Characterization of Lower Paleozoic Water and Gas Distribution in Yan’an Gas Field, Ordos Basin

Abstract

The distribution of gas and water in the tight gas reservoirs is complex. This limits exploration and development compared to conventional resources. Elucidating the characteristics that control fluid distribution is critical to unlocking the tight gas potential. This study combines geologic analysis with production data to reveal the water chemistry, gas−water distribution, and factors controlling zoning in the study area. The results show that (a) extracted water includes formation brines, condensate, and residual drilling fluids; (b) formation water dominates production, and the salinity of Lower Paleozoic brines is as high as 169,689 mg/ L; (c) low NaCl and high metamorphic coefficients indicate that the water bodies are disconnected and the hydrocarbons are wellpreserved in several gas−water systems; and (d) paleomorphological features, tectonics, and lithologies control the distribution of gas water. Discrete water bodies are widely distributed.