Petroleum Accumulation Model Of Ordovician Reservoir In Tahe Oilfield

Ordovician carbonatite reservoir in the Tahe Oilfield is the largest one found in marine carbonatite reservoir currently.It's constructed by the multi-phase tectogenesis and the ancient karst,and it's a complex reservoir which dominate reservoir by fractures.Hydrocarbon Multi-period petroleum accumulation and late intensive deformation leaded to the reservoir formation and evolution.Fluid distribution and accumulation model is not yet clear,which has caused great difficulties in choosing the benefitial blocks and the further exploration work.This paper makes use of new theories,new techniques for the first time,based on in-depth analysis the conditions of the reservoir,studing the period of hydrocarbon accumulation and accumulation model of the fractured-cavernous reservoirs. This will not only have great significance to the exploration in this area, but also enrich the theory model for formation of carbonate reservoirs in the similar geologic conditions with Tahe Oilfield in the western China.The paper employ many methods to determine the reservoirs forming stages and hydrocarbon charging history in Tahe oilfield,and point out that the formation of present industrial reservoirs is the result of the sustainable process started from early Hercynian to Himalayan period.This paper firstly points out that early Hercynian is the important hydrocarbon charging stage of Aydin area in the northwest of Tahe oilfield,while late Hercynian is the most important hydrocarbon charging stage of main body region in the Tahe oilfield,and the Indosinian-Yanshanian period also is another period for hydrocarbon charging.Condensate gas in the east of the Tahe oilfield forms in the Himalayan period.Thus this paper further clarify the contribution of different hydrocarbon charging stages to the reserve nowadays and their distribution,and further make clear the geo-fluid distribution and their controlling factors.Distribution of oil and gas in this area is characterized by strong non-uniformity in the distribution of carbonate reservoir,the porous space complexity and their connectivity,as well as the multi-phase hydrocarbon charging,which result in oil and water complex distribution in the Tahe Oilfield Ordovician reservoirs,in details,no uniform oil-water interface occur in the the whole oilfiled.In one word,this oilfield is a composition of the oil and gas reservoirs with different sizes and different energy.Main Controlling factors are as follows:â‘ The degree of reservoir development controls over oil and gas distribution in the plane;â‘¡relatively independent of the fractured system,as well as the influence of multi-phase accumulation of oil and gas,causing the huge discrepancy of fluid nature in the vertical and horizontal direction;â‘¢Under the influence of the integrity of the cap, the fluid nature differences exists in all districts and regions;â‘£controlled by the connectivity of karst cave seam during stages of hydrocarbon charging.This paper shows the migration pathways and direction of Ordovician hydrocarbon in the Tahe Oilfield through molecular parameters of hydrocarbon.In particular,the combination of the hydrocarbon tracing research and the latest interpretation of the fractures depict the advantage migration pathway and the main direction of migration of the Ordovician reservoir in this region.A detailed analysis of the fault and the percolation condition of the unconformity are carried out on the conditions of hydrocarbon migration in Ordovician carbonate and evaluated the conditions of the Lower Ordovician favorable permeability reservoir zone.In accordance with the characteristics of Ordovician fractured reservoirs,a " karst-fractures and cavities-double structure accumulation model" has been established for the first time,the Ordovician reservoir model can be referred to as "Ordovician karst-fractures and cavities -double structure accumulation model "and can be divided into karst - early fractured,karst-fractured Superposition and transformation,and karst -late fractured three subordination model.This thesis has pointed out that the middle section of the western slope in the Tahe Oilfield is the most important region where the large-sized hydrocarbon accumulation in the early Hercynian period in the Akekule uplift.It is necessary to deepen understanding and re-evaluation for the Early Hercynian resources.The western slopes,extension of the Western Tahe Oilfield,has much potential for further exloration.The early Hercynian crude oil discovery suggest new clues to further evaluation the early Hercynian resource potential and exploration direction in the middle of the western slope in the Tahe Oilfield.