Source rock maturity quantitative prediction using seismic information, a case study in the Ledong-Lingshui Depression, Qiongdongnan Basin

Actual conditions in deepwater areas of Qiongdongnan Basin, such as sparse well controls, shallow-drilling depth, and low-precise formation velocity, are not conducive to organic maturity prediction. Therefore, based on "Ro-Φ" prediction model building for source rock and formation velocity extract, this paper proposes an applicable organic matter quantitative prediction method by the use of seismic data from the Ledong-Lingshui Depression, Qiongdongnan Basin. First we establish "Ro-Φ" prediction model for source rock using the power relationship of organic matter maturity (Ro) and mudstone porosity (Φ) in the study area and its adjacent area. Then using colored inversion method we determine low frequency velocity and relative velocity, and compose relative velocity component and low frequency velocity component to seismic absolute velocity in a moderate broadband. On the comparison of organic matter maturity prediction, "Ro-TTI" method predicts organic matter maturity with higher accuracy, and is suitable for high degree exploration areas. Based on seismic, drilling and geological data, "Ro-Φ" method can be used to understand the spatial distribution of source rocks and hydrocarbon potential, and is suitable for low degree exploration areas. Quantitative prediction results of Paleogene source rock maturity show that Paleogene source rock maturity is relatively high in the center part of the Ledong-Lingshui Depression, and gradually reduced towards the boundary. Source rocks of Upper Oligocene strata including Lingshui formation and Yacheng formation have reached high maturation stage, some of them even have reached over-mature stage which make important contributions to hydrocarbon accumulation in the area. Source rock of Yacheng formation is the most favorable for hydrocarbon generation. Source rock of Lower Oligocene strata is almost in over-matured stage.