Sulige field in the Ordos Basin: Geological setting, field discovery and tight gas reservoirs

The Sulige gas field in central Ordos Basin is one of the largest gas fields in China, with about 860.7 billion cubic meters (bcm) of proven gas reserve. This field covers an area of about 500 km2, with largely tight clastic reservoirs. The Upper Carboniferous–Lower Permian deltaic sandstones and Upper Permian lacustrine mudstones deposited in a stable cratonic tectonic setting form an effective petroleum system that is favorable for gas accumulation in large-scale stratigraphic–lithologic traps. Based on wire line log response, drilling stem test and core data, a generalized classification system was developed for the gas reservoirs of the Sulige field, thus Type I and II rocks are capable of gas production without natural and/or artificial fracturing, Type III rocks are capable of gas production after artificial fracturing and Type IV rocks are too tight to produce at commercial rates even with artificial fracturing. The discovery of the Sulige field not only adds large gas reserve in the Ordos Basin, but strongly indicates the overlook potential of both tight sandstone reservoir rock and relatively porous and permeable sweet spots in it.