Impact of Geological Variation and Completion Type in the U.S. Bakken Oil Shale Play Using Decline Curve Analysis and Transient Flow Character

Hough, Elliott V.¹; McClurg, Thomas ¹
(1) ConocoPhillips, Houston, TX.

A performance analysis study of production data from over 2,300 Bakken oil shale wells in North Dakota, U.S.A., was conducted and the results are correlated with significant geologic and completion type variations across the play. Historical rate-time data were analyzed to identify the transient flow character (wellbore storage, 1/2 slope, ¼ slope or pseudo radial flow) and matched using the Arps equation to estimate ultimate recoveries. Numerical modeling studies were also performed on individual and time-normalized average historical well production to validate reservoir model(s) that best fit the observed well transient production declines.

Differences in transient flow character were defined and mapped using Arps hyperbolic “b” values. Wells completed in areas with a high permeability non-shale Middle Bakken carrier bed, with vertical pressure support from the overlying Upper Bakken and the underlying Lower Bakken Shales, are readily identified and have a characteristic transient decline distinguished by a certain range of “b” values. In other areas, where the Middle Bakken is either much lower perm or not present, producing wells will exhibit a much different transient, shale-dominated, decline and are characterized by an entirely different “b” value.

Integrated analysis that ties well performance to the reservoir geology and completion type lead to much improved reservoir models that can be leveraged to focus development in play sweet spots and optimize completion and well spacing strategies.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.