A Study On Carbonate Sequence Stratigraphy In Block X Of Pre-Caspian Basin

The carbonate reservoir beds play a very important role in the world petroleum exploration discoveries, and the prediction of such reservoir beds has troubled oil industry for many years. In this paper, by studying carbonate sequence stratigraphy in Block X of the Pre-Caspian Basin, we confirmed the characteristics of the carbonate sedimentary facies and development regularity of carbonate reservoir beds in this study area, which effectively guided its future exploration directions.The Pre-Caspian Basin is one of the petroliferous basins with the biggest subsidence in the world. This basin has very thick salt domes, and its main oil and gas bearing formations are the sub-salt carbonate reservoir beds. In this paper, we utilized carbonate sequence stratigraphy, analyzed the deposit background of the whole basin, correlated sequence stratigraphy in single well, cross-wells and seismic sections by well-seismic combination, confirmed the features of 3rd and 4th orders of stratigraphy boundaries in this study area, conducted fine seismic interpretation, and set up sequence stratigraphy framework of this area. After that, by rock thin sections, cutting loggings and well logging curves, through analysis of formation thickness, seismic facies and seismic attributes, combining carbonate deposit patterns, we established the sedimentary facies marks of different sedimentary bodies of the 4th order sequences. We identified four types of sedimentary subfacies(platform evaporates, restricted platform, open platform and shelf), ten types of sedimentary microfacies(gypsum rock, lagoon, local beach, etc.), and confirmed the favorable sedimentary facies belts(platform margin beach, local beach and dolomite flat). We analyzed the controlling factors for sedimentary facies evolution: the relative changes of sea level controlled the development characteristics of each sequence, and the frequent oscillation of sea level led to many drowned unconformities and migration of these sequences in this area. On the basis of confirming the favorable sedimentary facies belts, we selected favorable target zones to do facies-controlled multi parameter seismic inversion and reservoir prediction, and proposed favorable directions for future exploration.