Characteristics And Distribution Of Dolomite Reservoirs In The Lower Cambrian Xiaoerbulake Formation In Bachu Uplift

Dolomite is an important hydrocarbon and ore reservoir due to its characteristics of relative homogeneity,good reservoir property,high oil and gas production and long stable production time.In recent years,the hydrocarbon exploration in dolomite reservoir has obtained great success,such as the Sulige gas field in the Ordos Basin,the Moxi-Gaoshiti,Yuanba,Puguang gas field in the Sichuan Basin,and the Yaha,Tazhongl in the Tarim Basin.Those explaration practices indicate that the dolomite reservoir has great potential for oil and gas exploration.In view of the current urgent problems on Cambrian dolomite reservoirs in Bachu uplift,multiple theories and methods from subjects including carbonate sedimentology and petrology,carbonate reservoir geochemistry,carbonate log-geology,carbonate reservoir geology,have been integrated into this dissertation,leading to a systematic research on sedimentary environments,reservoir petrology characteristics,physical parameters,and major storage space,the genesis type of dolomite,forming mechanism and controlling factors.At last,the horizontal favorable distribution area and vertical distribution strata were researched according to reservoir contrast and regional paleo-geography framework.The results of the paper show that the Bachu uplift lied in the restricted platform depositional environment in the Early Cambrian,and the upper and lower Member of the Xiaoerblak Formation are mainly tidal flat and the shoal subfacies,which is favorable facies for the development of dolomite reservoir.In the high energy facies of the platform,the tiny crystalline dolomite,algal arenaceous dolomite,algal dolomite and stromatolite dolomite are generally of high quality reservoirs,which are the type I and II reservoir.The stratified dolomite and micrite reservoirs with low energy sedimentary belt environments are commonly poor physical properties,which are the type III and IV reservoirs.The genesis of mud-silt crystalline dolomite is controlled by Sabkha pattern,and the tiny crystalline dolomite and algal arenaceous dolomite are commonly controlled by the seepage reflux pattern.Generally,the sedimentary facies belt is the most important factor to control the development of the dolomite reservoirs in the Bachu uplift,and the high energy shoal facies is the material base of high quality reservoir.There are also very important factors for the reservoir formation,such as pene-contemporaneous meteoric water dissolution in the early diagenetic stages,the burial dissolution and tectonic rupture in the late diagenetic stages.The sealing of the salt rock cover of middle Cambrian is positive to the preservation of pores.The advantaged dolomite reservoir of the upper Member of Xiaoerblak Formation widely distributes in Bachu uplifts,which is major oil and gas exploration target.Dolomite reservoir distribution of lower Member is affected by the distribution of interior point shoal,for example Fang 1 well and He 4 well,and mainly distributes in northwestern area of Bachu uplift.