Dolomite geochemistry of the Cambrian Longwangmiao Formation, eastern Sichuan Basin: Implication for dolomitization and reservoir prediction

Abstract

Based on petrology and mineralogy, the geochemical characteristics of dolomite in the Cambrian Longwangmiao Formation in the eastern Sichuan Basin, were carried out. Results showed that dolomites mainly occurred in the middle and upper parts of Longwangmiao Formation, with most commonly as a crystalline dolomite and less commonly as a gain dolomite; the percentage content of dolostone in dolomite ranged from 48.6% to 75%, ratios of Mg/Ca were generally small, and positive and negative relationships between content of MgO and content of CaO were identified, respectively; the dolostones were generally characterized by high contents of Fe and Na while low contents of Sr and Mn, and only a part of dolostones had high content of Mn; compared with composition of contemporaneous seawater, most of dolostones were characterized by positive δ13C values and negative δ18O values. Based on the analyses of regional geological setting and geochemical characteristics, the dolomite in Longwangmiao Formation was mainly from the seepage-refluxion dolomitization, while evaporative-concentration dolomitization and burial dolomitization were not developed. In general, the dolomitization of Longwangmiao Formation was not complete. Furthermore, through the dolomitization model of Longwangmiao Formation, the distribution of sedimentary facies as well as the controlling effect of dolomitization on reservoir, the favorable reservoir was predicted, and was mainly developed around Qiyueshan fault zone. Keywords: Geochemistry, Dolomitization, Reservoir, Prediction, Longwangmiao Formation, Sichuan Basin