Experimental simulation of dissolution law and porosity evolution of carbonate rock

Experiments of acetic acid (initial 0.2%) with porous dolostone, fractured-porous-vuggy dolostone, porous limestone and fractured limestone were done in a continuous flow diagenesis simulation system to find out the controlling factor of dissolution and dissolution effect. The results show that the dissolution quantity of carbonate rock inversely proportional to temperature and directly proportional to pressure, and the temperature effect is greater than the pressure effect. Therefore, relatively shallow burial and lower temperature environment is more beneficial to the formation of large scale carbonate dissolution pores. Quantitative comparison of porosity volume and permeability variation, and evolution of pores inside the rock before and after the experiment show that pore structure has apparent control over the carbonate dissolution and pore evolution. After dissolution, porous dolomite with homogeneous pore distribution saw rise in pore volume (matrix pore volume) and permeability, and remained as pore type in terms of reservoir space; porous limestone, with significant heterogeneity in original pores and texture, saw significant increase in pore volume and permeability, but the increased pores were fracture type, so its reservoir space turned into fracture-pore type; dissolution increased the permeability of fracture-pore dolomite and fracture limestone remarkably by 2-3 orders of magnitude; and the pores increased were mainly along dissolution fractures, turning the reservoir space into fracture-cave type.