Comprehensive Approach to Production Stimulation of Massive Cold Heterogeneous Carbonate Formation using Coiled Tubing

Abstract

Abstract The Orenburg oil, gas and condensate field (OOGCF) is one of the largest fields in the Volgo-Urals region of Russia. It is characterized by complex formation lithology, underlying water, low bottomhole temperature and significant reservoir depletion making successful matrix acidizing particularly challenging. Existing wellbore equipment prohibits the use of inflatable packers. Therefore only chemical diverters can be used for treatments. Thorough engineering and previous acidizing experience in this region lead teams to select the following technologies to account for all challenges in stimulation on OOGCF: Viscoelastic self-diverting acid (VSDA). Based on viscoelastic surfactant, VSDA initially has low viscosity. However, while the acid spends, the fluid viscosity increases, redirecting flow to less permeable zones. After the treatment, viscous VSDA losses its viscosity when it comes in contact with hydrocarbons and/or solvent pumped in the preflush stage. Absence of polymers in VSDA eliminates risk of formation damage.Selective diverter for temporarily blocking water-producing zones. This water-based fluid with viscoelastic surfactant initially has high viscosity. During matrix acidizing treatment, the selective diverter is injected into all zones. Its viscosity sharply drops in the hydrocarbon-saturated zones while maintaining stability in water-saturated intervals, thus preventing acid injection in undesirable zones.Foam diverter allows foam to be generated in the matrix and temporarily plug the pore spaces. This causes temporary plugging of the acid-etched channels and allows unstimulated zones to be treated. The main advantage of foam diversion is fast and efficient cleanup, which is especially important for depleted formations.Highly retarded emulsified acid helps create wormholes while treating long intervals with low pumping rate through coiled tubing (CT).CT placement with pumping foam diverter through CT and HCl through CT - Tubing annulus simultaneously to block known thief zones. Up to date 3 stimulation treatments were successfully performed with average incremental gas production of 61% that could not be achieved before on this field. A combination of all solutions and technologies mentioned above allowed to address all challenges related to matrix acidizing on OOGCF field.