Buildup Evaluation of an Overpressured Naturally Fractured Carbonate
Bibliographic record
Abstract
Abstract This paper examines the buildup pressure response of a well that penetrates an unconventional tight naturally fractured carbonate reservoir in Mexico. Four buildups in the same well over a period of 4 months, with intermediate flow periods, suggest partial closure of natural fractures. Radial flow is dominant in the four buildups. This is recognized in semilogarithmic and pressure derivative cross plots. However, the formulations require a consistent empirical component to match the buildup data. The four buildup tests are evaluated with a semi-empirical dual-porosity model with restricted interporosity flow. The restricted flow between matrix and fractures is the result of partial secondary mineralization (cementation) within the fractures, which can be visualized as a natural positive skin that reduces the oil flow from the matrix to the fractures. The empirical part of the method is provided by a severity exponent (SE), which helps improving the match of the buildup semilog and derivative plots. The buildup evaluations permit estimating several parameters of interest, including fracture capacity (k2.h), skin, storativity ratio (ω), and the extrapolated pressure (p*). The calculated k2.h is equal to 8.73 md-ft during the first and second buildups, 8.34 md-ft during the third buildup and 5.5 md-ft during the last buildup, which is also the longest (118 hours). Results suggest that although natural fractures are present, they tend to close once the well goes on production. Thus, the conclusion is reached that the carbonate reservoir is tight and likely stress dependent. The values of skin tend to increase going from −2.51 to −2.20 to −1.45 to +0.46 indicating that the reservoir goes from improved condition around the wellbore to slightly damaged conditions probably due to fracture closure. On the other hand, ω increases continuously going from 0.46 to 0.56 to 0.66 to 0.71 suggesting a tendency of the reservoir to move from dual to single porosity behavior. The reservoir is overpressured (0.87 psi/ft) and the extrapolated pressures (p*) decrease from 18,200 to 18,050 to 16,700 to 14,000 psi because of the tight characteristics of the reservoir. However, given the large size of the reservoir, the likelihood of depletion is unlikely. The novelty of this study is the development of a new easy-to-use semi-empirical well testing model for matching the buildup pressure response of four tests performed in a well that penetrates an overpressured, unconventional, tight naturally fractured carbonate. The tests could not be matched with well-known commercial packages.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 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".