Seismic Prediction of Carbonate Reef or Oolitic Reservoirs in Central Sichuan Basin

Abstract According to previous geological achievements, the development of the reef or oolitic reservoir is closely related to sedimentary facies. The reef or oolitic reservoir belongs to hidden lithologic trap, and the sedimentary evolution process and palaeogeomorphology settings of open sea platform-ocean trough sedimentary facies belt formed in the Late Permian in Sichuan basin are very complicated. As the platform continuously increased, ocean trough gradually disappeared in Feixianguan Period. Furthermore the physical properties of the reef or oolitic reservoirs have features of lithologic traps, such as strong heterogeneity and complex gas-water relationships which make it very difficult for seismic prediction. In recent years, we developed sedimentary facies prediction technique as well as seismic prediction technique series of carbonate reef or oolitic reservoir by tracking on seismic prediction techniques of carbonate reef or oolitic reservoir based on seismic facies. First, we made fine horizon correlation and sequence stratigraphy analysis, then simulated the multicycle sedimentary evolution process from the Feixianguan to Changxing period. After that, we applied the following techniques: forward modeling, layer flattening, ancient landscape restoration and seismic facies pattern. Finally we established different sedimentary facies belts and made seismic prediction. According to the analysis on the reservoir features of logging data, we established reservoir identification pattern which expressed low gamma and low acoustic impedance. Then we adopted facies-controlled inversion technology, carried out reservoir prediction in the favorable facies belts of reef and oolitic reservoir; finally made gas and water detection with such techniques as waveform decomposition and frequency alias attenuation and so on. The carbonate reef or oolitic reservoir prediction techniques have been widely applied and good drilling effects have been obtained. In central Sichuan, 40 exploratory wells have been deployed after using these techniques prediction results. Presently, 22 wells have been completed and among them 20 wells have drilled reef or oolitic reservoir. By using these techniques, the distribution of reef or oolitic reservoir was ascertained further in the two banks of Kaijiang-Liangping trough, and the west bank of western Hubei trough. And the hydrocarbon exploration fields in Sichuan Basin were widened.