Optimizing Reservoir Analysis in Complex Transition Carbonate Formation: Insights from Multi-Logging Measurements and Time-Lapse Analysis- A Case Study from Abu Dhabi

Abstract: Formation evaluation in complex transition carbonate reservoirs presents significant challenges due to the heterogeneous nature of the formation and variations in mineralogy, porosity, permeability, and fluid types. In these reservoirs, it is essential to understand the properties of the various rock types and fluids to optimize production and enhance recovery. Time-Lapse Logging While Drilling (LWD) measurements approach was used in this case study to conquer these challenges. To overcome the challenges of presence of multiple rock types with varying porosities, permeabilities and fluids, time-lapse LWD measurements were taken at multiple depths during drilling & after drilling (wipe mode) in different wells across the field. These measurements included resistivity, density, neutron porosity and Nuclear magnetic resonance (NMR), which were used to identify and characterize the different rock types and fluids. The changes in the LWD measurements over time were analyzed to identify fluid movement to improve the understanding of permeability and fluid identification, provide insights into reservoir behavior and enable better decision-making to optimize the completion design. The time-lapse analysis revealed changes in the fluid properties and identified permeability level of the reservoir, which were not observed with the traditional measurement while drilling. This approach takes advantage of the salinity contrast between Water Base Mud (WBM) and formation fluids which leads to changes of fluid properties in invaded zone, such as hydrogen index, density, and resistivity. These changes can be monitored through the measurement of resistivity, density, and neutron porosity and even NMR over time after the invasion of the drilling mud. The use of time-lapse LWD has been particularly useful in areas where there is high uncertainty in water saturation estimates, which is often present across transition intervals. To reduce this uncertainty in petrophysical analysis, Oil Base Mud (OBM) or low salinity WBM must be used while applying this time-lapse approach. Through the analysis of variations in LWD measurements over time, information on rock quality and permeability can be obtained. This approach has also enabled the identification of areas of high productivity, which have been confirmed through production data. Overall, time-lapse LWD analysis provides valuable insights into the dynamics of subsurface reservoirs and has helped to reduce uncertainties in the reservoir model, leading to improved accuracy in production forecasts. The case study presented in this paper demonstrates the effectiveness of the use of a time-lapse of LWD measurements approach in the offshore Abu Dhabi field, where the time-lapse analysis provides a more comprehensive understanding of the reservoir properties and behavior which led to drilling plan, completion design and production strategies optimization.