Experimental study of acidic and alkaline solvents in oil-wet reservoirs

Chemical reactions occurring between fluid-fluid, rock-fluid, and within the rock itself can lead to the formation of sediment particles into the path of the producing fluid in reservoirs. Moreover, water as the in-situ fluid in reservoir or the fluid mixed with wellhead acids and chemicals for injection inside the reservoir layers can form the damage of water block in a porous media. In this research, the rocks drilled with oil-based fluid from depths 3,567 to 3,394 meters of an oil formation were studied to the effects of wettability, interfacial tension, temperature, and permeability, making the damage-forming situation under reservoir conditions. For this work the related tests were conducted to investigate the effect of acidic and alkaline solvents in removing this type of formation damage. The length and diameter of these loose and dense core samples, cut in various thin sections, were from 8.5 to 9.5 inch and 1.5 to 3 inch, respectively. The measured porosity and absolute permeability were from 0.8 to 400 mD and 5 to 25%, respectively. All oil-wet core samples were prepared to be tested to simulate field injection scenarios over a wide range of injection temperatures and rates, and experimentally quantify water block damage removal in important reservoir lithologies.

The results demonstrated that alkaline solvents as compared to acidic solvents can better remove the damages in the rocks with low absolute permeability. Moreover, these alkaline solvents while having a low injection rate prevented the destructive interactions of these low-permeability rocks, decreased interfacial tension, and increased water-wet reservoir characteristics. Because of this, alkaline solvents at higher temperatures had a better performance relative to acidic solvents, which were accompanied by the rock destruction and the blocking of porous media.