Early Forecast and Evaluation Study on Chief Source Rock in Baiyun Depression

Key words: 
• condensed section /
• seismic facies /
• sedimentary facies /
• organic maturity

Abstract: Source rock is very important for deepwater. Because there is no well piercing the Eocene strata, regional correlation method is applied to identify the source rock and define its distribution in Baiyun Depression, including the correlation of subsidence rate, sedimentary facies, seismic facies and seismic velocity lithology with the adjacent areas. The condensed section in the Paleogene strata of Baiyun Depression has three features: ① parasequences moved forward the shore; ② the supply of terrigenous detrital material was not enough; ③ semideep lacustrine fine sediment developed well. The seismic reflection characters are well corresponding to the favored source rock. The seismic facies of mediumweak amplitude, mediumlow frequency and mediumhigh continuity of lake progressive system tracts of Enping and Wenchang Formation in Baiyun Depression is the area of favored source rock. A forecast model is built up for the degree of organic maturity of source beds with single well and the mudstone porosity which can be got easily from the seismic information. This model is then applied to evaluate the thermal evolution degree of the source beds in Baiyun depression preliminarily. Based on the research of Baiyun depression, this paper represents a Methodology of evaluation on source rocks of deep water. This methodology includes five aspects: (1) analysis of sequence stratigraphy to determine the main formation of source rocks, (2) analysis of seismic reflectance signature to determine the occurring position of source rocks, (3) prediction of vitrinite reflectance based on mudstone velocity to determine the maturation of source rocks, (4) prediction of types of organic facies based on the conversion from sedimentary facies to organic facies, (5) comprehensive evaluation to select optimum hydrocarbongenerating sag. 