Distribution of favorable lacustrine carbonate reservoirs: A case from the Upper Es4 of Zhanhua Sag, Bohai Bay Basin

Based on core thin sections, logging and seismic data, the distribution of favorable lacustrine carbonate reservoirs is predicted in the upper Es4 of the Zhanhua Sag, Bohai Bay Basin. In the upper Es4 of the Zhanhua Sag, four categories of carbonates are developed, i.e. bioclastic limestones (dolomites), intraclastic limestones (dolomites), arenaceous limestones (dolomites) and argillaceous limestones (dolomites). With core calibrated logs, the electrical characteristics interpretation criteria for various carbonates are established, and the lithofacies sequences of the exploratory well are reconstructed. According to overlying pattern of high-frequency cycles, the short-term cycles of bioherm, carbonate bank and semi-deep lake are divided, and high resolution isochronous formation framework is built. On the basis of the facies characteristics of well tie sections and palaeo-landform background, the carbonate depositional model is established, namely, the reef and bank carbonates are deposited from the largest expansion period to the stable period of lake basin, bank carbonates are mainly distributed on the upper side of synsedimentary faults on the gentle slope or deposited in fault-step lowland on the steep slope while the reef carbonates mainly on fault-step highland on the steep slope. Favorable reservoir types include reef bioclastic limestone (dolomite), bank bioclastic limestone (dolomite), intraclastic limestone (dolomite) and arenaceous limestone. It is possible to predict the distribution of favorable reservoirs according to the depositional model, palaeo-landform analysis and seismic amplitude attributes.