Use of a CO2-Hybrid Fracturing Design To Enhance Production
- Chris Carpenter (JPT Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- July 2015
- Document Type
- Journal Paper
- 118 - 120
- 2015. Society of Petroleum Engineers
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- 260 since 2007
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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 173380, “Use of a CO2-Hybrid Fracturing Design To Enhance Production From Unpropped-Fracture Networks,” by Lionel H. Ribeiro, Huina Li, and Jason E. Bryant, Statoil, prepared for the 2015 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 3–5 February. The paper has not been peer reviewed.
This paper introduces a new carbon dioxide (CO2) -hybrid fracturing-fluid design that intends to improve production from ultratight reservoirs and reduces freshwater usage. The authors present simulation work that demonstrates how CO2, with its low viscosity, can extend the bottomhole treating pressure deeper into the reservoir and generate a larger producible surface area. They also present experimental evidence that CO2 leaves behind higher unpropped-fracture conductivities than slickwater (hereafter designated as FR water).
The theory of improved recovery with the CO2-hybrid fracturing design is predicated on the assumption that current stimulation treatments with water- based fluids understimulate the reservoir by leaving behind damaged (conductivity-inhibited) stimulated regions deeper in the reservoir. Conversely, CO2 can improve drainage and recovery from these unpropped regions by (1) extending the bottomhole treating pressure deeper into the reservoir, (2) improving the stimulated fracture coverage by increasing both the number of stimulated fractures and their density (number of fractures per unit of volume), and (3) improving the conductivity of the stimulated unpropped channels.
The ambition is that CO2, with its subwater viscosity, can stimulate even more reservoir surface area per unit volume pumped (Fig. 1). To do so, the proposed design is not limited to a simple sequence (CO2 pad followed by gelled slurry) but may also include several variations such as alternated slugs of CO2 and gelled slurry to enhance the fingering of CO2 through high-viscosity slugs, or low-viscosity alternatives to CO2 such as nitrogen or compressed gas.
One of the key hypotheses in the success of the CO2-hybrid design is that a large portion of the stimulated surface area contributes significantly to production. If this is the case, stimulated unpropped fractures bolster the effective drainage area and accelerate production. To test this hypothesis, we conducted cracked-core- conductivity experiments on Middle Bakken samples for three fracturing fluids (CO2, base water, and FR water). The experimental procedures and results are discussed in detail in the complete paper.
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