Streamline Technology for the Evaluation of Full Field Compositional Processes; Midale, A Case Study
- Robert A. McKishnie (Epic Consulting Services Ltd.) | Shelin Chugh (Epic Consulting Services Ltd.) | Sonja Malik (Enerplus Resources Fund) | Robert G. Lavoie (CalPetra Research & Consulting) | Paul J. Griffith (Apache Corp.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- October 2005
- Document Type
- Journal Paper
- 404 - 417
- 2005. Society of Petroleum Engineers
- 5.5.8 History Matching, 5.1.5 Geologic Modeling, 4.2 Pipelines, Flowlines and Risers, 5.4.1 Waterflooding, 5.4.9 Miscible Methods, 1.6 Drilling Operations, 5.3.2 Multiphase Flow, 5.4 Enhanced Recovery, 4.3.3 Aspaltenes, 5.5.3 Scaling Methods, 4.6 Natural Gas, 5.1.1 Exploration, Development, Structural Geology, 4.3.4 Scale, 5.7.2 Recovery Factors, 5.8.6 Naturally Fractured Reservoir, 5.2.1 Phase Behavior and PVT Measurements, 5.1 Reservoir Characterisation, 5.5.7 Streamline Simulation, 5.5 Reservoir Simulation, 5.4.2 Gas Injection Methods, 5.3.4 Reduction of Residual Oil Saturation
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Traditionally, the evaluation of CO2-flooding processes is performed withfinite-difference compositional-simulation models. However, compositionalsimulation is impractical for modeling large-scale CO2 floods because ofcomputational run-time restrictions. In cases in which reservoir heterogeneityand fluid mobility dominate the reservoir recovery mechanism, streamlinesimulation offers a viable alternative to compositional simulation. The"reduced" physics in streamline simulation allows field-scale CO2-floodmodeling to be feasible, as long as the streamline pressure/volume/ temperature(PVT) model can be calibrated so that the streamline model will produceaccurate results for CO2-injection processes. Using streamline simulationallows for the evaluation of multiple full-field development scenarios thatotherwise would not be possible with compositional simulation.
The objective of the study was to provide CO2-flood performance forecastsunder various full-field development scenarios for the Midale field. This paperfocuses on the methodology and results from the 1,000-well,>400,000-gridblock, 45+-year streamline simulation of the Midale field. Inparticular, it discusses the construction and history match of the full-fieldmodel, the calibration of the streamline model with the compositional model,and the development of the full-field CO2 forecasts.
The Midale field, in southeast Saskatchewan, Canada (Fig. 1), was discoveredin 1953 and subsequently delineated on 80-acre spacing. The field producedunder competitive drainage until unitization in late 1962, after which aninverted nine-spot waterflood scheme was implemented. During the mid-1980s, anextensive vertical infill program was used to modify the waterflood patterns.Horizontal wells in the late 1980s and multilegged perpendicular horizontals inthe mid-1990s were used to further improve waterflood conformance. To date, theunit has recovered more than 125 million STB of oil (primarily from waterfloodoperations), representing approximately 24% original oil in place (OOIP).
Recognizing the large volume of oil that would not be recovered bywaterflooding operations, a CO2-flood pilot project was initiated in 1984. Thisproject involved the drilling of 10 closely spaced wells in an area 4.4 acresin size and generated an enormous amount of reservoir and geologicalinformation. Results from the CO2 pilot project were used to justify thelarger-scale Midale CO2-flood demonstration project, a six-pattern CO2 floodlocated in the southwestern part of the unit that began operations in 1992.Positive results from the Midale CO2 demonstration project were instrumental injustifying the neighboring Weyburn CO2-flood project, which began operations in2000, and they were also key to the technical justification of a full-fieldMidale CO2 flood.
Apache's acquisition of the field in 2000 was followed by an aggressivecampaign to increase the recovery through infill drilling with horizontal wellsat 20- to 40-acre spacing, increased injection and throughput (by a factor ofthree), and a review of the feasibility of a full-field CO2 flood.
The objective of this study was to assess the commercial CO2-flood potentialof the Midale unit within a 5-month study period. Traditionally, acompositional simulator is used to accurately model the pressure-dependentphase behavior of CO2. However, despite advances in computing power andsoftware, compositional simulation is impractical for field-level simulationsof large fields such as the Midale unit. An alternative to compositionalmodeling is streamline simulation. Recent advances in streamline simulationshow that in cases in which reservoir heterogeneity and theproduction/injection coupling dominate, first-order approximations offered bystreamline simulation are sufficient for full-field development decisions.Invariably, the development plan is modified as the field is depleted and moreinformation becomes available. Also, full-field streamline simulation allowsfor optimization of water-alternating-gas (WAG) cycles and pattern-injectiontiming that would be difficult to evaluate with compositional simulation. Thedifficulty with streamline simulation is that it lacks the direct PVT model toaccurately describe the interaction between the oil and the CO2 at variouspressures and temperatures. Detailed compositional models are required whendrastic changes in fluid properties occur, such as near the critical point orcondensate dropout in retrograde gas reservoirs. When the problem is one ofmodeling a relatively smooth transition between miscibility and immiscibilityat a certain pressure, the modification of a black-oil model by Todd andLongstaff is quite often used because of its significantly faster computationalspeed.
|File Size||7 MB||Number of Pages||14|
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