Structure and property models with well logs and flowback tracer towers. Note the rock heterogeneity in the top layer that’s common in carbonate reservoirs. Data courtesy of Rocky Mountain Oilfield Technology Center and USDOE.
Carbonate reservoirs are the source of some of the world’s largest oil and gas reserves. These reservoirs are mostly known for their heterogeneous formation and are more complex to characterize. This complexity is mostly due to the variable distribution of porosity and permeability in carbonate rocks. This porosity and permeability can expand in both horizontal and vertical directions across the stratigraphic boundaries and sub-facies. This distribution makes the production estimation through such reservoirs a challenge.
A 3D permeability model is thus a very crucial method in characterizing a carbonate reservoir. Engineers and geoscientists can use the model to efficiently target the high permeability reservoir and avoid low permeability reservoir for better hydrocarbon and economic yield.
Understanding Permeability in Carbonate Reservoir
Permeability defines the ability of the rock to allow the movement of fluid through it. In a carbonate reservoir, permeability distribution has a high degree of variability. This variability in porosity and permeability can be defined by grain size, lithofacies, clay content, and fractures in the subsurface rock structure. The primary production, in an individual well, is often directly proportional to the permeability found in the reservoir penetrated by the well. Thus, the permeability data obtained from one well cannot be reflective of the permeability of the entire oil field. The production process can show extreme variations among adjacent wells resulting from variations that may include a primary fine granular, low porosity characteristics, as well as a secondary karsting cavernous, high porosity characteristics. The ability to create a 3D model and visualize these variations can be highly beneficial for effective decision making.
The data for efficient carbonate reservoir characterization can be obtained through various methods including seismic surveys, geological modeling, and well logging methods. A geological conceptual model of the carbonate reservoir can be achieved with the integration of this wide range of diverse geological and petrophysical data in a single platform. This allows engineers and geoscientists to visualize porosity and permeability and get a better understanding of the variability, complexity, and productivity of the carbonate reservoir. Analysis of these data helps them make an informed decision on drilling and recovery strategy from such complex reservoirs.
Leveraging 3D Permeability Modeling
Accurate 3D modeling of the reservoir permeability can be important in the economic development of an asset as it reduces the risk of drilling into a low permeability reservoir. Geologists, petrophysicists, geophysicists, drilling engineers, and reservoir engineers can benefit from 3D permeability modeling in the following ways:
- Minimize uncertainty regarding carbonate reservoir characteristics with the integration of diverse data
- Study subsurface lithology along diagenetic facies to determine porosity and permeability distribution
- Use geologic, seismic, and log data to determine well to well heterogeneity and permeability to minimize uncertainty.
- Determine the heterogeneity of the subsurface by integrating well log data with the geological conceptual model
- Identify and locate potential karst reservoirs
- Determine high permeability “pay zone” for making drilling and recovery related decisions
These decisions are supported by the ability to integrate and visualize multi-dimensional datasets in a single platform with a tool like Coviz 4D. It allows the asset teams to integrate different format datasets and visualize them to derive a coherent interpretation.
CoViz 4D for Permeability Modeling in Carbonate Reservoir
CoViz 4D is an ideal platform to effectively incorporate the multi-disciplinary data and fully visualize it in a single geospatial volume. With 3D modeling, variability, as well as correlation among primary and secondary permeability networks, can be determined in carbonate reservoirs. With integration and modeling, asset teams are able to make efficient design and recovery-related decisions.