Document Type : Research Paper
Abstract
Growing applications of horizontal well technology warrant attempts towards modelling for more realistic phenomena. In the study of performance of horizontal wells in layered reservoirs, particular issues have been dealt with; however, existing models restrict the number of flow regimes. In this research, the pressure distribution of horizontal wells in layered reservoirs was presented in the form of dimensionless pressure and dimensionless pressure derivative functions of reservoir system properties and fluid properties without restriction on the number and type of flow regimes. The model considered the effect of the interface on pressure response and the effect of cross flow. From the results obtained, dimensionless pressure depends on the type of interface, degree of cross flow, dimension of layer, regional well parameters, and regional rock and fluid properties. Dimensionless pressure was found to increase as the degree of cross flow reduces. Dimensionless pressure decreases as layer thickness increases. The type, interval of subsistence, and number of existing flow regimes depend largely on the reservoir system parameter, the location of the interface relative to the well, and the degree of cross flow. A horizontal well in a bound layered reservoir experiences a minimum of eleven (11) flow regimes, including some transition periods at full flow, i.e., when all the external boundaries are felt. During a flow period, the type and number of flow regimes that may occur, as well as the duration of existence, are determined by the values of parameters, the geometry of the reservoir, the fluid properties and the well architecture selected. The model was seen to produce a series of radial and linear flows along the individual principal axes or combinations of any of the three principal axes. Each flow regime could be recognised by its characteristic signature in the log-log graph plots of the pressure and pressure derivative versus time. Flexibility of the model in this article allows for an easy switch of reservoir features between isotropy and anisotropy, single compartment and layered, and homogeneity and heterogeneity.
