Layer-resolved injection allocation from impulse warmback testing using zone-integrated temperature derivatives

Abstract Accurate knowledge of how injected fluid distributes across reservoir sublayers is essential for waterflooding, enhanced oil recovery, geological CO₂ storage, geothermal, and underground gas storage operations. Existing analytical warmback methods require controlled injection conditions and knowledge of the geothermal temperature profile, both of which are difficult to ensure in field applications. This paper introduces a zone-integrated distributed temperature sensing (DTS) warmback diagnostic based on impulse injection that removes the dependence on prior injection history and the undisturbed geothermal temperature profile. The cold injection is limited to a brief slug, so that the shut-in temperature response reduces to a closed-form analytical solution governed by only two injection parameters: total injected volume and its volume-weighted average temperature. The log-derivative of the depth-integrated DTS temperature signal, S' i = t dS i /dt , exhibits a characteristic peak time, t rad, i $$\:,$$ that is proportional to the injected volume entering i th sublayer. The injection fraction can then be estimated from the relative t rad, i values, with sublayer thickness and thermal conductivity included explicitly. A slope of -1 on the S' i log-log plot identifies the radial-conduction regime and provides the valid analysis window. The method is validated using CMG-STARS numerical simulations across three cases of increasing complexity, demonstrating accuracy and robustness across heterogeneous reservoirs and variable injection temperature conditions.