A New Composite Reservoir Model for Thermal Well Test Analysis

Abstract

Abstract-A composite reservoir may occur during any enhanced oil recovery project like steam injection into an oil reservoir. Falloff test analysis in steam injection projects offers a quick way to obtain estimates of the swept volume and steam zone properties. Most of the models used for the analysis assume two-region composite reservoirs with different but uniform properties separated by a sharp vertical interface, which is not very realistic. Strange trends seen on the pressure plots and the errors associated with the volume estimates could be related to the simplifying assumptions of the conventional models. The main objective of this paper is to develop a new analytical model for pressure transient analysis to improve previous results with inclusion of more realistic assumptions. The proposed model is a three-region composite model with an intermediate region in which mobility and storativity decrease as power law functions of the radial distance from the front. The fronts are considered to be tilted due to gravity effects. Steam condensation in the form of heat loss from the steam zone is also included in the analytical model. The new sets of type curves for well test interpretation are generated and verified. Effects of several parameters on the shape of type curves are discussed. The developed model can improve estimations of reservoir parameters using type curve matching and explain the anomalies seen on the data, which cannot be described using the conventional models. The general nature of the model makes it applicable to other types of composite reservoirs created either naturally or artificially.

A Multi-Layer Multi-Region Well Test Model

“…The model presented in the previous section will reproduce many of the composite models with constant properties in different regions listed in the references of [2] and [3]. Notice that if = = 1 and index i is dropped; the equations represent the single layer reservoir model.…”

“…The two-region simplification of composite reservoirs was improved by various analytical composite reservoir models (listed in the references of [2] and [3]). In previous works ( [2] and [3]), two analytical models were developed for the pressure behaviour of a three-region composite model with power-law variation of properties in the intermediate region.…”

“…In previous works ( [2] and [3]), two analytical models were developed for the pressure behaviour of a three-region composite model with power-law variation of properties in the intermediate region.…”

“…This model is improved in this paper to include the effect of gravity in the form of tilted fronts using the concept of multi-layer reservoirs. The model is further improved by adding more intermediate regions to match the smooth (power-law) property variation of models of [2] and [3].…”

“…1). The following assumptions are applied in the development of the model: This model does not include any heat loss effect as it was comprehensively discussed in the previous works ( [2] and [3]). Properties are constant in each region and decrease smoothly from the first region in any layer.…”