The common well/completion configuration for most shale wells is a horizontal well with multiple transverse hydraulic fractures. This is also becoming a common choice for some tight gas reservoirs. Pressure transient testing of this well/completion configuration has not been considered practical or useful since the extraction of completion parameters (fracture conductivity and half-length) out of a recorded response requires an estimate of effective formation permeability. Obtaining an estimate of permeability directly from a buildup or drawdown test can only be done if data from the radial flow period which reflects this parameter is recorded. Unfortunately, for this well/completion configuration in a low permeability reservoir, this flow period occurs only after extremely long shut-in or flowing times.
In the first part of this paper, the possibility of exploiting some combination of the early time flow regimes present in pressure buildup data to overcome these difficulties is investigated. The paper outlines a specialized data collection and analysis approach that can allow data from relatively short (1 to 2 week) pressure buildups to be used to estimate completion parameters and effective flowing phase permeability. The approach relies on an analysis method which combines parameter estimates obtained from well-known early time flow regime equations with special typecurves that correlate derivative responses prior to fracture interference. The method is most reliable when the fracture radial flow period data is captured since this data is needed to place the measured response on the typecurves more uniquely. Possible methods which allow the collection or re-capture of this desirable early time data, despite large wellbore storage effects, are discussed.
The second part of this paper covers an application of the presented analysis method to pressure buildup data from a BP-operated well completed in the Woodford shale of the Arkoma Basin. This pressure buildup test was done as a field trial to prove the viability of the analysis approach presented here. This section includes a description of the test design/ execution and detailed analysis of the pressure buildup data. A reasonable interpretation of this Woodford shale data is consistent with relatively few, but long planar fractures draining nano-Darcy matrix. This interpretation of the stimulated rock volume is unexpected with implications on stimulation and well spacing strategies.