Improve acid stimulation efficiency in carbonate reservoirs with high permeability contrast and fluid loss challenges.
An operator in southern Mexico completed a well in the Cretaceous Formation with a 7-in uncemented perforated liner to 16,647 ft [5,074 m] across a gross interval of 292 ft [89 m] with a net pay of 157 ft [48 m]. This zone was a naturally fractured limestone with a formation temperature of 305 degF [152 degC], which presented a challenge to control the high-temperature reaction kinetics and adequately divert acid along the nonfractured sections. The produced oil from this field also has the potential to be incompatible with both HCl and organic acids.
At the same time, an offset well was drilled and completed in the same formation. Because neither well flowed naturally, the operator used coiled tubing to lift the wells with nitrogen. The wells produced an estimated 300 bbl/d and 100 bbl/d, respectively.
Schlumberger recommended NARS treating fluid for higher wormholing efficiency in this high-temperature well. Schlumberger stimulated four perforated intervals with 50 galUS/ft of NARS fluid and 10 galUS/ft of MaxCO3 Acid degradable diversion acid system, while the offset well was stimulated by a competitor with 190 galUS/ft of an organic and inorganic acid blend and 10 galUS/ft of a polymeric diverting acid.
The well treated with NARS fluid cleaned up in just 2 days compared with 10 days for the offset well. Oil production from the well treated with NARS fluid increased from an unstable production of approximately 300 bbl/d to a stable production of 994 bbl/d. In addition, the bottomhole flowing pressure increased from 1,840 psi to 2,700 psi [12.7 MPa to 18.6 MPa]. The offset well continued to produce less than 150 bbl/d after acid stimulation. The production increase in this well and similar results in other wells have made NARS fluid the preferred fluid for stimulating high-temperature fractured carbonate reservoirs.
Challenge: Achieve stable production in a high-temperature limestone formation while minimizing treatment time and costs.
Solution: Apply chelant-base NARS treating fluid to reduce treating volume while increasing well productivity.