Spraberry Permeability From Build-Up Curve Analyses

The application of a method for analyzing pressure build-up curves to determine the effective permeability in the Spraberry is presented. Sixteen Upper Spraberry wells of the Driver area are analyzed and show variations in the in-place effective permeability of 2 to 183 md. Since these values are much larger than the.5 md, or less, reported for the matrix rock, a large part of the vertical fractures noted in Spraberry cores must be considered native to the formation. The effectiveness of the well fracture treatment in connecting the well bore to the native fracture system is analyzed by comparison of the effective permeability as determined from the PI test to that obtained from a pressure build-up curve. These results show that the fracture treatment is sufficiently effective in connecting the well bore to the native fracture system to yield a flow capacity within about ?50 per cent of that dictated by the native fracture system. About two-thirds of the wells show some degree of local blockage. Introduction Fractured reservoirs have been known in the past: However, during the past two years the Spraberry formation has directed the attention of the petroleum industry to a study of the performance of a fractured reservoir. The large variation in the number of fractures noted in Spraberry cores, the large variation in the producing ability of offset wells, the dramatic effect of well treatment on well productivity, the unknown quantity of oil stored in the fractures and matrix rock, and the unknown oil to be recovered were part of the initial Spraberry puzzle. In this type reservoir where the well treatment is an important factor in determining the productivity, it is particularly desirable to determine the in-place flow capacity of the drainage area at distances far removed from the well bore. This value, when compared to the flow capacity obtained from a PI measurement, will show the effectiveness of the well treatment (completion, fracture treatment, acidization, etc.) in establishing a flow capacity in the vicinity of the well bore equal to that in the more remote region. The object of this paper is to show the application of a method of pressure build-up analysis for this purpose in studying the Upper Spraberry formation in the Driver area.