CO2 Injection Model Accounts for Joule-Thomson Cooling, Heat Exchange

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 230576, “Joule-Thomson CO2 Cooling Under Different Regime Heating by Adjacent Layers,” by Christina Chesnokov, SPE, University of Adelaide; Rouhi Farajzadeh, SPE, Shell and Delft University of Technology; and Konstantin M. Fedorov, SPE, University of Tyumen, et al. The paper has not been peer-reviewed.

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Heat exchange with surrounding formations and Joule-Thomson (JT) cooling during CO2 injection into deep saline aquifers and depleted hydrocarbon reservoirs can lead to substantial declines in well injectivity. This work introduces an analytical model for nonisothermal CO2 injection that accounts for both JT cooling and interformation heat exchange, assuming that heat transfer begins upon arrival of the temperature front rather than the gas/water front, as adopted in earlier models.

Introduction

Temperature and pressure profiles provide important information about reservoir behavior during CO2 injection. Analytical models can provide such information more quickly with less computational expense. Additionally, the analytical models yield significantly faster inverse solvers, where iterative procedures include forward runs; thus, the inverse solutions for interpretation of laboratory corefloods and improved reservoir characterization from field data are more effective under analytical modeling. Analytical solutions usually regularize the ill-posed inverse problem, resulting in well-posed inverse solutions.

In the current work, an exact solution for a CO2-injection problem is derived wherein the heat exchange with adjacent layers starts at the moment of arrival of the temperature front. The solution accounts for JT effects and nonsteady-state (NSS) heat exchange between the reservoir and semi-infinite adjacent formations. The derived explicit formula allows for the analysis of temporal evolution of temperature profiles. Unlike the steady-state (SS) model, the NSS model reveals no profile stabilization over time. The explicit formulae determine the temperature and pressure profiles at a fixed time, which calculate the path of radial dependency in CO2-/water-phase diagrams; the path connects the well and the reservoir. The analytical model allows for the express method to plot temperature/pressure paths and diagnose hydrate formation. A method of 1D model validation using heat balance in the reservoir while comparing with 2D heat transfer problem has been developed. The method exhibits significantly higher accuracy of the derived analytical model if compared with previous models.

Governing equations for this study are provided in the complete paper, as is a section discussing validation of the analytical model by comparison with 2D heat conductivity.

Sensitivity Study

The sensitivity analysis is performed over parameter ranges selected to capture the physical impact of each dimensionless group. The JT number varies from 10–8 to 10–3, representing changes in the magnitude of JT cooling and its resulting influence on the temperature decline near the injection well. The heat-exchange number spans from 10–4 to 1, reflecting the contribution of NSS heat transfer from the surrounding formations. Across all parameter combinations, the deviation between the reservoir and boundary temperature profiles remains negligible, demonstrating the high accuracy and broad validity of the proposed heat-exchange formulation.