A critical review of self-diverting acid treatments applied to carbonate oil and gas reservoirs

Abstract

Carbonate reservoirs generally achieved relatively low primary resource recovery rates. It is therefore often necessary to clean those reservoirs up and/or stimulate them post drilling and later in their production life. A common and basic carbonate reservoir cleanup technique to remove contaminating material from the wellbore is acidizing. The efficiency of acid treatments is determined by many factors, including: the type and quantity of the acid used; the number of repeated treatments performed, heterogeneity of the reservoir, water cut of the reservoir fluids, and presence of idle zones and interlayers. Post-treatment production performance of such reservoirs frequently does not meet design expectation. There is therefore much scope to improve acidizing technologies and treatment designs to make them more reliable and effective. This review considers acid treatment technologies applied to carbonate reservoirs at the laboratory scale and in field-scale applications. The range of acid treatment techniques commonly applied are compared. Differences between specific acid treatments, such as foamed acids, acid emulsions, gelled and thickened acid systems, targeted acid treatments, and acid hydraulic fracturing are described in terms of the positive and negative influences they have on carbonate oil production rates and recovery. Opportunities to improve acid treatment techniques are identified, particularly those involving the deployment of nanoparticles (NP). Due consideration is also given to the potential environmental impacts associated with carbonate reservoir acid treatment. Recommendations are made regarding the future research required to overcome the remaining challenges pertaining to acid treatment applications.