Distribution and formation of tight oil in Qijia area, Songliao Basin, NE China

By using geologic, geochemical, well test, well drilling and well logging data, the formation conditions and distribution pattern of tight oil in Gao 3 and Gao 4 oil layers of Gaotaizi layer, Upper Cretaceous Qingshankou Formation, Qijia area, Songliao Basin were examined systematically. There are four favorable conditions for the formation of tight oil: high quality source rocks and reservoirs, good source and reservoir combination, and formation pressure. There are three series of source rocks in this area, K(2)qn(1), K(2)qn(2+3) and K(2)n(1), which provided material basis for the tight oil reservoirs; reservoirs including a variety of sands like distributaries channel, mouth bar and sheet sand are large in total thickness, wide in lateral distribution and good in continuity, providing accumulation space for tight oil; reservoir rocks of delta front in direct contact with the hydrocarbon source rock or pinching out in hydrocarbon source rock like fingers or interbedded with hydrocarbon source rock, constituted good source-reservoir combinations; abnormal overpressure in tight oil reservoirs with the pressure factor of 1.2-1.5, provided drive force for tight oil migration and charging. The study shows tight oil of Gao 3 and Gao 4 oil layers in Qijia area is mainly distributed in the center of, and slope and terrace around the sag.