Detection Injection Zones in Carbonate Reservoir by Integration Production Log with Borehole Image Data at Horizontal Wells

Abstract

The Mid-Cretaceous Formation is a significant carbonate reservoir primarily located in the Middle East, notably in Iraq, Iran, and parts of the Arabian Gulf. It dates from the Late Cenomanian to Early Turonian period (94–90 million years ago). The formation comprises diverse lithologies, including bioclastic and rudist-rich limestone, grey-white limestone, foraminiferal-rich facies, and limonitic limestone. This study investigates the relationship between open-hole log data and dynamic injection data. The PoreSpect technique assumes that resistivity data from electrical borehole images reflect the flushed zone around the borehole. These electrical images, acquired using the Full-bore Formation MicroImager (FMI*), are calibrated with shallow resistivity and log-derived porosity to produce an effective porosity map. The underlying principle is that the FMI images provide a conductivity map of the borehole wall, which can be converted into porosity values using Archie’s equation for the flushed zone. Image log interpretation provides valuable insights into porosity types and distributions. Primary porosity is associated with depositional processes, while secondary porosity—such as fractures and vugs—is developed through diagenetic alterations and is typically irregular in nature. This study focuses on the behaviour of the injection profile along the lateral section of horizontal wells, using image-derived porosity and logging-while-drilling density data. The findings reveal two distinct porosity groups. The first group, characterized by high secondary porosity (greater than 5%), accounts for over 90% of the injected water. The second group, despite having good total porosity, shows low secondary porosity and accommodates less than 10% of the injected water. A strong correlation exists between secondary porosity distribution and the injection profile, where zones with higher secondary porosity exhibit higher injectivity. Conversely, zones with high resistivity are associated with low injectivity and minimal secondary porosity. The approach presented in this study enhances the understanding of how different forms of carbonate porosity influence injection behaviour. The results confirm that secondary porosity plays a more significant role in injectivity than primary porosity. Although limited by the availability of horizontal production logging tool (PLT) data in injector wells, the analysis provides meaningful insights into injection performance. These findings are essential for optimizing well completions, hydraulic fracture stage design, packer and inflow control device placement, and overall reservoir management strategies.