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 Optimal Fracture Stimulation of a Moderate-Permeability Reservoir — Kuparuk River Unit, Alaska
C.M. Pearson, SPE; A.J. Bond, SPE; M.E. Eck, SPE; and
K.W. Lynch, SPE, Arco Alaska, Inc.
This paper details the advances in fracture design in the Kuparuk Field. Over 550 wells were fracture stimulated in the 20 to 80 md sandstone, and the significant advances in fracturing design and implementation are documented.
Although a broad range of operational and technical improvements are discussed, the authors state that the overriding design criteria is fracture conductivity rather than job size or fracture length.
The authors state: “The permeability of the proppant pack is one of the most important factors governing the final conductivity of the proppant pack...evaluation of a proppant needs to be made in terms of cost per millidarcy, not cost per pound.”
The paper describes the evolution from small treatments pumped with 20/40 sand proppant to a variety of treatment sizes with larger ceramic proppants. The primary steps taken to improve treatment results were summarized as:
- Removing 100 mesh sand
- Limiting silica flour to pad stage (later eliminated completely)
- Switching from sand to CARBOLITE® ceramic proppant
- Using higher conductivity 16/20 and 12/18 CARBOLITE® proppant
- Increasing treatment size from 20,000 lbm to 60,000 - 150,000 lbm
- Changing fluids to more viscous water based gels
- Increasing gel breaker concentration
These design changes were shown to more than double the post-frac productivity of the wells. Incremental production increases were projected with recent attempts to incorporate tip screenout designs and larger 12/18 CARBOLITE® proppant in all treatments. Applying the new fracturing design by re-fracturing 88 producing wells resulted in an incremental 40,000 bopd, a significant portion of the field’s 300,000 bopd.
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