Water and gas distribution and its controlling factors of large scale tight sand gas fields: A case study of western Sulige gas field, Ordos Basin, NW China

The chemical characteristics and occurrence state of formation water in western Sulige gas field were analyzed based on geological features of reservoirs, the gas and water distribution regularity and the main controlling factors were determined. Aquifer zones are widely distributed in the whole Western Sulige gas field, gas zones developed poorly and distributed limitedly. Vertically, gas and water zones are of poor continuity and distributed in an isolated and staggered pattern. Inside the gas reservoir, there is not a uniform gas and water interface because of the hard differentiation between gas and water. On the whole, the lower segment of H8 Member in Shihezi Formation and S1 Member in Shanxi Formation are both better than the upper segment of H8 Member. Gas and water distribution of Western Sulige gas field is mainly controlled by gas-generating intensity, the distances between reservoirs and hydrocarbon source rocks, configuration relationship of sand shale and physical property differences inside sand body complex. Among them, gas-generating intensity mainly controls the macro pattern of gas and water distribution, with the decrease of gas-generating intensity, good gas accumulation gradually changes to be water associated gas reservoir. The closer the distance between reservoirs and hydrocarbon source rocks, the more developed the gas zones, on the contrary, the gas-bearing water zone and coexisting gas and water zone are more developed. Sand shale configuration relationship and physical property differences inside sand body complex mainly control the local gas filling and accumulation. Five types of gas and water distribution patterns are summarized: pure gas, thick reservoir with mixed gas and water, water above the gas, gas above the water, and gas sandwiched between water.