ABSTRACT:

Determination of accurate formation temperature is needed for drilling fluid and cement slurry design, determination of geothermal gradients and geothermal reservoir evaluation. Most all known methods to determine the formation temperature are based on shut-in temperature recordings. All these methods require long shut-in periods and result in estimates that are lower than the true reservoir temperature.

A new method has been developed that utilizes temperature recordings from short time flow tests to accurately determine formation temperatures, The temperature distribution prior to production was obtained by solving the diffusivity equation for conductive heat transfer during the circulation period. This provided the initial condition for solving the continuity period. This provided the initial condition for solving the continuity equation for convective heat transfer during production by the method of characteristics. The application of the above solution is shown with a field example.

Introduction

Accurate knowledge of undisturbed formation temperature essential for numerous applications in drilling, completions and production. Applications include 1) drilling fluid and cement slurry design, 2) log interpretation, 3) corrosion in tubing and casings, 4) thermal stress assessment, S) hydrocarbon reserve estimation, and 6) geothermal energy extraction. Accurate assessment of downhole temperatures is required hostile environments, where abnormally high temperatures are encountered in deep and geothermal wells.

The departure from the undisturbed temperature depends upon several factors: original temperature distribution; physic properties of the rock and the fluids; rates of drilling and mud circulation; and casing and cementation of the well. No analytical solution is currently available to estimate the net effect of these factors.

Temperatures recorded in the wellbore can be much lower than the actual formation temperatures (differences of 40 deg. to 60 deg. F are not uncommon). Almost all known methods for determining formation temperatures rely on shut-in temperature recordings. To obtain reliable estimates of static formation temperature most of these methods require a long shut-in period and give estimates that are lower than actual formation period and give estimates that are lower than actual formation temperatures. It is desirable to have accurate estimates in relatively short times, particularly when operating in hostile environments.

The goal of this study is to develop analytical solution describing the temperature distribution during circulation and production and to develop methodology to utilize temperature data from short time flow tests for estimating static formation temperatures.

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