Shape Factor, CA, Expressed as Skin, sCA

Summary This work presents the conversion of the shape factor, CA, to a pseudosteady-state skin term, sCA. When the shape factor is expressed as a skin term, it becomes easier to see the effect that a well placement in a given drainage area will have on the wells performance. Skin factors for published drainage shapes and well locations are given. Discussion In attempting to calculate interference effects of well locations on production forecasts, it was found very convenient to express the shape factor, CA, as a pseudosteady-state skin term, sCA. When using pseudosteady-state flow pseudosteady-state skin term, sCA. When using pseudosteady-state flow equations, the effect of a well not located in the center of a radial or square drainage area becomes immediately apparent when the shape factor is expressed as a skin term. The general pseudosteady-state equation in terms of CA for oil, gas, or water can be written as ..........................................(1) By using an effective drainage radius, r,', to maintain an equivalent reservoir volume ..........................................(2) and the shape factor for a well at the center of a circular drainage area (CA =31.62), we can obtain the familiar radial flow pseudosteady-state equation ..........................................(3) Introducing a reference shape factor term, we can write ..........................................(4) ..........................................(5) Defining a pseudosteady-state skin factor, sCA, as ..........................................(6) we have, referencing to the center of a circle (the classic analytical solution) with CA, ref = 31.62, ..........................................(7) or, referencing to the center of a square (field and model situations) with CA, ref = 30.8828, ..........................................(8) Values of scA referenced to the center of a circle or square are tabulated in Table 1. Values of CA in Table 1 were obtained from Ref. 1 Constant wellbore pressure production forecasts for wells not in the center of a circle are made conveniently by using the concept of effective wellbore radius with and from Ref. 2 and . Nomenclature A = drainage area, ft2 [M2] B = formation volume factor CA = shape factor D = nondarcy flow constant JPT February 1985 p. 321