Eastern Chongqing Permian System Of Reef And Oil And Gas Research

Reefs or bioherms are an impotant type of carbonate deposits. They are consist of numerous and all kinds of organisms, or resulted from biological action. Reefs are also a valuable sedimental type containing oil and gas, and in recent years geologists have paid more attention to them. Many oil and gas pools accumulated in the reefs have been found in the domestic and abroad districts, which contributed considerably to the global source supply.Permian is an important period in the development of reef and reef-building organism in the world. Reefs are well developed in western Hubei and eastern Chongqing. Through sedulous research, the whole acquaintance on types of reef builders, types of reef carbonatite, development and evolution of reef organisms, division of reef facies, distributing regularities of reefs and diagenesis has been concluded. According to the comprehensive studies, the following results and conclusions have been obtained.1. The reefs are mainly distributed in the margin and the inner of the Upper Permian Changxing platform. And the reefs can be divided into three types: reefs developed in the margin of platform, mud mound in the low slope and patch reefs within the platform. The reefs with linear appearances stretching from south to north in Jiantianba-Linchang are margin reefs, reefs located in the low slope of Hongchun gulf are mud mound, and reefs in Jiang 7 well, Shibaozai and Laolongdong etc. are patch reefs.2. Frame-building organisms mostly are Sphinctozoa, Inozoa, Hydrozoa, Tabulozoa. Binding organisms mainly are Bluegreen Algae, Tubiphytes and Tabulozoa. Accessory organisms are bryozoa, brachiopoda, foraminifera, echinodermata, etc. what's more, biota are different with various reef facies.3. The formation and distribution are vulnerable to regional topography which is related to faults. In studied areas, reefs of western areas grew bigger in dimensions than those of the eastern, and the strata in whichcaning reefs became upper. These characteristics have close relation with transgression from eastern to western.4. Reefs undermined various and complicated diagenesis, in which cementation, dolomitization and corrosion etc. play main roles in the history of reef diagenesis. The great number of pores of reef rocks disappeared due to multi-generational cementation in submarine and taphonomic environments. The pores in reef rocks are mainly secondary and the primary pores are almost filled up. The evolution of pores is wholly controlled by diagenesis, all in a word, the histoty of diagenesis is evolution of pores.5. Platform trough and basin with deep water and low energy are the favorable source rock zones, reef banks and reef cores are the profitable reservoir. And the strata which is dolomitized is the main gas yielding parts.