Origin And Distribution Prediction Of Dolomite Reservoirs In The Kelimoli Formation In Western Ordos Basin

The Ordovician Kelimoli Formation in the north of the Tianhuan is an important exploration area and target stratum in the west of the Ordos Basin.In recent years,many exploration wells have found good gas display and low gas production in the Dolomite section of the Kelimoli Formation,but the unclear distribution of effective dolomite reservoirs is an important factor restricting exploration.Therefore,in-depth study of the characteristics,genesis and development of the Dolomite reservoirs has important theoretical significance not only for the reservoir understanding of the area,but also provides important geology for the exploration and deployment of the Ordovician Kelimoli Formation in the north of the Tianhuan.According to the previous studies,based on the theory of sedimentology,reservoir geology and geochemistry,combined with regional geological background,field outcrop,logging interpretation,core and thin section observation,the paper concluded that the tableland marginal grain bank and bioclast bank facies is the favorable facies belt for the development of the Ordovician Kelimoli reservoir in the study area,the reservoir lithology is mainly residual sand dolomite and fine-grained dolomite,the type of reservoir space is dominated by intergranular dissolved pores and dolomite intergranular dissolution;logging interpretation,capillary pressure and industrial CT experiments show that the Kelimoli Formation has good physical properties,and the porosity is generally 2.5%?4.5%;combined with geochemical tests such as carbon and oxygen isotopes,trace elements,strontium isotope,rare earth elements and cathodoluminescence,it is proposed that the Kelimoli Formation dolomite is mainly composed of shallow buried dolomitization;diagenetic-pore evolution analysis shows that meteoric fresh water dissolution and dolomitization are the main causes of pore development in the dolomite reservoir of the Kelimoli Formation in the study area;it is pointed out that the tableland marginal grain banks micro-facies and dolomitization are the main factors controlling the distribution of the dolomite reservoirs in the study area.It is predicted that the favorable dolomite reservoirs of the Kelimoli Formation in the study area are mainly developed in the area east of Yi 27-Le 1-Ren 4-Liuqing 7-Mountain Qinglong,ending at the western boundary of the slope facies.