Distributive Features and Their Controlling Factors of the Sinian-Silurian Paleoreservoirs of Oil in Sichuan Basin, China

Shugen Liu¹, Wenming Huang², Guozhi Wang¹, Hansong Dai³, Wei Sun¹, Cuihua Chen¹, Wenxin Ma¹, and Bin Deng¹
¹State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, China
²Geological Exploration & Development Research Institute, CNPC Chuanqing Drilling Engineering Company Limited, Chengdu, China
³Northwest Department of CNPC Research Institute of Petroleum Exploration & Development, Lanzhou, Gansu, China

As a superposition basin rich in oil & gas, the Sichuan basin in west China has developed several sets of source rocks, reservoir rocks and cap rocks. The Lower Cambrian and Lower Silurian mudstones are the source rocks and cap rocks for the Lower Paleozoic and older strata. Abundant Sinian-Silurian paleo-reservoirs of hydrocarbon formed in geologic history, and Sinian-Silurian natural gas today was mainly cracked from crude oil because of deep burial and high temperature in the Sichuan basin. The crack of crude oil will result in gas and bitumen in the oil reservoir rocks. The areas in the reservoir rocks with rich bitumen from oil crack are the distribution of the paleo-reservoirs of oil. The Upper Neoproterozoic Sinian reservoir rocks were of two-three phase filling with bitumen, which can widely be found in any Sinian drilling wells and outcrops. However, the Cambrian, Ordovician and Silurian reservoir rocks were of only one-two phase filling with bitumen, which can only be seen locally in the basin. Therefore, the Sinian Paleo-reservoirs of oil widely occurred with local enrichment in the basin as well as its periphery; however, the Lower Paleozoic paleo-reservoirs of oil were scattered with relatively small lithologicstructrual traps.

The distributive features of the bitumen in the Sinian-Silurian reservoir rocks were closely related to their lithology and diagenesis history, which controlled the development of high-quality reservoir rocks. Being both sedimentary and denudation uplifts in the basin, Leshan-Longnvsi Caledonian (Early Paleozoic) paleo-uplift and Luzhou-Kaijiang Indosinian (Triassic) paleo-uplift greatly controlled the distribution of Sinian- Silurian source rocks, hydrocarbon generation history and the distribution of the superior reservoir rocks. Being oil & gas migration and filling areas from the Lower Paleozoic source rocks (Lower Cambrian and Lower Silurian mudstones), the paleo-uplifts in the basin were the most significant factor controlling the development of the Sinian-Silurian paleo-reservoirs of hydrocarbon.

AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013