Geochemical Characteristics and Logging Quantitative Prediction Model Establishment of Source Rocks in Saline Lake Basin—Take the Paleogene of Qaidam Basin as an Example

Abstract

The western Qaidam basin in China is an inland salt lake basin in the Cenozoic arid climate. In recent years, significant breakthroughs have been made in oil and gas exploration in the paleogene lower Ganchaigou formation in this area, and 200 million tons reserves have been discovered. It is proved that the paleogene saline lacustrine source rocks have great potential. Salt lake source rocks in the study area are obviously different from freshwater lake sediments, and their main characteristics are the mixed deposits of hydrocarbon source rocks and salt rocks, gypsum, carbonate rocks and terrigenous clastic rocks, with strong heterogeneity, and the thickness of single layer of source rocks is thin, generally 1.5–3.0 m. The TOC value of source rocks ranges from 0.27% to 1.11%, and the effective source rocks (TOC > 0.4%) account for 56.25%. Chloroform asphalt “A” of source rocks ranges from 0.03% to 0.58%, and the effective source rock (chloroform asphalt “A” > 0.015%) accounts for 100%. In order to quantitatively identify and evaluate the hydrocarbon source rocks in the region. A quantitative model is established between the comprehensive lithological characteristics of logging information and the organic carbon mass fraction, and the hydrocarbon source rock is predicted longitudinally. In contrast optimization on the basis of logging information, the establishment of natural gamma ray - resistivity curve overlapping method (qualitative) quantitative prediction model, according to the comparison of the measured values and the fitted value, when GR logging curve >95 API, RD >40 Ω m. mudstone and grey mudstone as the effective hydrocarbon source rocks in the area, the quantitative prediction model fitting effect is good, the oil and gas resources for the area provides a method for quick support.