Field Cases to Demonstrate Application of through Tubing Inflatable Anchoring Packer to Selectively Stimulate Vertical Dump Water Injector Wells with Cross Flowing Zones

Abstract

There are few methods to acid stimulate cross-flowing zones in dump water injector wells. Traditionally these wells are stimulated by bull-heading acid from surface or pumping it through Coiled Tubing (CT). The dilution and contamination of the acid while being injected into the formation resulted in no increase in dumping injection rates. Poor post stimulation results are confirmed by spinner survey logs done before and after the conventional acid treatments. Through Tubing Inflatable Anchoring Packer (TTIAP), a new zonal isolation tool conveyed by coiled tubing was successfully used to selectively acidize the targeted zone by isolating the non-desired zones. TTIAP has an effective and reliable high pressure sealing properties at large inflation ratio. Its chemical resistance makes it ideal for selective placement of treating fluids, such as acid stimulation and water shut off fluids.1,2 A non-polymeric Viscoelastic Surfactant based Self Diverting Acid (VES-SDA) system was successfully used to divert and effectively stimulate these vertical dump water injector wells by achieving uniform acid coverage across the whole perforated interval. The VES-SDA is a single stage fluid that has the capability to stimulate and divert in one step. This paper discusses the successful application of TTIAP as a mean of mechanical diversion in the well-bore area to isolate between the "S" aquifer and the "R" reservoir, while VES-SDA acid was used as a mean of chemical diversion inside carbonate formations. The injection evaluation logs showed significant injection rate increase after the new stimulation method. This study marks the first time such a combination was used to stimulate dump water injector wells with crossflowing zones in Saudi Arabia. Field History The limestone reservoir "R" was discovered in 1963. The crude oil production was commenced in November 1966. This reservoir produces 32 degree API gravity oil. The subsea depths of oil producing zones are ranging from 6,900 ft to 7,300 ft. The full-scale oil production from this reservoir was commenced in the middle of 1969 with a reservoir BHP of 3,610 psi. Along with the oil production, the reservoir pressure declined rapidly. By 1975 the reservoir pressure declined to about 2,660 psig. To keep producing the reservoir naturally, it was decided to use the "S" aquifer to maintain the reservoir pressure and laterally sweep the oil in place. Eleven new vertical dump water injector wells were drilled and perforated through the shallow aquifer and the depleted limestone reservoir. As a result a continuous water injection from the aquifer into the reservoir is achieved naturally. As of the end of year 2003, a total of 36 wells were completed in this reservoir, 25 wells are producers and 11 wells are injectors. The average reservoir pressure at the end of June 2003 was 2,805 psig at its datum depth of 7,260 ft subsea. Introduction Traditionally, stimulating wells with production tubing without inflatable assisting equipment meant that formations could not be stimulated selectively or could only be stimulated using less-effective diverting techniques. The ability to isolate individual intervals is imperative to the successful stimulation of a particular zone. The inflatable zonal isolation technique had to be reliable and fast in order to reduce overall treatment costs enabling quick payback.3 Previous failed inflatable attempts from incompatibility with the stimulation chemicals resulted in reducing the inherent advantages of through tubing inflatable technology.