Interpretation of Temperature Profiles in Water-Injection Wells
Authors: Smith R.C. , Steffensen R.J. 
Published: December 2007

Using a mathematical model, wellbore temperature behavior is studied for a wide variety of water-injection conditions. Guidelines presented for interpreting injection-well temperature logs significantly aid in analyzing conformance by injected water.

Introduction
Wellbore temperature behavior has been studied using a mathematical model for a wide variety of water-injection conditions to improve understanding and interpretation of temperature logs in these wells. Computed shut-in temperature profiles are presented for key situations to provide insight about how these situations influence shut-in temperatures. This information will significantly aid in analyzing conformance by injected water. Suggested procedures for log quality control and timing of surveys are also discussed.

Temperature Behavior in Water-Injection Wells
A qualitative review of temperature behavior in water-injection wells is presented to aid understanding of the following material. The curves in Figs. 1 through 3 qualitatively show the effects of injection rate, surface water temperature, and shut-in time on down-hole temperature profiles.

Effect of Injection Rate on Injection Temperature Profiles
Consider first how the injection rate of the water and its surface temperature affect the temperature behavior in the wellbore. Fig. 1 shows temperature profiles for injection at the same surface temperature but at different rates. The right-hand curve of Fig. 1 shows the original temperature condition before injecting water (the geothermal temperature profile). Although the profile is roughly linear with depth, its slope varies with geographic location and rock type.The left-hand curve of Fig. 1 shows the temperature profile for an extremely high (infinite) injection rate. For this case, the injected fluid would have little time to exchange heat with the formation while moving down the wellbore. Thus, the resultant temperature curve would be essentially a straight vertical line. For injection at lower rates, the water does have time to gain heat as it moves down hole. At normal surface temperatures of the injection water, it follows that every injection rate between zero and infinity would produce an injection temperature profile with a gradient somewhere between these two extreme curves, as shown by the center profile of Fig. 1. As the water enters warmer regions, it absorbs heat and its temperature increases. with depth. When the water reaches the top of the zone, taking fluid at Point a, the formation takes on the temperature of the injected water. Therefore, the water that passes on down the hole across the injection zone changes very little in temperature. The injection temperature curve becomes essentially vertical across the injection zone, as indicated from Point a to Point b in Fig. 1. Below the lowest injection interval, the injection temperature curve shifts rapidly toward the geothermal temperature curve.

Effect of Surface Temperature on Injection Temperature Profiles
The surface temperature of the water also influences the injection curves. Three curves are shown in Fig. 2 for the same rate at different surface temperatures.
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