Abstract

Interpretation of temperature logs has been done successfully in wells to identify water or gas entries location, detect casing leaks, and evaluate cement placement. This paper shows how knowledge of the Joule-Thomson cooling effect and frictional heating effect can be applied for well test interpretation.

Many analysts rely on pressure derivative curve to diagnose wellbore storage period and radial flow regime on pressure transient data. However, there are field examples that flow regimes can't be accurately determined.

During transient tests, both pressure and temperature are changed depending on downhole flow rate. In gas producing wells, Joule-Thomson cooling and frictional heating effects are the main dynamic factors causing flowing bottomhole temperature to differ from the static formation temperature at that depth. When a gas well is shut in, JT cooling effect is vanished and this causes a sharp increase in sandface temperature. As effect of WBS ends, wellbore temperature gradually cools down due to heat conduction with near wellbore region.

This paper demonstrates a new technique for determining end of wellbore storage in pressure build-up tests for gas producing wells using temperature transient data. Application of this robust technique was demonstrated using three gas wells in which both temperature and pressure transient data were analyzed for more accurate welltest interpretation.

Introduction

In pressure transient tests [1], the early portion of the well test data is usually affected by the wellbore storage effect and might be influenced by skin[2] and reservoir permeability.

The wellbore storage effect delays the formation pressure response and distorts the early portion of pressure transient data. Diagnosing of the radial-flow regime is crucial to quantitative interpretation since it provides values for permeability and skin. Unit slope and the plateau on the pressure derivative curve as well as Horner plot are usually used to identify pure wellbore storage and radial flow regime as shown in Fig.1. The interpreter's first task always is to identify the unit slope line and derivative plateau to identify flow regimes [3].

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