Carbonate reservoirs contain a majority of the world’s petroleum reserves, and they are one of the more challenging geologic formations to characterize. Within these reservoirs, porosity and permeability can be highly complex and vary widely with little spatial correlation. Initial and secondary porosities can range from low porosity intergranular/inter-crystalline primary to cavernous karst secondary (very high) porosities. Those ranges present a major challenge when looking for bypassed pay and determining the best methods for enhanced oil recovery (EOR).
An EOR method that works well for one well may not work on a nearby well but could be effective for a distant well. Given these challenges, reservoir teams can more easily plan and manage enhanced oil recovery activities with the aid of software that visualizes porosity and permeability variations throughout a reservoir—along with other key reservoir attributes.
Better Understanding of Variability Within a Carbonate Reservoir
Given the extreme heterogeneity of porosity across many carbonate reservoirs, the more data available to geologists, geophysicists, petrophysicists, and reservoir engineers the better their understanding of reservoir complexity and their ability to determine the optimum EOR methods.
Software tools like CoViz 4D excel in the ability to easily integrate a wide range of reservoir data and present the data as a detailed 3D reservoir model to aid in reservoir analysis, development, and monitoring. With regard to EOR activities, CoViz 4D facilitates a better understanding and analysis of the heterogeneity and factors that influence development decisions in the following ways:
- Integrate seismic, geologic, and petrophysical data into a single, detailed reservoir model to show its complex geophysical heterogeneity
- Correlate production data with seismic data to quickly identify karst/cave areas that have been reached as well as others that have been bypassed
- Combine well log data with geologic models to provide greater accuracy regarding rock heterogeneity surrounding wells and help determine appropriate enhancement methods
- Locate existing wells, producing and depleted, to plan locations and trajectories for EOR injection wells
Structure and property models with well logs and flowback tracer towers. Note the rock heterogeneity in the top k layer that’s common in carbonate reservoirs. Data courtesy Rocky Mountain Oilfield Technology Center and USDOE.
With this level of information and the ability to visually explore a carbonate reservoir, engineers can identify the areas that present the greatest potential for EOR and determine the best recovery methods based on porosity and permeability properties.
Monitor Enhanced Recovery in Carbonate Reservoirs
In addition to helping reservoir engineers understand and identify EOR opportunities in carbonate reservoirs, CoViz 4D can help monitor the EOR activities, allowing production teams to assess recovery effectiveness.
- Monitor developing fracture conductivity using microseismic data, if acid fracking is selected as the EOR method.
- Compare volumes and pressure of injected water, steam, or CO2 against well production volumes to gauge recovery effectiveness.
- Use temperature observation well data to show the extent of the steam chest to gauge the progress of their enhanced oil recovery methods.
- Track tracer data to alert to any unintended inter-well movement of injected fluids.
Single time-step image showing vectors of tracer direction and microseismic data within a heterogenous limestone/sandstone reservoir. Production towers also shown. Data courtesy Rocky Mountain Oilfield Technology Center and USDOE.
By visualizing EOR activities in the context of a reservoir’s porosity and permeability, production teams gain the most accurate understanding of where EOR methods are being applied and the effectiveness of the recovery techniques. The ability to carefully monitor production allows reservoir engineers to quickly respond to changing conditions, identify the causes, and implement mitigation strategies to improve recovery.
To further help reservoir engineers understand the efficacy of their EOR strategies, CoViz 4D integrates time-series data (4D) associated with seismic studies, property grids, well status, injection volumes, and production data. CoViz 4D then animates these data to help reservoir engineers more clearly understand the interdependencies of these factors, the EOR methods, and their effect on enhanced oil recovery.
CoViz 4D for Better Enhanced Recovery in Carbonate Reservoirs
Research has shown that historically more than 50% of the oil that could be recovered by waterflooding EOR isn’t touched and remains in a carbonate reservoir. A multidisciplinary approach to analyzing carbonate reservoirs using the wealth of subsurface data is enabling development teams to more efficiently and effectively locate volumes of unswept oil and determine the optimum enhanced oil recovery methods.
Lead image courtesy of Shutterstock