Horizontal-Well Pressure Analysis

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Abstract
Summary: This paper presents an analysis of the pressure-transient behavior of a horizontal well or a drainhole. The performances of horizontal wells and fully penetrating vertical fractures are compared. Dimensionless wellbore pressures are computed for two classic boundary conditions: infinite conductivity and uniform flux. Results are presented as pseudoskin factors and as type curves. In addition to conventional pressure-vs.-time type curves, derivative type curves from pressure/time predictions are presented. The derivative approach we discuss is applicable to a broader range of problems than that considered here.Computations suggest that horizontal-well productivity is governed by two parameters: (1) the dimensionless well length, LD[LD=L/(2h)k2/k], and (2) the dimensionless well radius, rwD (the ratio of well radius to well half-length if the formation is assumed to be isotropic). Results indicate that horizontal-well productivity (infinite-conductivity idealization) is almost identical to that of a fully penetrating vertical fracture of infinite conductivity if LD >4.0. This result shows that horizontal wells may perform better than vertically fractured wells if nonideal aspects associated with vertically fractured wells, such as limited conductivity or height, are taken into account.Results have been obtained for the range 0.1≤LD≤100 and for the range 10−4≤rwD ≤10−2; these ranges should encompass expected values of horizontal-well length, reservoir height, and the ratio of vertical and horizontal permeability. Pressure responses and pseudoskin factors are calculated for four different well locations within the productive interval. The pseudoskin factors are insensitive to well location.