Miscible Gas Injection Tests in Carbonates and its Impact on Field Development

Abstract

Abstract Considerations for better ultimate oil recovery and maintaining plateau production beyond the current expectations depend on appropriate EOR methods. Laboratory core floods provide both the recovery characteristics and validity of the microscopic displacements in 1D, and hence the confidence in the choice for macroscopic simulations models and field development options. Laboratory core floods are typically conducted on long composite of stacked cores to assure good miscibility, minimize experimental uncertainties, and ensure representative reservoir conditions are replicated. This study chose to investigate six miscible gas process displacements on a long composite core of a prolific Cretaceous zone of a giant carbonate reservoir. The displacements were designed to mimic the reservoir advance rates at full reservoir conditions under both conventional vertical floods as well as the challenging horizontal injections. We examine the miscible fluid injection and hydrocarbon recoveries of three fluid systems in tertiary mode, i.e. following a secondary water flood. The injection schemes comprise, a tertiary hydrocarbon gas, a tertiary hydrocarbon / brine WAG and a continuous CO2 gas all at miscible conditions. The miscible gas injection tests, within the experimental limitations provided recovery profiles and gas process injection characteristics to validate model predictions, and thus enhance confidence in pilot as well as full field development studies based on the underlying reservoir simulation models. Our work highlighted the excellent choice of CO2 as a miscible gas fluid, and dispelled gross uncertainties in conducting such tests in either horizontal or vertical modes. The repeatability of six different secondary water floods confirmed the robust test design, and confidence in the tertiary gas injection measurements.