Optimum Voidage Replacement Ratio and Operational Practice for Heavy Oil Waterfloods
Bibliographic record
Abstract
Abstract Heavy oil waterfloods have been operating in the petroleum industry for more than fifty years. Over this time, many researchers have tried to identify flood management practices that would optimize recovery from these waterfloods. This multidisciplinary work ties simulation with the evaluation of field statistical results to determine the best operating practices for heavy oil reservoirs that have high permeability thief zones. The particular type of thief zone of concern in Alaskan heavy oil waterfloods is called a Matrix Bypass Event, or MBE. An MBE is a dramatic water breakthrough event in the form of a direct connection between the injector and producer whereby the waterflood process ceases and the injection water cycles directly to the producer without sweeping the matrix. This study evaluates operating strategies for reservoirs where MBEs have developed, taking into account the effects and interdependencies of pre-production, Voidage Replacement Ratio (VRR), and oil viscosity. Evaluation of production from 30 Canadian heavy oil waterfloods indicated that oscillation of the VRR resulted in more oil recovery than a reservoir operated at a constant VRR ~ 1.0. This finding laid the foundation showing that an operational practice called Cyclic Injection/Production would be beneficial, especially for heavy oil waterfloods. Cyclic Injection/Production alternates active injection while production is shut in, followed by active production while injection is shut in. Simulation was performed with a 3-D compositional finite difference reservoir model based on a heavy oil reservoir in Alaska's North Slope. The simulation confirmed that optimal waterflooding practices for heavy oils are significantly different from optimal practices for light oil waterfloods. The best practices also varied according to whether the waterflood had developed an MBE. As long as no MBEs are present and the producers are not bottomhole pressure limited, VRR of less than 1.0 and continuous injection are recommended. For heavy waterfloods that have high perm thief zones, however, Cyclic Injection/Production and a VRR of less than 1.0 improve recovery.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".