High Pressure Stimulation – Impact of Hydraulic Fracture Geometry to Unconventional Gas Appraisal and Development in Compressional Settings
Bibliographic record
Abstract
Abstract For unconventional resources exploration and development, hydraulic fracture pattern, geometry and associated dimensions are critical elements in determining if the uneconomically low-permeability reservoirs can be effectively and efficiently stimulated. In principle, hydraulic fracture growth pattern is dominated by the state of stress in the subsurface, and commonly and optimally, hydraulic fractures are expected to grow vertically from deep wells and to have sufficient height growth to connect stacked hydrocarbon-bearing and horizontally more permeable reservoir packages while being contained to stay away from water-rich intervals. While the tectonic setting and in-situ stress conditions for vertical fracture development have been well studied, those for horizontal or complex fractures remain unclear or not well reported. In this paper, a case study is presented on the complex hydraulic fracture in a highly over-pressured and tectonically stressed tight gas field in the Sichuan Basin of southwest China. During deep well hydraulic stimulation of the primary reservoirs of the Upper Triassic Xujiahe formation in the central western Sichuan Basin, difficulties are encountered in formation breakdown, injectivity establishment, proppant placement, pump equipment shut down, continuous high treating pressures, casing shear, and screen-out. These difficulties are preceded by larger-than-overburden breakdown pressures and ISIPs (Instantaneous Shut-In Pressure) during diagnostic pre-fracture injection tests, which imply that hydraulic fracture may have initiated and propagated horizontally. Different fracture monitoring techniques, however, have indicated that instead of getting purely horizontal fracture geometry, hydraulic fractures may have formed a complex network characteristic of T-shape or I-shape geometry. The main causes for such complex fracture geometry and limited fracture height are investigated and studied. To quantitatively evaluate the fracturing performance and strategy, two classes of numerical hydraulic fracture models are undertaken. In addition to the LEFM (Linear Elastic Fracture Mechanics) based hydraulic fracture simulation, a fully-coupled finite-element based model is developed that takes into account a full suite of rock mechanical properties of sandstone and shale sequences and geological features that may limit or facilitate the fracture growth. The modeling results indicate that in addition to the typical stress control on the growth of fracture height, contrast in mechanical property and the presence of bed-parallel geological features may act as fracture baffles or barriers that prematurely arrest the vertical growth and facilitate development of horizontal fractures.
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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 | 0.000 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 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 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".