Experimental simulation of dissolution and alteration of buried organic acid fluid on dolomite reservoir

Key words:  dolomite  internal corrosion  simulation experiment  physical properties of rocks  micro-corrosion characteristics

Abstract:

In order to study the processes and effects of dolomite dissolution by organic acid under burial environment, the reactions of acetic acid (initial 0.2%) with sparry oolitic ash dolomite, sparry oolitic dolomite, and silty-fine dolomite were investigated using continuous flow diagenesis simulation system. The results show that the total amount of Ca²⁺、Mg²⁺ released from dolomite is (13.19-20.48)×10-3mol/L. The dissolution quantities of dolomite reduce with the increase of burial depth. The weight lost of the samples on average is about 1％.The average porosity increases by 5％, and the average permeability rises as high as 300％. The results also indicate that the organic acid can still exist in deep burial environment, and it can also strongly dissolve dolomite. The internal pores and throats of dolomite are corroded to enlarge and interconnect, resulting in increased bulk volume of pores and throats but decreased total amount. Burial dissolution effect is significant, especially in permeability property. Inter-crystal and intra-crystal dissolution pores develop in dolomites, and the dolomites are eroded into honeycomb-like pores on the rock surface. The inter-crystal fractures of dolomite are enlarged by dissolution and become interconnected. The micro-corrosion characteristics of dolomite are beneficial to the accumulation and migration of oil and gas.