Aquifer Water to Replace Fresh Water: The Future of Hydraulic Fracturing in Sultanate of Oman

Abstract Hydraulic fracturing treatments are necessary to increase oil and gas production from challenging tight-gas reservoirs in Oman. These treatments necessitate the use of millions of tons of water to prepare fracturing fluids that are stable in a rheological manner to achieve stimulation success. In Oman, fresh water provided by the desalination plants is typically used for hydraulic fracturing operations. In 2018, operators and service companies began to explore the possibility of treating and reusing produced water for hydraulic fracturing to reserve fresh water for human consumption and agricultural use. (1) The development of a fracturing fluid system that uses saline aquifer, produced, and flowback water and (2) the maintenance of fracturing fluid characteristics to achieve an effective stimulation treatment similar to a freshwater-based fluid are discussed. Hydrocarbon production is accompanied by water having much higher salinity, or total dissolved solids, than sea water. The challenge is converting this produced water into a fluid system that can accept additives and become a rheological-stable fracturing fluid capable of carrying proppant to achieve successful stimulation treatments. The process entails treating produced water using a waste-water treatment process that incorporates oxidation by ozone (ozonolysis), electrochemical treatment, and cartridge filtration. The goal of the treatment is to remove only minerals that hinder the development of crosslinked fluid or cause scale buildup in wells. During this evaluation, it was observed that the content of cations, such as barium, calcium, and iron, in the reservoir water demand low contents of anions (i.e., sulfates and bicarbonates) in the treated water because of severe scale precipitation damage. Extensive laboratory testing was performed, and water-quality criteria were established considering hydration of polymer, breaking efficiencies, risk of scaling, microbial induced corrosion, and premature/overcrosslinking. The result was the development of a novel fracturing fluid with essential characteristics, such as easy preparation, low fluid loss, good proppant transport, low pipe friction, efficient recovery, applicability at bottomhole temperatures as high as 280°F, and minimal risk of wellbore scaling and corrosion. A field test using the new fracturing fluid was conducted successfully. A case history of the fracturing treatment using the new fluid is presented. The results of the laboratory and field trials show that hydraulic fracturing using treated produced water is a viable technology. The impact of engaging in this endeavor of advanced technology development is twofold. First, Oman's scarce fresh water can be prevented from significant depletion and reserved for drinking and agricultural use. It has been estimated that 320,850 m3 of fresh water are used annually in fracturing treatments in Oman. Second, significant cost savings can be achieved from eliminating the disposal of produced contaminated water from oil and gas wells in the Sultanate.