Temperature surveys run during well injection or production can reveal not only intake or production intervals but also the rate of flow. From previous work, the flowrate analysis is based on the "subtangent" or "delta function," which is simply the change in temperature induced by the flow divided by the thermal gradient. This paper investigates accuracy and limitations. of this simplified analysis, and provides design guides for selecting conditions that optimize interpretation. Methods for distinguishing flow-rate changes from changes in formation properties or well radius also are presented.
Diagnostic temperature surveys in wells are at least 60 years old. The earliest use of temperature measurements was primarily for geophysical and geological purposes. For example, determining geothermal gradients, required for regional heat flow studies, was reported by van Orstrand1 and Heald.2 Lithological variations were identified by local departures from the prevailing geothermal profile that were caused by thermal property variations of the formations.3 In the mid-1930's attention turned toward using temperature surveys to diagnose well completion and production problems.4 Deussen and Guyod5 described it technique for determining the position of cement emplacement that relied on the temperature increase caused by heat of hydration. Lost circulation zones were identified as warm or cool temperature anomalies, depending on whether the drilling fluid was hotter or colder than the thieving formation.6 Potential gas production zones were inferred from local anomalies caused by the cooling effect of the depressurized gas as it entered the well.6
More recently attention has focused on the use of temperature surveys to infer flow rate profiles within wells. The methods can be applied to either injection or production wells. For example, in cased wells positions and magnitudes of casing leaks can be identified. In openhole sections the fluid intake or production strata can be located, and the injectivity or productivity of formations can be profiled. In this manner temperature surveys are similar to flowmeter. surveys (e.g., a spinner survey) except that unlike flowmeter surveys temperature surveys can detect flows behind casing7 - e.g., water aquifer flows - and are particularly useful for locating hydraulic fractures.8