A brownfield in Colombia, produces from the Caballos formation, a highly laminated sandstone formation with permeability of 50 to100 md. The field is under water injection, resulting in calcium carbonate scaling; thus, these wells need to be acidized routinely although the water cut often exceeds 90%. Initially, straddle packers were used to divert the treatments mechanically across the laminated sands, which required a workover rig. To reduce the cost of treating these wells, recent treatments were bullheaded down the tubing casing annulus at the highest possible matrix rates, resulting in mixed results. Water cut increased with no or an insignificant increase in oil production. Hence, a diversion technique/fluid was needed that would provide effective zonal coverage similar to that obtained using straddle packers. The viscous disproportionate permeability modifier (VDPM) fluid was developed for this application. The initial treatments, performed by pumping alternate stages of acid and a VDPM fluid, increased oil production as much as 300% while reducing the water cut by up to 10%. In these cases, the increase in production is equal to or better than wells treated selectively with straddle packers. The use of a VDPM fluid has been shown to be capable of improving zonal coverage, increasing oil production, and decreasing water cut in formations without natural fractures or fissures. During the treatment, the treating pressure increases or remains constant while, in core flow tests, the pressure increases sequentially when injecting acid after each stage of diverter. Despite this, the final effective permeability to oil increases and the effective permeability to water decreases significantly. The VDPM fluid reduces the effective permeability to water up to 80% in a water-saturated core. In the field, the permeability and the length of the interval(s) to be treated determine the number, volume, and viscosity of the VDPM fluid stages based on previous core flow studies. The use of the VDPM fluid has the potential to increase the economic viability of producing this particular field in Colombia and other similar fields. The properties of the VDPM fluid are particularly advantageous when repeatedly treating wells in mature fields on water injection.
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