Study Of Marine Carbonate Source Rocks In The Lower Paleozoic

The Tarim Basin is rich in marine oil and gas resources,and a series of large marine oilfields,such as,the Lunan-Tahe oilfields reaching 3 billion tons reserves and the Tazhong carbonate oilfields with reserves of 800 million tons,have been discovered in recent years.The source rock of these marine hydrocarbons is from CambrianOrdovincian,while which is the exact origin is still under debate.Based on geological investication of several outcrops,logging data,analytical results of samples,as well as previous achievements,this paper studies the carbonate source rock of the lower Cambrian Xiaoerbulake Formation in Tarim basin.Some preliminary conclusions have been obtained as follows: First,the Xiaoerbulake Formation source rocks,developed in a restricted platform environment,are mainly mud-sized crystalline dolostone and distributed in the western part of the basin.Second,the Xiaoerbulake Formation source rocks have high TOC,and which are assessed to middle-good source rock,and even to excellence.Organic matter of Xiaoerbulake Formation is mainly derived from Pelagic algae and Acritarchs,and whose type is dominated by type ?-? kerogen without regard to weathering,while the evolution is high mature.Third,trace element characteristics indicate that Xiaoerbulake Formation source rocks developed in good conditions with anaerobic sedimentary environment and high paleoproductivity.Lastly,Xiaoerbulake Formation source rocks have a great thickness and develop stably in Keping and Bachu area,so they have good hydrocarbon-generating potential,while Tabei and Tazhong are poorer.