Study of Hydrated Clay Reactions to Various Cations Using Low-Field NMR
Bibliographic record
Abstract
Abstract Low-field NMR has been used in downhole logging tools for fluid and petrophysical evaluation of many petroleum reservoirs. In heavy oil and oil sand formation evaluation, clays have a signature response to low field NMR, that is similar to that of oil. A further study of clays alone is the key to evaluate and to better understand clay-water interactions in a fast and non-destructive way. Clays can be found throughout many sectors of the petroleum industry. From reservoir evaluation to environmental pollution, clays are known to have swelling properties that can pose problems including plugging of pore throats within the reservoir or possible lateral movement of contaminants on the surface. This paper is part of a larger study on clay characterization with low-field NMR. Of particular interest in this study is the interaction of clays with high salinity brines. Clays are typically surrounded by ionequilibrated water prior to exposure to high cation-content brines. In this study, four types of clays are used: kaolinite, illite, calcium-montmorillonite and sodium-montmorillonite. The clays are initially hydrated with distilled water and are then exposed to varying cation solutions. The cations used are Na+, Ca2+ and Mg2+, which are readily found in formation brines. NMR spectra of clays exposed to brines tend to show distinct characteristics of both amplitude and mean relaxation. Analysis of the NMR spectra correlates the NMR response to clay-chemistry of the individual clays. Introduction Low Field Nuclear Magnetic Resonance (NMR) has been utilized throughout the petroleum industry to evaluate and characterize many petroleum reservoirs. This technique has been successful in discriminating between oil and water, quantifying the fluids within a porous medium, as well as the amount of mobile and immobile fluids. The principles of this technique have been extensively published elsewhere1, 2 and will not be repeated here. The presented work deals with the interpretation of NMR spectra of clay/water and clay brine mixtures. The spectra are generated through the CPMG pulse sequence and correspond to the inverted decay curves of transverse relaxation1, 2. The ability to determine clay bound water has been studied for many years. Several researchers have undertaken rigorous lab experiments to study the clay-bound water (CBW) in NMR, as the responses are similar to that of heavy oil and oil sand evaluation. Prammer et al.3 conducted field and laboratory experiments on clays that were exposed to synthetic brine samples resembling that of seawater and put through a press to remove excess water. The authors concluded that the clay mineralogy had little influence on where CBW volumes lie but had significance in the surface-to-volume ratio, which is an indicator of the cation exchange capacity (CEC). Also, based on the field and laboratory data, the relaxation time for CBW lies in the 1ms range. Straley et al.4 evaluated cores for porosity, pore size distributions, free-fluid porosity, clay-bound water, permeability, oil viscosity and oil saturation.
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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) | 0.001 | 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 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".