: A Case Study from the Wufeng-Longmaxi Formation, Northwestern Guizhou, China

Organic-rich shales were found in the Ordovician to Silurian Wufeng-Longmaxi Formation northwestern Guizhou province, China, which has high shale gas content revealed by field measurement. Shale occurrence, free gas/sorbed ratio, and their influencing factors are crucial for exploitation strategy. Results indicated that dominated type I kerogen, with total organic carbon (TOC) equivalent vitrinite reflectance (eqvRo) of 0.77%–6.98% 2.37%–2.53%, respectively. The porosity permeability range 1.23%–8.43% 3 × 10 − 4 – id="M2"> 2.23 1 mD, FE-SEM observation correlation analysis show is matter (OM) pores, followed interparticle (interP) pores related brittle minerals. CH4, derived from oil cracking, main component gas, but its proportion lower than Fuling Weiyuan areas, probably due weak preservation condition. Desorption lost determined situ desorption test 0.42–1.54 cm3/g 1.9–7.14 cm3/g, respectively, Langmuir volume ( id="M3"> V L ) isothermal adsorption experiment 1.63–4.78 cm3/g. positively correlated micropore volume, mesopore TOC negatively macropore clay mineral content, indicating methane preferentially stored micropores (<2 nm) mesopores (2–50 OMs. By comparing actual theoretical considered exist primarily sorbed state, can increase increased OM larger sizes also space gas. Combined two methods, it result accurate calculations reserves free/sorbed ratio. Based on this understanding, a model occurrence was proposed, provide reference normal pressure areas.