Microfacies and Reservoir Characteristics of Evaporite-Carbonate Symbolic System: A Case Study of the Jurassic Arab Formation in B Oilfield,Abu Dhabi
In order to explore the strong heterogeneity of evaporite-carbonate symbolic system,based on core and logging data,this paper clarifies microfacies types of Arab Formation in B Oilfield of Abu Dhabi,and analyzes the reservoir characteristics of various microfacies and the main controlling factors of high-quality reservoirs.Twelve microfacies types (MF1-MF12) can be identified in the Arab Formation.Microfacies types and associations indicate that it is a sedimentary system of Sabha tidal flat-lagoon-barrier beach under the background of limited-evaporation.Microfacies control reservoir quality.MF2 and MF9-MF12 have thicker pore throats,better connectivity,and higher porosity and permeability,making them favorable microfacies types for reservoir development.MF2 and MF10 develop dolomite reservoirs,with the reservoir space mainly composed of intergranular pores,residual intergranular pores and intragranular dissolution pores.Grainstone reservoirs are developed in MF9,MF11 and MF12,with the reservoir space dominated by intergranular (dissolution) pores,mold pores and intragranular dissolution pores.The seismic change of relative sea level causes orderly stacking of sedimentary facies belts in longitudinal direction.The difference of microfacies types and diagenesis between different sedimentary facies belts and within the same sedimentary facies belt is the fundamental reason for the strong heterogeneity of the Arab Formation reservoir.The barrier beach and supratidal are favorable facies belts for the development of high-quality reservoirs.The primary intergranular pores of high-quality reservoirs in the barrier beach facies are well maintained and superimposed with significant early exposure and dissolution,resulting in the generation of secondary pores and the further improvement of pore structure.The development of high-quality reservoirs in the supratidal is controlled by early dolomitization and penecontemporaneous dissolution.Dolomitization improves pore structure,which is conducive to early pore preservation.The early dissolution of dispersed anhydrite produces a large number of secondary pores,significantly improving reservoir physical properties.
evaporite-carbonate symbolic systemArab Formationmicrofaciesreservoir characteristicsmain controlling factors of reservoir
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