Characteristics of high-quality hydrocarbon source rocks and their contributions to reservoirs in the Erlian Basin

The Erlian Basin consists of many sags characterized by multiple provenances, changeable phases and a low degree of thermal evolution.The identification of high-quality source rocks determines the direction of exploration efforts.By building correlations between TOC and HI, and analyzing the changes of organic carbon contents under various sedimentary circumstances, we have shown that stable sedimentary areas such as shallow lakes and relatively deep lakes commonly develop high-quality source rocks, and unstable sedimentary areas like rivers and shallow shore lakes commonly develop poor- or medium-quality source rocks.We can use TOC to classify source rock levels.The source rocks from stable sedimentary areas are divided into high (TOC > 2%), medium (1% < TOC < 2%) and poor (TOC < 1%) quality source rocks.The source rocks from the unstable sedimentary areas are divided into medium (1% < TOC < 2%) and poor (TOC < 1%) quality source rocks.Furthermore, based on TOC values calculated from well logging data, the thickness and distribution of different levels of source rocks can be ascertained.High-quality source rocks have a close relationship with oil and gas reservoirs, and are the main sources of oil to these reservoirs.The source contribution from high quality source rocks is > 70% even though they constitute only 20% of total source rock volume.Consequently, the distribution zones of high-quality source rocks are commonly favorable areas for large scale reserves.