Analysis of warm-back data after cold-fluid injection into multilayer reservoirs

Document Type

Article

Publication Date

2-1-2020

Abstract

Determining the rate distribution over multilayer injection zones (i.e., injection profiling) is critical to the optimization of injection operations. With the recent advancements in deployment of fiber-optic distributed-temperature-sensing (DTS) technology, temperature data can be achieved at high resolution and at relatively low cost along the wellbore length. During injection of cooler fluids into a higher-temperature injection zone, the temperature at the wellbore and near-wellbore region decreases. During a shut-in period when the injection operation is paused, the temperature at the wellbore sandface and near-wellbore region experiences “warm back” that is caused by the heat flux from the warmer inswept region of the injection zone. A slower warm back is observed for a layer that admits larger amount of cooler fluid during injection. As a result, the sandface warm-back temperature can be analyzed to determine the injection rate per layer, and hence the thermal-front extent per layer. In this work, we develop an analytical model to determine the temporal and spatial temperature variation for a single-phase reservoir during a warm-back period following a constant-rate-injection period. The analytical solution is developed for a single-layer reservoir and extended to multilayer reservoirs. The solution considers heat transfer by conduction and convection during the injection period and conduction during the shut-in warm-back period. The solution is verified by comparison with synthetic numerical-simulation results obtained using a thermally coupled numerical simulator for single-layer and multilayer cases. Graphical interpretation techniques are introduced by recasting the analytical solution into desirable forms. The graphical techniques are applied to synthetic warm-back data to illustrate their application and accuracy in obtaining the injection rate, thermal-front extent, and initial geothermal temperature per each layer.

Publication Source (Journal or Book title)

SPE Reservoir Evaluation and Engineering

First Page

212

Last Page

229

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