Gas-bearing influential factors and estimation of shale reservoirs in Upper Paleozoic, Ordos Basin

In the estimation of shale gas reservoirs, the shale gas content and the difficulty for fracture development are the main influencing factors. Six critical factors were chosen, including organic carbon content, the amount of adsorbed gas, maturity, porosity, and the content of I/S and brittle mineral. According to the theory of grey correlation grade, the shale reservoirs in the Upper Paleozoic in the Ordos Basin were studied. The reservoirs were classified into three types based on the Reservoir Estimating Index (REI). When REI≥0.5, the reservoirs belong to type Ⅰ. When 0.33≤REI<0.5, the reservoirs belong to type Ⅱ. When 0.3≤REI<0.33, the reservoirs belong to type Ⅲ. Combined with previous studies, an estimation scheme of transitional facies shale gas reservoirs in the study area was proposed, and the characteristics of different reservoirs were shown with images.