Structural Integrity of Casing and Cement Annulus in a Thermal Well Under Steam Stimulation
Bibliographic record
Abstract
Abstract Steam stimulation is one of the viable methods in extracting heavy oil from oil sand reservoirs. In this thermal process, the injection well is subjected to high temperature. Numerical simulations were used to investigate the structural integrity of the well under such high temperature environment. In this study, stresses in the metal casing, cement annulus and surrounding shale formation were examined in detail to evaluate if the induced stresses exceed the material strengths under varying boundary conditions. These include the effect of heating rate, poor cement, and shale formation properties. Introduction In Alberta, thousands of deviated wells have been drilled through shale formation to extract heavy oil from underneath oil sand formation using thermal recovery processes. Thermal deviated wells in shale impose more technical challenges than conventional wells in consolidated rock because of their unique features. Thermal recovery processes such as steam assisted gravity drainage and cyclic steam stimulation, involve high temperature operation up to 300 ° C. Shales found in Alberta are compaction type without strong cementation, and have been well known to swell and lose its structural integrity upon exposure to water based fluid. Occurrence of casing impairment and failure in shale formation after years of service are frequent. A completed deviated well is made up of a series of annular rings of steel casing, oil well cement and shale of varying thickness. There are differences in mechanical, hydraulic and thermal properties among these materials. The overall response of a thermal well subject to heating is governed by not only each material, but also the properties of interfacial steel-cement and cement-shale interaction. Material properties of steel, oil well cement and shale have been well studied separately. However, the behaviour of steel-cement and cement-shale interfaces have not been received much attention because the interaction behaviour is very complex, dependent on the imposed boundary conditions. In a well completion, a borehole is drilled and advanced with drilling mud. Then, steel casings are inserted into the drilled hole filled with mud. The mud in the annular space between the steel casing and the drilled hole is removed by a clear wash or spacer fluid, followed by the cement slurry. In idealized situation, all drilling mud should be removed and the annular space should be filled with cement slurry. However, the complete displacement of drilling mud by the spacer fluid and cement slurry may not be achieved. There leaves a residual mud layer adhered to the inside and outside surfaces of borehole and casing, respectively. The thickness of this layer depends on the displacement processes (fluid velocity and annular space) andfluid rheology and density. Undesired mixing can be induced because there are differences in fluid rheology and density of rilling mud, washer fluid and cement slurry (non-Newtonian fluids). Local channel or fingering could occur in narrow spaces since the fluid displacement takes place in a narrow eccentric annular configuration bounded by the circumferential surfaces of the drilled well and the steel casing 1. Imperfect oil well cementing could produce weak and non-homogeneous cementituous material in the cement annulus.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".