Building Type Wells for Appraisal of Unconventional Resource Plays

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 185053, “Building Type Wells for Unconventional Resource Plays,” by P. Miller, N. Frechette, and K.D. Kellett, Repsol, prepared for the 2017 SPE Canada Unconventional Resources Conference, Calgary, 15–16 February. The paper has not been peer reviewed. Although the application of statistical techniques to type wells is gaining acceptance, it is often unclear to evaluators how these techniques can be applied to capture accurately the full range of uncertainty in the average single-well estimated ultimate recovery (EUR) for a geologic subset. The objective of the complete paper is to present an integrated work flow that can be used to build P90, mean, and P10 type wells, which represent the range of potential outcomes for the geologic subset in an unconventional resource play. Introduction A common challenge that accompanies new technologies dedicated to the discovery of unconventional resources is how to forecast production and quantify EUR. Early in the life of a resource play, it can be difficult to build type wells because of limited production history and a small well count. Traditional methods would use an analogous-field well model or decline methods to predict future production. Because of unconventionals being a relatively recent development, no late-life fields exist that can be used as direct analogs to understand mid- to late-time horizontal-well behavior in tight unconventional formations. For plays in the early stages of development, because of the relatively small well count and difficulty with a direct analog, the early-time well behavior is also not easily predicted with confidence. There is thus a high degree of uncertainty in both the shape and the magnitude of the type-well profile. Consequently, it is becoming more common for management to ask for an expected type well with a range to capture uncertainty, rather than a single deterministic estimate. The work flow in this paper applies such methods. Methodology Acknowledging Uncertainty. For unconventional resource plays, the two basic sources of uncertainty are the drilling-and-completion (D&C) design and the geological properties that characterize the reservoir. Ideally, one would select a statistically significant number of wells with identical (or nearly identical) geological properties, completions, lateral length, and drilling azimuth to construct type wells. However, this scenario is often far from reality. One solution is to wait until enough wells exist with nearly identical D&C designs and geological properties before proceeding with type-well construction. Obviously, this solution is not practical if management needs to rank assets in the portfolio and justify capital allocation for development of some assets but not others. Therefore, alternative solutions to deal with varying D&C designs and geological properties are to normalize production data for D&C design and to define geologic subsets for areas with similar geological properties.

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