The Karst Reservoir Characteristic And Seismic Prediction To The Ordovician Stratum On The Leshan-Longnvsi Paleouplift

Directed by the theory of Stratigraphy, Sedimentology, Reservoir Geology and the technology of seismic reservoir prediction, the Ordovician formation of Leshan-Longnvsi paleo-uplift is studied, which includes the sedimentary and reservoir characteristic, the form and control causation of the reservoir, paleo-geomorphy recovery, fissure prediction and seismic landscape forecasting to the reservoir. Study shows that the Ordovician carbonate formation in this area has the characteristic of very low groundmass porosity. The construction research indicates that it is a huge northeast leaned nose shape uplift below the Permian formation, it is a north leaned brae from the Permian to the Middle Triassic formation, and it is a smoothout construction consist of several folds from the Upper Triassic to the Jurassic formation. The top surface of the Ordovician carbonate strata is always high in the west and low in the east, and the An8 well area is in the high position of the study are all the times in the career of construction evolvement. The paleo-geomorphy before the sedimentary of the Permian formation is recovered with the Moulage method, then the karst geomorphy unit is partitioned. The recovered paleo-geomorphy shows that the undation of the ancient surface relief is not very acute, it is high in the west part of the study area and low in the east, and the gap between the highest and the lowest area is about 130 meter. Combined with the causes of lithology, stratum construction, geology structure, paleo-water system and paleo-geomorphy, the favorable areas for karst development are predicted out, which are in the carbonate basset region of the lower Ordovician formation and the middle area of Middle Ordovician formation basset region. Because of the strong anisotropic property of karst development, the techniques of wave impedance inversion, seismic attributes extraction, the coherence analysis, fissure prediction are adopted to predict the favorable region for the development of kasrt reservoir. The time window glide method of average wavelet extract and phase circumgyrate coherence analysis method of wavelet phase calculation are studied to make synthetic seismogram for horizon's fine calibration. And the feasibility study indicates that the cave or fissure can be recognized with general 2D seismic data. The fissure prediction was carried out with the main curvature method, and the favorable regions for fissure development are mainly distributed in the northeast and middle-north of the study area, and the stress orientated mainly to the northwest and northeast. The interest region for oil and gas exploration to the Ordovician formation are predicted combined the geology and seismic method's prediction result.