Gas production from the Devonian Shale is attributed to the ability to connect the natural fracture systems that occur throughout the shale. Hydraulic fracturing has long been standard practice, and is required for most shale wells to produce appreciable gas flows. Since the mid-1980’s most operators have used straight nitrogen as the fracturing medium, believing residual water from foam fracturing treatments delays or reduces gas flow from the shale. Nitrogen fracturing, however, increases the difficulty of stimulating multiple zones perforated over long intervals, another aspect of successful shale well completion. Conventional fracturing treatments currently apply high pump rates (>50 MSCF/MIN) and ball sealers dropped throughout the job in an effort to maximize zonal coverage. However, post-frac production logs indicate that some perforated zones do not contribute to the flow. Coiled tubing operations provide a system with which each zone in a multi-zone completion can be isolated, treated and monitored individually. The ease of downhole relocation with coiled tubing allows several zones to be treated in a continuous operation. A broad range of frac gradients has been exhibited in every wellbore treated to date, indicating that conventional treatments will never achieve total zone coverage. While some gradients are so high they cannot be fractured even when isolated, zone coverage has improved by greater than 20% compared to conventional treatments. Early treatments indicate that coiled tubing fracturing offers a slight economic improvement over conventional treatments. Treatment costs have been comparable, while coiled tubing treatments have achieved marginally higher production rates. Results should improve, however, for at least two significant reasons: additional reserves are made available due to improved zone coverage; and job design is in the early stages of development. The importance of rate and volume are being assessed and early indications are that both will contribute to improved economics.

You can access this article if you purchase or spend a download.