Prediction of Carbonate Depisitional Microfacies Using Image Logs

Abstract

Summary Carbonate rocks typically have complex and heterogeneous microscopic pore structures and macroscopic performances. However, it’s difficult to predict the microfacies in a single well due to the limited core data. The high-resolution borehole image logs (FMI) could provide continuous digital records of reservoir rocks with information about lithology, depositional textures, and sedimentary sequences, and therefore can be used for the detailed interpretation of sedimentary facies. The Majiagou Formation, which consists of dolomite, limestone, and evaporate, is important gas-bearing stratigraphic units in Ordos basin. The pore systems include intercrystalline pores, intercrystalline dissolution pores, moldic pores , and intergranular dissolution pores. The sedimentary environment of the Ordovician dolomite in the study area is restricted platform in which the gypsum-bearing dolomite flat, dolomitic flat and grain bank are favourable for high-qualigy reservoir development. The most important reservoir is dolomite reservoir, and the main pore space is intercrystalline pore, dissolved intercrystalline pore, dissolved pore and micro-fracture. By the contrast of image and conventional logging characteristics of the above depostional microfacies, we summarize the relationship between carbonate platform facies and image logs, and predict the depositional microfacies using a combination of conventional and image logs.