TIAN Wen1,2
(1. Postdoctoral Scientific Research Workstation of Shengli Oilfield Company, Dongying 257000, China;
2. Exploration and Development Research Institute, Shengli Oilfield Company, Sinopec, Dongying 257022, China)
Abstract: In this study, we use a 0.2% hydrochloric acid solution to dissolve different types of the Lower Paleozoic carbonate rocks in the Zhuanghai Area of Shengli Oilfield in order to simulate the dissolution process of carbonate rocks under supergene conditions (22 ℃, 1.0 MPa). The scanning electron microscopy observation and ion concentration analysis have been applied to study differences among the dissolution of different types of carbonate rocks by atmospheric fresh water under supergene conditions. The experimental results show that selective dissolution occurred due to both rock structures and mineral compositions. After the dissolution by water, the residual dolomite mostly has honeycomb structure, while the residual calcite has crystal cone drusy structure. The dissolution rate ranking is subsequently decreased in following order: dolomitic limestone > argillaceous dolomite > oolitic limestone > limestone > gray dolomite > dolomite. The contents of Ca2+ and Mg2+ released from limestone vary from 6.35 to 7.08 mmol/L, which is significantly higher than those from dolomite (6.005 to 6.368 mmol/L). The overall dissolution rate of limestone is greater than that of dolomite. The reason why dolomitic limestone has the highest dissolution rate is because the small amount of dolomite in dolomitic limestone has facilitated the dissolution of calcite and improved the dissolution effect of reservoir. Under natural geological condition, data of the conventional log, imaging log, and drilling log show that dissolution pores and holes are developed in limestones because their dissolution scale and strength are larger than those of dolomites. Overall, the karst corrosion characteristics of carbonates in natural geological condition are consistent with the results of water-rock experiments in this study. In conclusion, the limestone is easier to be dissolved than the dolomite under the condition of supergene atmospheric water. Especially, the dolomitic limestone can be most easily dissolved.
Keywords: dissolution; simulation experiment; carbonate; the Lower Paleozoic; the Zhuanghai Area
ACTA MINERALOGICA SINICA Vol. 39, No.1, 2019, page 108-116
