AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Integration of Crosswell Electromagnetic, Geologic, Production and Seismic Data for Characterization, Monitoring and Dynamic Modeling of Water Injection in a Heterogeneous Carbonate Reservoir
(1) ADCO, Abu Dhabi, United Arab Emirates.
(2) Schlumberger, Abu Dhabi, United Arab Emirates.
Crosswell Electromagnetic (EM) tomography is a recently developed technique to map the interwell formation resistivity distribution. In this project, time-lapse crosswell EM surveys are used to monitor saturation changes in a water injection pilot in the basal low-reservoir quality units of a giant carbonate field in the Middle East. We demonstrate how EM results were used with seismic-derived structural information, geological data, structural models, time-lapse cased hole logs, pressure transient and production data to improve reservoir characterization and dynamic modeling.
The evolution of water saturation is derived from measured resistivity distributions, which are obtained by inversion of the EM measurements with respect to an initial resistivity model. To obtain a detailed image of saturation changes, this model must incorporate realistic representations of the small-scale heterogeneities common to carbonate reservoirs. These include layer thickness variations and the presence of thin dense layers interbedded in some reservoir units. Such details allowed improvements in the quality and resolution of the EM results, leading to a better understanding of the reservoir architecture and the behavior of the water flooding process.
Preliminary simulation results using simplified models predicted high vertical sweep across the reservoir units, without encountering any flow barriers. This was inconsistent with the EM results, which show that the injected water stays confined within the lower reservoir units, and the measured injection pressures and flow volumes, which were different from those predicted from simulation. Successive adjustments were therefore applied on the dynamic model to honor the EM and injection pressure results. Adjusting the permeability contrast across some layers prevents the upward movement of the injected water, and is consistent with geological interpretation of continuous stylolitic dense layers within the lower reservoir. In addition, fracture corridors, identified on seismic attributes and supported by PLT data and field-wide review of borehole image logs, are used to account for the injected volume mismatch, yielding the correct injection pressure.
When properly constrained with seismic, geological and production data the EM results provide important information on the location and behavior of the fluid front and identification of the required amount of geological detail that needs to be preserved in the dynamic model.