Identification of Environmental Effects of Acid Gas Injection Using X-Ray Computed Tomography
Bibliographic record
Abstract
Abstract With the increasing trend to dispose acid gases (H2S and CO2) generated from natural gas processing, by geologic sequestration, industry and government must carefully assess the compatibility of the rock formation and fluids with the intended injection stream to ensure safe and efficient facility operations. Recent geochemical analysis of carbonate cores, previously subjected to acid gas core displacement tests, prompted an examination of changes to porosity using x-ray computed tomography (CT). Results indicate that increases in porosity may be linked with the increases in permeability observed during the core injectivity testing. Visually distinct areas in the core suggested that changes were non-uniform implying regions of higher consolidation representing lower permeability. In addition, when several voids were subjected to detailed CT image analysis, we observed traces of halite (NaCl) crystals probably resulting from the desiccation of formation water by the extremely dry acid gases. This suggests that the increase in porosity could not be attributed to dissolution processes, but due to fine dislodgement of materials during the high pressure injection. Inadvertently, the permeability increases were resultant of both desiccation effects and particle dislodgement. Introduction Acid gas injection has been accepted as a practical way to dispose of the undesirable H2S and CO2 (acid gases) produced from natural gas processing. This technology allows the production of sour gas reservoirs to be economically viable and provides an environmentally friendlier option in comparison to other disposal alternatives. In order to successfully dispose of the acid gas in a safe and efficient manner, the process of selecting an adequate disposal formation includes assessment of various reservoir conditions in order to determine suitability. One of the requirements is to examine the compatibility of the mineralogy of rock formation and its fluid with the injection stream, usually accomplished through core sensitivity tests. Core Sensitivity Tests The objective of the core sensitivity test is to observe any significant changes in permeability, to ensure that impairment to injection will be minimized. This test is essential because of the potential to damage the formation as a result of the acid gas injection which could jeopardize injection or containment within the formation. Some potential formation effects which may include but is not limited to; desiccation, dissolution and dislodgement of fine materials (1). Desiccation occurs when the formation fluid has significant salinity and the acid gas stream is highly understaturated in water resulting in a salting out effect as the injected stream reduces the initial brackish pore fluids. Dissolution takes place when acid gases dissociate in formation fluids decreasing the pH and increasing the natural water-rock reactions of the reservoir. Fine dislodgement is generally experienced in poorly consolidated cores when subjected to the injection pressures and increased flow rates over the small surface area of the pores. An ideal core would be sufficient in size to allow for monitoring of all of these effects, especially the geochemical effects of dissolution and re-precipitation, if they occur (1). Unfortunately, in practical applications the selection of cores to choose from is limited when using a previously producing well to inject into a depleted hydrocarbon reservoir.
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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".