The Influence of Heat Transfer on the Two-Phase Flow Behavior in a Wellbore During Transient Pressure Tests

Abstract

Abstract In this paper a numerical model was developed for the analysis of two-phase flow and heat transfer in a wellbore during a buildup test. The predictions of the model were tested with field data measured in a deep oil well. A detailed study of the influence of heat transfer between the wellbore and the surrounding earth on the bottomhole pressure response during well testing was carried out. The numerical results demonstrated that the variation of fluid temperature with time has a small effect on the bottomhole pressure buildup. The study revealed that an accurate prediction of temperature distributions in the wellbore and in the formation at the moment of shut-in is important for a correct description of the wellbore fluid flow behavior. Introduction Most of pressure buildup tests are performed by shutting in a well at the surface to reduce costs. In this case, at early times the bottomhole pressure response is a result of a dynamic 'interaction between the reservoir and the wellbore Therefore, understanding the physical phenomena occurring in a wellbore is important in the analysis of well tests. Several factors affect the pressure buildup during a well test, namely,afterflowphase redistribution,fluid inertia andheat transfer between the wellbore and the surrounding formation. The first three above mentioned effects have been extensively studied in previous work. However, little information concerning the effect of heat transfer on the bottomhole pressure has been presented. Much of the past work on wellbore heat- transmission has concentrated on the development of methods for predicting the wellbore fluid temperature distribution in producing or injection wells. Most of the reported methods are based on steady-state models of wellbore fluid flow. To determine the formation temperature the transient heat conduction equation is solved analytically or numerically. However, during well testing the wellbore fluid flow is essentially unsteady. Under such circumstances, a steady-state wellbore flow model, which assumes equal flow rates at the inlet and outlet of the well, cannot be used to evaluate the effect of heat transfer on the bottomhole pressure response. The objective of this paper is to improve the understanding the processes occurring in the wellbore during a buildup test by taking into account the heat transfer between the fluid flow and the formation. For this purpose, a numerical model was developed to simulate the two-phase flow and the heat transfer in the wellbore Model validation was carried out through a comparison of computed results with field data. A detailed study was performed to investigate the effect of heat transfer on the bottomhole pressure buildup. Model Formulation The model developed in this paper consists of two parts: a hydrodynamic model and a thermal model. The hydrodynamic model describes the two-phase flow in the wellbore The thermal model simulates the transient heat conduction in the earth. Hydrodynamic Model. A simplified two-phase flow model is used to describe the transient gas-liquid flow in the wellbore.