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The Largest Continuous Tight Gas Field in China: Characteristics and Evidences


Sulige giant gas field is the largest continuous tight gas field in China. This giant gas field is located in north-central Yishan Slope in Ordos Basin, with areas 30 thousand square kilometers, proven reserves over 2 trillion cubic meters, and yearly production over 10 billion cubic meters. The target strata of the field is in the Lower Permian tight sandstones, with the burial depth from 2500m to 4200m, per-well production 10-20 thousand cubic meters per day, and reserves abundance 120-150 million cubic meters per square kilometers. The giant field has five typical geological characteristics. (1) continuous distribution of gas reservoirs with large lateral extent in the downdip gentle slope; (2) widespread occurrence of superimposed tight-sandstone reservoirs with low/ultra-low permeability and micro pore-throats; (3)high maturity coal measures distributed in large dimensions; (4) tight sandstones with non-Darcy flow, indistinct gas-water contact, and non-uniform pressure system; (5) short-distance gas migration due to the limit of buoyancy drive. Evidences from geochemistry, reservoir Geology and paleo-tectonic background all verify that, the situation of natural gas distribution and accumulation present day in Sulige area is the result of the near-source migration-accumulation. Geochemistry evidence: Natural gas is mainly distributed in areas with higher gas-generating intensity, gas compositions don't suffer obvious processes of fractional distillation, gas-bearing saturation decreases away from the coal measures, and the isotopes of gas compositions is consistent with the source and maturity of the coal measures. Reservoir geological evidence: Intense compaction, quartz cementation and carbonate cementation led to the formation of the tight reservoirs before the main gas accumulation stage. Paleotectonic evidence: From the main gas accumulation stage to present-day, the paleo-tectonic slope kept in gentle, without formation conditions of higher vertical continuous gas column. The success of Sulige giant gas field, is of great importance for China's unconventional petroleum resources. It breakthroughs the traditional paradigm of trap exploration for conventional reservoirs, and extends new exploratory provinces to the whole basin. Further revolutions by theory innovation, technique progress and cost reduction, will promote these continuous tight reservoirs to be extensively exploited and to become actual commercial energies.