Well Test Analysis of a Multilayered Reservoir With Formation Crossflow

Abstract

ABSTRACT The purpose of well test analysis is to identify the type of a reservoir and to determine the parameters of the reservoir quantitatively. This work is about the well test analysis of a multilayered reservoir with formation crossflow. The results are described in two parts. In the first part, the effects of the reservoir parameters such as permeability, vertical permeability, skin, storage coefficient, and the outer boundary conditions on the wellbore response (pressure and layer production rate) were investigated. Some important discoveries are: The wellbore response is observed in three different stages. It is identical to that of the commingled system at early time and and to that of the homogeneous system at late time. Transition occurs at intermediate time.The vertical permeability is the only parameter governing the initiation and termination of the transition from the early time commingled system response to the late time homogeneous system response.The direction of the formation crossflow is determined first by the layer permeabilities and later by the skin factors.The influence of the wellbore storage effect can be minimized by using sandface flow rate from each layer.The outer boundary conditions have only small effect on the wellbore response as long as the transition terminates before the system feels the boundary. In addition, the early time and the late time limiting forms of the wellbore response were derived and some approximation for the late time layer production rate was suggested. In the second part, the non-linear parameter estimation method was applied as a means to determine the layer parameters. Here, two new methods for the initial estimation of the parameter values were suggested and tested, where the early time and the late time limiting values of the layer production rate were used with the conventional pressure analysis for the average permeability and skin of the total system.