Prospect of Ultra-Deep Petroleum Onshore China

Abstract

A series of breakthroughs have been achieved in the exploration of ultra-deep formations onshore China as geological understanding and technologies progress, such as Tarim Basin, Sichuan Basin, Bohai Bay Basin. Some new understandings are put forward suggesting that ultra-deep petroleum potential should be beyond expectation: hydrocarbons are controlled by rift valleys in the pre-Cambrian in China, conventional marine carbonate hydrocarbon source kitchens and scattered liquid hydrocarbons in source rocks are cracked to provide a large scale of gas, clastics in ultra-deep formations develop excellent source rocks, the low limit of gas generation is extended and the upper temperature limit for ultra-deep oil cracking without catalysis is beyond 230°C, the low pore radius limit is different for different types of reservoirs and hydrocarbon accumulating mechanisms. The preservation of three types of carbonate karst reservoirs and three types of clastic reservoirs as well as the physical properties of volcanics are slightly affected by burial depth, and it is predicted that favorable reservoirs are widely spread in ultra-deep formations. Carbonate karst, source rock and clastic reservoir interbeds are associated effectively in large ancient uplifts and slopes close to source rocks, faults control hydrocarbons and volcanics form accumulations nearby sources. This decides that ultra-deep carbonates, clastics and volcanics can all form large accumulations, but the abundance of reserve is relatively low. In Chinese ultra-deep formations, there are remaining petroleum resources of 162.9×108t, gas of 16.3×1012m3, nine practical exploratory areas, 14 relay exploratory areas, and a great potential of exploration. In future, ultra-deep carbonates are an important relay area for oil and gas, ultra-deep clastics are secondarily important, and ultra-deep volcanics are and important area for further study.