Logging Evaluation Method for Pore Pressure of Shale Gas Reservoirs-Taking Fuling Area, Sichuan Basin as an Example

Abstract

Unconventional oil and gas resources, especially shale gas resources have great potential for exploration and development in China. In Shale gas exploration and development process, reservoir pore pressure is a very important pa- rameter, and the pore pressure prediction can improve the appraisal accuracy of project dessert. This paper analyzes sev- eral formation pore pressure calculation methods based on logging data, and optimized the "Equivalent depth method". The preliminary results show that this method can carry out the accurate evaluation on the abnormal high pressure of the shale gas reservoirs of Fuling area with high calculation precision and application potential. Shale gas is natural gas extracted from shale, and mainly exists in the dark mud shale or high carbon mud shale. Shale has changeable mineral composition and complex pore struc- ture, therefore it mainly exists in surfaces of kerogen or clay particles in the adsorbed state, and exists in the cracks, pores and other storage space in the free-state, and also a very small amount of shale gas is present in dissolved state in kerogen or asphalt. The study area of this paper lies in the Fuling area of Sichuan basin, and its good potential of organ- ic rich shale mainly developed in the Longmaxi formation of Silurian to the Wufeng formation of Ordovician. The shale thickness is generally 40-210 m, the TOC content is from 1.0% to 5.0%, porosity ranges from 2% to 7.2%, and the buried depth is in the 2000 m to 3000 m range. The Longmaxi formation of Silurian is a set of black shale with gray green muddy siltstone. And the lithology of the Wufeng formation of Ordovician is gray dark silty mudstone that contain graptolite fossils.