Reservoir Control Mechanism of Dolomite and Sulfate Rock Compound Palaeokarst in Weathering Crust

Abstract

He, J.; Lian, Z.H.; Yu, H.J.; Huang, X.B.; Zhao, Z.J.; Yao, J.; Tang, X.J., and Li, X., 2020. Reservoir control mechanism of dolomite and sulfate rock compound palaeokarst in weathering crust. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 768–774. Coconut Creek (Florida), ISSN 0749-0208.In the diagenetic environment of meteoric freshwater, the compound palaeokarst of dolomite and sulfate rock is conducive to the formation of a storage and seepage network in the rock, which is key to the development of most evaporative marine facies reservoirs. Taking the Majiagou Formation in the central Ordos Basin as the study object, this research used a detailed description of drilling cores, realistic writing of typical karst outcrops, and sample analysis to determine the coupling relation between two kinds of rock weathering crust paleokarst. The salinity of seawater changed frequently in the sedimentary period of Ma 5; dolomitic flat, gypsodolomite flat, and anhydrite flat occurred alternately in the basin margins; and a set of compound rocks of dolomite and sulfate rocks deposited. After deposition, Ma 5 member uplifted with the Huabei platform, experiencing weathering and erosion, causing various types of dissolution pores and vugs to appear in the residual weathering crust formation. Dolomite with anhydrite concretion deposited in a gypsum-bearing dolomite flat environment laid the foundation for reservoir development, and the preservation degree of this kind of formation and karstification intensity of weathering crust karst complex are key to the formation of high-quality reservoirs. High-quality reservoirs are mainly located in the overlapping area of the gypsodolomite flat and weathering crust palaeokarst platform on the plane, and in the vertical vadose zone and part of the horizontal phreatic zone longitudinally.