CONTROLS ON RESERVOIR DIAGENESIS IN THE LOWER GORU SANDSTONE FORMATION, LOWER INDUS BASIN, PAKISTAN
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Bibliographic record
Abstract
Sandstones in the Lower Cretaceous Lower Goru Formation in the Lower Indus Basin, Pakistan, are important reservoir rocks for oil, gas and gas‐condensates. For this study, nine metres of core from depths of more than 3400m from well X‐1 in the north‐central part of the basin were analysed for major variations in porosity and permeability in two Lower Goru sandstone units referred to as the Basal and Massive Sands. The Lower Goru Basal Sand was deposited in lower shoreface to inner shelf settings at the well location, while the Massive Sand was deposited in a middle to lower shoreface setting. In both units, intervals with moderate to good (> 15%) porosities alternate with intervals with very low porosity (<5%), and similar variations in core permeability were observed. In this paper, the reasons for this reservoir quality variation at well X‐1 are investigated. Specifically, the study addresses the influence of different clay types on reservoir porosity and permeability within the Lower Goru sands and the distribution and impact of hard cements such as calcite and quartz. A range of petrographical data is integrated including thin sections, whole rock and clay XRD results and SEM images, which together provide some insights into the causes of reservoir quality variation and into the paragenetic relationships between the authigenic minerals. Chlorite grain coats are present in the higher‐porosity sandstones and are interpreted to have inhibited the formation of quartz overgrowths. Dissolution of feldspar and volcanic rock fragments in both the Basal and Massive Sands has contributed to an increase in overall porosity at well X‐1. Relatively low porosity intervals in the Massive Sand are associated with the absence of chlorite grain coats and the presence of abundant quartz overgrowths. By contrast, low porosity intervals in the Basal Sand have undergone early poikilotopic calcite cementation. The formation of authigenic illite resulted in a significant decrease in permeability in both the Basal and Massive Sands. Chlorite and kaolinite also reduced the permeability. The chlorite originated mainly from the dissolution of volcanic rock fragments or from precursor depositional berthierine clay. The transformation of K‐feldspar to illite is suggested to be the main reaction responsible for the formation of both authigenic illite and quartz overgrowths in the two reservoir units; the observed pressure solution will also have contributed to development of quartz overgrowths.
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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 | 0.001 | 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 | 0.001 |
| 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 it