Computer Study of Factors Affecting Temperature Profiles in Water Injection Wells

Abstract

The computer study described here defines the main factors affecting temperature surveys in water injection wells, making possible a more accurate interpretation of these surveys. An important conclusion is that differential temperature curves are not applicable to the quantitative determination of water injection profiles. Introduction A computer study has been made of temperature behavior in and near water injection wells to improve understanding and interpretation of temperature logs in these wells. Validity of the computer model was tested by comparing computed and field-measured temperatures. Good comparisons were obtained for two West Texas water injection wells. Thus the factors affecting these temperature curves can be stated with confidence. The location of zones taking water, the determination of distribution of the injected water among the zones, the detection of channeling, etc., are fundamental to waterflood management. Radioactive-tracer surveys and, to some extent, down-hole flow meters have been used for these purposes. With an increase in the number of injection wells, there is incentive for better and more economical methods to obtain this information. Interest in well temperature surveys for this purpose has increased recently, spurred by two factors. First, absolute temperature surveys can be more economical than radioactive-tracer surveys economical enough to justify more surveying, enabling more thorough early analysis and follow-up of injection well conditions. Second, the radius of investigation by temperature surveys exceeds that for tracer surveys. Tracer surveys are limited to analysis of wellbore conditions. In contrast, the temperature profile in effect sees beyond the wellbore, since it is influenced by conditions a few feet radially from the well. The usefulness of temperature-profile measurements in wells was indicated as early as 1940 by Millikan. Guyod's discussion in 1946 of wellbore temperatures under static and producing conditions contributed to the understanding of temperature behavior. A very significant contribution to the understanding of temperature profiles in water injection wells was made by Nowak in 1953. His work dealt primarily with quantitative interpretation of absolute temperature profiles after shut-in. In 1954, Bird presented a quantitative interpretation of the injection absolute temperature profile. Several other authors have also discussed the profile. Several other authors have also discussed the interpretation of temperature profiles, providing numerous field examples. The interpretation of temperature profiles still is, of necessity, part art and part science. The shut-in temperature curves of Fig. 1 show several temperature anomalies. It is these anomalies or temperature contrasts between various vertical intervals that are informative. They permit interpretations of what has occurred down-hole. However, there have been doubts about the qualitative and quantitative validity of injection profiles determined from temperature surveys. Therefore, a need was felt for a computer study considering as thoroughly as possible the main factors affecting temperature behavior in water injection wells. The approach in studying temperature profiles was to develop a two-dimensional (radial and vertical) mathematical model to simulate heat flow in the wellbore and surrounding region. JPT P. 1447