Multiple Proppant Fracturing of Horizontal Wellbores in a Chalk Formation: Evolving the Process in the Valhall Field

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Abstract Oil production from this chalk field has been improved significantly over the last three years through the use of multiple proppant fractures placed from horizontal completions. Following early successes the engineering effort now focuses on increasing value through engineering innovation and increased productivity. This paper describes, through case histories and field data, the advances made in the design and execution of these completions over the first 13 such wells in the field. Wellbore completion activities and stimulation are now performed as a standalone process through the use of specialized large diameter coil tubing equipment so allowing on-going drilling operations to be performed concurrently. This has significantly reduced daily spread costs while bringing wells on production within a much reduced time frame. This lower cost environment has also allowed innovative field procedures to be developed resulting in further improvements such as proppant plugs for isolation between stimulation zones and treatments using recycled proppant to minimize waste. Treatment design has been refined through downhole pressure monitoring which has allowed empirical frictional relationships to be developed for proppant slurry and coil tubing circulating fluids. This data validates the wellbore tubulars design and allows any weak points in the arrangement to be highlighted for change. An extensive fracturing database is maintained allowing each treatment design to be compared with previous experience in the field. Productivity is the driver for economic success and treatment design requirements have evolved through laboratory testing to account for longer term downhole operating conditions below the bubble point while also improving initial conductivity. Field data to date through PLT logging has confirmed the hydrocarbon contribution from each fracture and this is used to validate, or otherwise, the effectiveness of each treatment. Normalized well productivities continue to improve and the challenge is to maintain the rate of evolution through the improved application of both new and existing technologies. P. 335