Mature oil fields that have been previously drilled and produced offer an abundance of data generated over their operational life. This data is of great benefit in analysis and visualization for the purpose of determining viability for secondary recovery efforts. Thus, data integration and visualization software is key in understanding and planning secondary recovery for the most economical returns.
Water Flooding Enhanced Oil Recovery Methods
The earliest form of secondary oil recovery, water flooding is also known as dump flooding to distinguish it from more directed water injection. This technique involves perforating a water-bearing geologic structure above an oil reservoir and letting formation water drain to increase pressure and allow recovery to resume. This approach doesn’t require the construction of additional wells, the transportation of large volumes of injection media to the field, or the construction of additional infrastructure. It has the advantage of lowering the initial capital expenditures needed to produce from a mature oil reservoir which has moved past primary production.
It does, however, have the following disadvantages:
- Whether dump flooding is viable for a field depends on water-bearing geology being fortuitously located.
- The effects of perforating a water-bearing formation can be unpredictable with the potential for the water failing to drain as expected, or pressures failing to rise to needed levels.
- The dynamics of dump flooding are largely out of the operator’s control. Should an unexpected factor alter the dynamics of pressure with the field, options to intervene are few.
The drawbacks versus the potential benefits of dump flooding neatly illustrate the necessity of visualizing reservoir simulation models for secondary oil recovery efforts. The effectiveness of dump flooding is largely determined by the quality of the initial analysis performed on previously accumulated data. Correctly identifying the presence of water-bearing formations in an oil field and completely understanding the hydraulic connectivity of these formations to oil reservoirs—and the connectivity to the strata surrounding both—is vital. The success of a water-flooding operation will be due to how thoroughly the variables are accounted for in initial planning. Errors may not be correctable once the aqueous formation is perforated.
The most effective guard against these errors is to combine all available data into a single visualization environment where all relevant teams working across disciplines can apply their expertise and analysis. This will help determine the most likely result of a dump flooding operation and provide a more accurate picture of its viability before proceeding. The same is true of more controlled secondary oil recovery efforts like water or gas injection.
Secondary Oil Recovery Method: Water Injection
The controlled injection of water is a more commonly used method of secondary oil recovery than dump flooding. In this operation, secondary wells are drilled surrounding production wells, and pressurized water is injected into them. As in dump flooding, this increases the pressure of the reservoirs so that oil recovery returns to volumes that are economically worthwhile. The key difference lies in the control that is exercised over where the water is introduced, the amount introduced, and the pressure and rate it is introduced at. Since water injection is less dependent on existing formations in an oil field, there is a far wider range of oil fields where its use is economically viable.
This versatility comes at a more significant upfront cost. Infrastructure to bring water at volume must be emplaced at the site. A number of injection wells must also be drilled, and proper water injection well design will largely determine the viability of the water injection program. The choice of the injection medium will also play a role. Water is the most common solution, but other mediums like gas can be used. Water can also be modified in some way to better extract oil, or improve its flow toward the production well. Heating the water to reduce oil viscosity in one such technique, and polymers to improve its miscibility with the oil is another option. The layout of injection wells will largely be determined by the geology of the site and the layout of previous production wells, and what injection medium is used will depend on the composition of the oil and the composition of the producing formation. The need to account for these factors before enhanced oil recovery begins further underlines the importance of in-depth analysis of oil field geologic structure and production history before secondary recovery efforts commence.
Utilizing Visualization for Enhanced Oil Recovery
Geomechanical analysis is vital at all phases in the life of a typical oil field. The analysis of the geomechanics of an oil field requires more than a visualization of the latest seismic survey. While this may reveal the presence of certain formations within an oil field, some information about what they may contain can be details that are easily missed. It is only when aspects such as pressure, reservoir deformation, and other in-situ stresses are modeled over time that variables such as hydraulic connectivity and velocity changes can be determined with clarity, or project with a degree of certainty how any secondary oil recovery efforts will change them. Combining historical production data, structural, stratigraphic, and seismic mapping can reveal:
- oil reservoirs that may have been bypassed in previous production periods through misidentification, or lack of economic viability at the time
- untapped layers or zones in previously productive multi-layered reservoirs
- a comparative basis against the production histories of nearby fields by which positive productivity enhancements applied can be further improved
The critical factor is that when these are mapped over time, the existence of variables can be definitively proven or disproven, reducing the uncertainty surrounding injection or drilling production wells. An example would be the drilling of a production well causing a decrease in not only the targeted reservoir but a neighboring one as well—proving connectivity between the wells. How this aspect has changed over time further refines this information as a history of production from multiple wells compared side by side can reveal vital information. Unanticipated pressure losses from the beginning of production may reveal that these reservoirs were always connected. Pressure changes occurring later can reveal that primary production drilling, or water injection wells created a connection by altering a geological formation.
The critical factor is that when these are mapped over time, the existence of variables can be definitively proven or disproven, reducing the uncertainty surrounding injection or drilling production wells.
In either example, knowledge of this connection will affect secondary oil recovery efforts. Its exact nature needs to be known when developing production plans, and this resolution of granular knowledge can only be achieved when all behavior of forces in an oil field are viewed over time. Reservoir interdependence can only be clearly interpreted when all information is consolidated in a centralized software package that intuitively supports the needs of all related disciplines needed in geomechanical analysis.