Tectonic Belt. Chuandong Northern Luojiazhai Feixianguan Group Reservoir Evaluation

The Feixianguan Formation in Luojiazhai Structure Zone of northeastern Sichuan Basin contains excellent oolitic-shoal reservoirs. However, many exploration and development difficulties still exist. In order to solve some of these problems,according to the principles of the structural geology, the high-resolution sequence stratigraphy , the sedimentary geology and petrology , three mian fields have been probed as follows: (1) the description of sedimentary facies around Luojiazhai Structure Zone, (2) the reservoir characterization of the dolomite oolitic shoals ,(3) the study of the spatial distribution, the main controls of reservoir-quality and the prediction of the dolomite oolitic formation.Firstly, based on the field outcrop, the description of 20 well cores , a lot of study achievements of the thin section petrography and field studies of sedimentary facies, the sedimentary facies of the Luojiazhai region has been probed, using the high-resolution sequence stratigraphy .According to data from field surveys, drilling, logging and other means, 3rd-order (Ⅲ₂ and Ⅲ₂) have been recognized within the Feixianguan Formation. Each 3rd-order sequence comprises TST and HST. The interface between Ⅲ₁ and Ⅲ₂ present as a drowned unconformable surface. Based on frequency spectrum analysis with Th/K as the main index, eleven 4th-order sequences have been outlined in the Feixianguan Formation. And the distribution of the sedimentary facies of the oolitic shoals formation in each high-frequency sequence has been outlined.Secondly, based on the characteristic of rock mechanics,reservoir space, reservoir physical property and pore structure the reservoir rock and pore structure of the Feixianguan Formation of the oolitic shoals have been subdivided into 4 types. Reservoir-quality evaluation of each every type of has been outlined, which contains reservoir physical property, production capacity, distribution of each reservoir rock types, and the type and distribution of reservoir space.Finally, the spatial distribution and the main controls of the reservoir-quality of the dolomite oolitic formation haves been evaluated .At the same time, the distribution of the oolitic dolomite has been predicted preliminarily. The reservoirs in Luojiazhai area are porous-type , and physical property in the eastern structure zone is better than the western. The favorable reservoirs consists of the ridge of larger oolitic shaol complexity or bars.