Palaeogeomorphology Restoration And Seismic Prediction Of Beach Reservoirs Of Maokou Formation, Western Sichuan Basin

Petroleum reservoirs of beach facies have the characteristic of good reservoir property, high richness of organic matter, good capability, high productivity, etc. So they have a vast exploration potential of oil and gas. But with the deepening of the exploration, carbonate beach facies reservoirs exploration focus from structural reservoirs to Lithologic- tectonics composite trap reservoirs which consist of beach facies or karst reservoirs with the local structural superimposed, at the same time, it may develops a separate beach body of lithologic trap reservoirs. This study is according the difficulties of beach facies reservoirs, the geological characteristics, logging responses and seismic responses of beach facies of reservoirs to restore palaeo-geomorphology and predict the beach reservoirs in Maokou formation of J- G area, and then forming an effective forecasting system of beach facies reservoirs that is “occupying beach facies, choosing geomorphology, finding fracture-cavity, overlaying tectonics”. At first, this paper detailed introduces the definition of beach, the difference between the reef and mound, the classification of them, then summary the characteristics of sedimentary facies and seismic facies of beach facies. Secondly, through the overview of the research region, structural history and sedimentary model,the paper is analyzed lithology characteristics, logging response characteristics and seismic response characteristics of Maokou formation in study area, then demarcating the seismic horizon and drawing construction of Maokou formation. Thirdly, we put forward the technologies of paleo-geomorphology restoration, using the impression method and the geophysical method, combining with the forward modeling in geomorphology and sedimentary characteristics to restore Maokou formation. Results indicate that, according to the strata thickness distribution of the Maokou formation, we can divide the formation of three geomorphic units covering karst highland, karst slope, karst depressions. Which is advantageous zone to develop high-energy beach is karst slope that has the smaller travel-time and stronger amplitude. Fourthly, combining the sensitivity analysis of lithology and logging and the characteristics geophysical response of beach reservoirs,using the Probabilistic Neural Network(PNN) to build a nonlinear mapping relationship between logging curve with seismic attributes in EMERGE module of Geoview, then it can realize the seismic inversion of gamma parameters,so as to quantitatively predicting the thickness distribution of reservoirs.Fifthly, using a variety of seismic attributes such as coherent properties,RS properties,curvature properties predict the crevice distribution, and then determining the development zone of fracture-cavity. Finally through frequency attenuation technique to identify the water or gas in the beach facies reservoirs, but the prediction is not well for result exist multiple solution. Ultimately through overlaying tectonics of the Maokou formation, combining with the feature of beach facies,the distribution of paleo-geomorphology and reservoirs, the development of fracture-cavity, we have a comprehensive evaluation of beach facies reservoirs, then optimizing the favorable exploration targets.To sum up, using the above methods can effectively predict the reservoirs distribution of beach facies, identify the high-energy beach facies favorable distribution area. All of them are provided theoretical support for drilling deployed of Maokou formation in this research area, affording important basis for the next step of oil and gas exploration.