Steam-assisted gravity drainage (SAGD) methods have proven their effectiveness in economic oil recovery in Alberta and California, frequently achieving a 60% recovery factor. The placement of horizontal laterals within a field and the vertical separation of well pairs (injector and producer) are critical decisions in any SAGD well completion design.
Every SAGD opportunity presents geologists, well planners, and drilling and completion engineers with unique constraints characterized by the various reservoir datasets. Key to gaining the maximum benefit from these data is software tools that integrate and visualize relevant data sources to help reservoir teams correctly interpret subsurface conditions and guide SAGD well completion designs.
Visualization and analysis of reservoir conditions help teams in two specific ways. First, by providing a detailed model of the subsurface environment to aid in well and completion planning. Second, by reviewing the performance of producing wells to determine which SAGD well completion design(s) have worked best for specific geological conditions.
Data-Driven SAGD Well Completion Planning
Relevant data—geologic, petrophysical, simulations, core logs—combined and presented in a 3D visualization environment give reservoir development teams a more detailed and accurate model for planning SAGD well completion. Relevant data that can be integrated, visualized, and analyzed include:
- Core sample data presented in the context of geologic formations to confirm strata and provide information on rock porosity and permeability
- Seismic surveys to provide more accurate estimations of remaining oil in place
- Petrophysical data showing reservoir heterogeneity and a need for flow-control devices to regulate fluid inflow across producing laterals
- Temperature and pressure gradient calculations that provide insight into heavy oil viscosity and guide steam injection strategy
- Reservoir simulation grids that characterize fluid flows and wellbore hydraulics along planned horizontal laterals
Any one of these data sources provides value to the individual specialist on the team, but they provide even greater value when data can be visualized in the context of other relevant reservoir information.
Let Well Performance Guide SAGD Strategy
Reservoir teams can also take advantage of data from producing SAGD wells to understand how completion designs have affected well performance. Decline curves for producing wells can help predict performance for planned SAGD wells with similar geology. Similarly, placement of flow control devices in producing well-pairs can be analyzed to guide optimal placement in a proposed well.
Attributes from simulation grids can be back-interpolated on to the SAGD wells which, when combined with production data, allows detailed comparisons of all SAGD wells either on a well-by-well or cell-by-cell basis. The most successful SAGD well completion designs can be applied to proposed wells with similar geological conditions.
A detailed understanding of the reservoir geology and properties—and insight available through analysis of previous SAGD well completion designs—give drilling and completion engineers greater confidence in developing completion strategies. This level of detail guides:
- Well trajectory and appropriate lateral length to maximize drainage
- Surface and intermediate casing dimensions and cementing methods
- Liner selection to control sand production
- Tubing size to maximize the thermal efficiency during the circulation phase
- Optimal distance of the producer well above oil/water contact in the reservoir
- Location for the sidetrack steam injection well relative to the producer
- Electrical submersible pump (ESP) placement to transport fluid from producer to surface
Heavy oil reservoirs with significant geological heterogeneity will likely require placement of flow control devices (FCDs) to regulate flow across the lateral. Well completion engineers can determine the proper location and type of FCDs that add variable pressure drops to provide a more even distribution of injector steam, improve production, and delay any possible water breakthrough.
CoViz 4D: Insight for SAGD Well Completion Design
One of the most significant challenges to obtaining the maximum value from data sources that characterize reservoir conditions is the integration of the disparate data types and formats. CoViz 4D from Dynamic Graphics, Inc. solves that problem via a data registry that easily incorporates a wide range of datasets acquired or generated by geologists, geophysicists, and drilling and completion engineers. These data are then integrated and presented in a detailed 3D format for analysis that guides development decisions to improve outcomes across all phases of an oil field’s productive life.
CoViz 4D provides all of the capabilities mentioned above regarding integration, visualization, and analysis of data to better understand reservoir conditions and determine SAGD well completion designs. CoViz 4D can further improve a team’s understanding of how past SAGD well completions have affected production. By combining a reservoir’s geological model, wellbore trajectory and completion data, successive reservoir surveys, and production data the evolution of a SAGD well can be animated over time to see how specific design decisions have impacted well production. The capabilities of CoViz 4D can help operators with a SAGD focus achieve greater efficiency in designing well completions that optimize production.
The capabilities of CoViz 4D can help operators with a SAGD focus achieve greater efficiency in designing well completions that optimize production.
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