Characterization of Carbonate Reservoirs and Main Controlling Factors Research

This study deeply explores the characteristics of the dolomite reservoir and its controlling factors in the Ordovician Majiagou Formation in the southern Gaoqiao area of the Jingbian gas field in the Ordos Basin, aiming to provide a more accurate scientific basis for oil and gas exploration. The study reveals the petrological characteristics and reservoir properties of the reservoir through core analysis, thin- section observation and porosity and permeability testing. The results show that the reservoir in this area is dominated by mud-crystalline dolomite and crystalline dolomite, especially mud-crystalline dolomite shows excellent storage and permeability performance due to the development of pore-soluble pores. The porosity mainly ranges from 2% to 6%, with an average porosity of 3.03%, and the permeability mainly ranges from 0.01 to 5 mD, with an average of 2.14 mD. The analysis of the main controlling factors of the reservoir shows that karst plays a decisive role in the development of dolomite reservoirs, and especially the formation and distribution of the paste-solution pores have a significant influence on the storage and seepage performance. The depositional characteristics of gypsum nodules and their distribution pattern during the rock-forming process have an important influence on the porosity and permeability of the reservoir. Differences in the physical properties of the reservoir in the sedimentary microphase environment have a significant impact on the reservoir performance, in which the microphase reservoir containing gypsum cloud ping exhibits higher porosity and permeability. In addition, reservoir destructive primary control factors, such as compaction and pressure-solubilization effects and cementation and filling effects, negatively affected reservoir properties. Taken together, this study provides important scientific support for understanding the formation mechanism of dolomite reservoirs in the region, assessing the hydrocarbon resource potential, and guiding future exploration activities.