Gas-bearing property evaluation by petrophysical logging in shale gas reservoirs: a case study in J area of Fuling shale gas field, Sichuan Basin

Abstract

The lithology of shale reservoirs is complex and the types of storage porosity are diverse. The existing gas-bearing property evaluation system by petrophysical logging is not perfect. In order to deepen the understanding of the gas-bearing capacity evaluation of shale reservoirs in J area of the Fuling shale gas field in the Sichuan Basin, the density-neutron curve superposition method, natural gamma-de-uranium gamma curve superposition method, and uranium-thorium ratio method are applied in qualitative recognition. Quantitative logging research was carried out on gas-bearing parameters such as adsorbed gas, free gas, porosity, and gas saturation. Based on the multi-parameter comparative study, organic carbon content, porosity, gas saturation, siliceous content, and burial depth are selected as the logging evaluation parameters that affect gas-bearing properties. A logging evaluation index (GQ) for gas-bearing capacity is constructed using fuzzy correlation analysis. The gas-bearing evaluation criterion is established, that is, GQ ≥ 0.57 for type Ⅰ gas-bearing reservoirs, 0.37 < GQ < 0.57 for type Ⅱ gas-bearing reservoirs, and GQ ≤ 0.37 for type Ⅲ gas-bearing reservoirs. The application of this method in J area shows that the accuracy of the quantitative prediction model for gas-bearing parameters is high, and the gas-bearing evaluation criteria can effectively evaluate and classify the gas-bearing properties of the reservoir.

Keywords

• gas-bearing property
• fuzzy correlation
• well logging evaluation
• wufeng-longmaxi formations
• fuling shale gas field
• sichuan basin