The acid etched law of carbonate rocks and modification characteristics of microscopic pore structures

Acidizing and acid fracturing are main technical measures for increasing production of Oilfield F in Iraq. To improve the effectiveness of these measures, clarify the rules of acid etched and modification characteristics of microscopic pore structures, this study uses experimental methods such as X-ray diffraction, scanning electron microscopy (SEM), thin section analysis and CT imaging to study the acid etched rules and microscopic pore structures modification characteristics of carbonate rocks in Oilfield F.The experimental results show that: ① Acid etching exhibits selectivity only for minerals and crystals, not for matrix or pores. Hydrochloric acid preferentially dissolves calcite, and calcite with large crystals is more prone to dissolution than calcite with small crystals. Dolomite with small crystals is more prone to dissolution than dolomite with large crystals. ② Acid erosion significantly increases storage space, and pure limestone or dolomite forms large karst caves. Limestone-dolomite mixtures develop connected dissolved pores and sandy dolomite generates intergranular dissolved pores around quartz particles. ③ Reservoirs with well-developed primary pores form large vugs and multiple surface-perpendicular fractures on the rock surface in contact with hydrochloric acid, significantly increasing the storage space and seepage channels. Reservoirs with undeveloped primary pores only form large karst caves or a small number of wormholes on the surface of rocks, resulting in poor deep connectivity. The experimental results provide theoretical guidance for the optimization design of acidizing and acid-fracturing in Oilfield F in Iraq.