| The deep Permian Copacabana carbonate formation is an important exploration interval in the Madre de Dios Basin in South America. The good gas test results and the discovering of commercial gas in Block 58 of Peru and its
surrounding areas，reveal good prospects for exploration. Due to the complex depositional environment of carbonate rocks and the unclear distribution of reservoirs, the exploration of this formation is restricted. Based on the analysis of
regional sedimentary environment and paleogeomorphology, combined with core description, thin section identification, well logging and seismic data analysis, the sedimentary characteristics and main controlling factors of Copacabana Formation were studied. It is shown that: (1) Copacabana Formation belongs to carbonate platform deposits, which can be divided into three sedimentary facies: open platform, limited platform and evaporation platform, and five subfacies: granular shoal, inter-shoal sea, lagoon, sandy debris shoal and tidal flat. (2) The granular shoal of open platform is widely developed in the lower part of the formation; the inter-shoal sea in the middle part of the formation extend from the southwest to the large area of the work area; the open platform inter-shoal-open platform granular shoal-restricted platform lagoon are developed from southwest to northeast in the upper part of the formation，and the regional weathering
crust is developed at the top. The sedimentary sequence of retrogradation-aggradation-progradation is displayed from bottom to top. (3) Reservoir development is controlled by the dual effects of paleogeomorphology and sea level rising and falling: the height of paleogeomorphology leads to different weathering degrees，which further controls the development of weathered crust, sandy dolomite and dolomitic limestone reservoirs; the periodic change of sea level causes the migration of granular shoal，which then controls the development of granular limestone reservoirs. According to the above understandings, it is clear that the weathering degree is limited, the open platform granular shoal is mainly developed, and the grainstone is the main reservoir type in the study area. This research initially evaluate the potential of carbonate reservoirs of the study area, and is instructive for carbonate oil and gas exploration. |
