This paper presents a simple method to scale production histories from analog wells used to construct type wells to common reference conditions, including average permeability in the SRV, average fracture half length, fracture stage spacing, and lateral length. Analysts need a scaling technique because available analog wells in an area of interest are likely to have varying characteristics that may influence production profiles and averaging procedures based on these profiles. Further, proposed new wells in the area may have design properties (e.g., fracture length, spacing, lateral length) that differ from averages in the analog wells. Scaling solves this problem and reduces the uncertainty in the statistical significance of the analog well data.
The basis for the scaling proposed in this paper is the well-established analytical solution to the linear diffusivity equation for production at constant BHP and the equation for depth of investigation in transient linear flow, both of which are applicable to multiple-fracture horizontal wells (MFHW). The analytical solution is the basis for the "A-root k" analysis often used to estimate average fracture length in MFHW's. The depth of investigation equation is the basis for estimating average permeability in the SRV based on the time at which transient flow ends. Given estimates of permeability and fracture-stage spacing, an analyst can estimate average fracture half-length. Because they can state the analytical solution for transient linear flow in terms of simple dimensionless variables (dimensionless rate vs. dimensionless time), analysts can scale any rate-time profile to selected reference conditions. Scaled rate-time profiles can then be averaged to produce mean, P50, and possibly other type wells at specified probability levels. These reference profiles can then be rescaled to design conditions for undrilled wells This paper provides a workflow and examples based on actual field data illustrating analysis, scaling, rescaling, and type well construction.
The workflow recommended in the paper can be used to construct type wells from groups of analog wells with relatively few "bins" into which wells with similar production profiles are placed. The criterion for placing wells into a given bin will be similarity of production profiles after an analyst scales wells to common reference conditions. Our studies indicate that one or two bins are often sufficient to construct type wells for a given area of a resource play.
Scaling, using workflow proposed in this paper, allows analysts constructing type wells to reduce production histories of wells to common reference conditions before averaging, and then to rescale to design conditions for undrilled wells.