Test on the dolomite dissolution under subaerial temperature and pressure

Secondary porosity resulting from the dissolution serves as the main oil reservoir spaces in carbonate rock. The dissolution mechanism of carbonate rock needs to be researched from the point of view of simulation test. In this paper, several groups of dissolution contrast tests have been made for three types of the dolomites with or without adding anhydrite in both acetic acid and CO2 solutions under subaerial temperature and pressure. Several findings from the tests are as follows:(1)Under subaerial temperature and pressure, acetic acid has more solubility than CO2 for carbonate minerals; Besides, the products of the dissolution in acetic acid approach the chemical measurement of the solute, while Ca2+ is released and Mg2+ is detained in CO2 solution; (2)Adding anhydrite in CO2 solution remarkably improves the dissolution effectiveness of the dolomite under subaerial temperature and pressure, which makes the products of the dolomite dissolution approaching the chemical measurement by inhibiting the release of Ca2+ and speeding up the release of Mg2+ ; (3)For pure dolomite with over90% dolomite component, adding anhydrite will lead to the dissolution of the dolomite and increase in total amount of the released Mg2+ and Ca2+. On the contrary, if the anhydrite in the solution deposits, the dolomite will deposit, too. The findings of the test in the paper can help us make out the process of the dolomite dissolution under subaerial temperature and pressure, especially the dissolution of dolomite associated with gypsum as well as the corresponding process of karst and the forming mechanism of secondary porosity.