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Collaborating Authors
51st U.S. Rock Mechanics/Geomechanics Symposium
ABSTRACT: Fracture coalescence tests in rocks and rock-like materials have been extensively conducted in the laboratory over the past 40 years. Its mechanism has not been fully understood. Acoustic emission monitoring and moment tensor inversion technique cast a light in investigating the accumulation of micro-meso-scale fracture (damage) before the macro-fracture-propagation-stage of fracture coalescence. To this end, reliable sensor calibration is highly warranted to ensure the AE information is readily usable in moment tensor analysis. This paper presents and compares the calibration attempts by three types of sources, namely, breaking pencil lead source, ball drop source, and the source generated by the electrically energized piezoelectric sensor. By comparing these three source types for calibration, their advantages and disadvantages are identified. The ball drop source is the most suitable source among these three types of sources for the calibration in small scale prismatic rock blocks containing preexisting flaws for fracture coalescence tests. The polarity of the pencil lead source is its major disadvantage. The source generated by piezoelectric sensor has the highest repeatability among the three. However the aperture of the sensor and the strict requirement on the over-determined condition of the calibration equation system are the major problems in using it.
- Asia (0.28)
- North America > United States > California (0.28)
Understanding Stress Reorientation Process in Shale Gas Play and Its Impact on Refracturing Time Window
Xia, K. (Shell International Exploration and Production Inc.) | Mondal, S. (Shell International Exploration and Production Inc.) | Fonseca, E. (Shell International Exploration and Production Inc.) | Jones, R. (Shell International Exploration and Production Inc.)
ABSTRACT: The potential of refracturing horizontal wells to boost production in unconventional gas development is getting more attention. After a refracturing candidate is identified based on a certain criteria, it is important to evaluate whether the planned fractures at the selected locations can propagate in the desired direction. Hydraulic fractures generally propagate in the direction of maximum horizontal stress (relatively larger horizontal compression stress). Therefore the feasibility of refracturing can be evaluated based on the time-varying stress state or stress reorientation of the maximum and minimum horizontal stresses due to pre-existing fractures and subsequent production. To capture this stress change process, a numerical model with detailed formation layers based on poroelasticity is developed. The model includes some pre-existing sharp-tip fractures and the fracture geometries were estimated using a separate hydraulic fracture simulator. Also the fracture surfaces are defined as contact pairs and allowed to contact or separate depending on the deformation continuity in the formation. Several load steps are used in the model, which can subsequently calculate the in-situ stresses and overpressure in pay zone, stress state change due to pre-existing and new fracturesโ openings, and the most concerned ones during fracture production process. The numerical model can capture the whole picture of stress reorientation process due to hydraulic fracture treatment and reservoir production. Based on the stress change due to fracture opening and production rate, the right refracturing time window can be evaluated for planning new fractures at the desired locations. Numerical sensitivity study to key parameters was conducted to understand their impacts on refracturing time window. 1. INTRODUCTION
- North America > United States > Texas (0.46)
- North America > United States > California (0.46)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.43)
- Geology > Petroleum Play Type > Unconventional Play > Shale Play > Shale Gas Play (0.41)
ABSTRACT: The Mayo โAโ powerhouse was constructed in 1951 and has brought clean efficient power to the central Yukon since this time. The powerhouse at Mayo was constructed adjacent to a 70 m high heterogeneous rock and soil slope with minimal catchment between the slope and the powerhouse building. Following a series of near misses and actual impacts from rock fall onto the roof and sidewall of the building, Tetra Tech were commissioned to assess and remediate the rock fall hazard. To mitigate the hazard in such a spatially constrained site, with critical infrastructure both at the base and on the slope, required a departure from the traditional scaling and remediation approach. Instead, a staged construction and hazard mitigation schedule was adopted, requiring a number of innovative techniques and solutions. The resulting design included the installation of a passive mesh system around very unstable masses of poor quality rock, prior to the construction of a catch fence, and use of a construction chute for scaling of rock immediately above the powerhouse. This paper details some of the unique challenges and solutions adopted on this site, allowing for successful construction completion within three months of initial assessment.
ABSTRACT: The role of faults and natural fractures on hydraulic fracture stimulation in the Vaca Muerta Play, of the Neuquรฉn basin, Argentina, is investigated using a 3D, fully coupled, fracture and fluid flow simulator. During the development of the Vaca Muerta Shale, and due to the complex nature of the geology and geomechanical conditions of the play, well interference has been observed while pumping a vertical well. Microseismic events recorded during stimulation show a map-view โZโ pattern that has not been observed before and potentially identifies a trend of preexisting natural fractures/faults striking NE-SW and NW-SW, and steeply dipping that could hydraulically connect adjacent wells. We used a 3D coupled flow and geomechanical simulator to evaluate the geometric characteristics and material and fault properties that could produce well interference using the field parameters utilized during the stimulation operations in the study pad, and that would produce comparable synthetic microseismicity. Simulation results show that fluid pressure can communicate through sufficiently conductive faults for relatively long distances between 300 m and 700 m. In the case investigated here, hydraulic fractures can be arrested by faults and reinitiate from its tip. Fracture height growth exceeds the estimated propped height, consistent with the distribution of microseismicity. Results also indicate that the microseismic event cloud distribution follows large-scale structures, and therefore the presence of conductive faults could explain the well interference problems observed in the field.
- South America > Argentina > Patagonia Region (1.00)
- South America > Argentina > Neuquรฉn Province > Neuquรฉn (1.00)
- Research Report > New Finding (0.35)
- Research Report > Experimental Study (0.34)
- Geology > Structural Geology > Fault (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Petroleum Play Type > Unconventional Play > Shale Play (0.49)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.36)
- South America > Argentina > Patagonia > Neuquรฉn > Neuquen Basin > Vaca Muerta Shale Formation (0.99)
- South America > Argentina > Patagonia > Neuquรฉn > Neuquen Basin > Loma Campana Field > Vaca Muerta Shale Formation (0.99)
- South America > Argentina > Patagonia > Neuquรฉn > Neuquen Basin > Loma Campana Field > Lower Agrio Formation (0.99)
- (11 more...)
ABSTRACT: Though employing low grouting pressure in rock mass results in a decrease of length of grout penetration and ends up with an incomplete grouting process, conversely, high grouting pressure may cause undesired fracture initiation. Hence, prediction of minimum required rock mass grouting pressure to overcome these two consequences is crucial. The paper describes an application of Newtonโs second law along with the principles of fracture mechanics to predict the minimal rock mass grouting pressure for Khairabad earth dam rock foundation in Iran. The results of quality control of post grouting based on drilling of the grouted rock mass at the dam foundation revealed that, further grouting information is required to verify the applicability and credibility of the proposed method.
- Asia > Middle East > Iran (0.36)
- North America > United States > California (0.28)
ABSTRACT: This study reports on strength measurements performed on sandstone samples from a shallow offshore field and is part of a larger petrophysical evaluation including static and dynamic elastic properties under various stress conditions. The samples tested were retrieved from three one-foot-long preserved core sections spanning a depth range of about 20 meters. For each depth, three types of mechanical tests were performed: brazilian tensile test, unconfined compression test (UCS) and confined compression test with ultrasonic wave velocity monitoring along and perpendicular to the plug axis. The mechanical data are augmented with X-ray CT image volumes acquired pre-test and post-test in order to elucidate some of the observations as well as to outline possible elements of a laboratory workflow that would comprise image-based heterogeneity assessment and prediction. We emphasize in particular the fact that if such workflow is to be standardized, care should be taken in acquiring properly calibrated plug scale X-ray images in order to allow heterogeneity quantification and its use as an input into future predictive models.
- Research Report (0.34)
- Overview (0.34)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.62)
ABSTRACT: Slope stability and maximum productivity are critical to the success of any open pit mine. To achieve a profitable balance of the two, the slope has to be steep enough to minimize waste stripping and gentle enough to ensure slope stability. One means to this end is careful interpretation of slope monitoring data. This paper presents a real life case study of a platinum open pit mine which had been plagued with slope stability challenges and how slope monitoring data interpretation techniques were used to restore and enhance stability. Through monitoring data analysis the investigation identified that the hangingwall of the North Pit of the mine showed progressive movement with maximum movement found to be 8.5 mm/day. This proved a hypothesis that there is a crack existing behind the slopes. Routine inspections of the mine were done with the purpose to identify geological structures, hazardous conditions and review the quality of the highwall. The conditions of the footwalls were found to be fairly good and it is recommended that the same mining technique carried out when blasting trim benches in the footwall need to be carried out in hangingwall. The implementation of new technology in slope monitoring manages to solve slope failure challenges, however there is also need to optimise costs such that the most effective less costly technologies are implemented. In this light, this study highlights the practical applicability of different slope monitoring technologies including GroundProbe Slope Stability Radar, IBIS radar systems and GeoMos.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.46)
Monitoring the Growth of Hydraulic Fractures With Fiber Optic Strain Technology
Scott, T. E. (Shell International Exploration and Production Company) | Gage, C. (Shell International Exploration and Production Company) | Martinez, R. (Shell International Exploration and Production Company) | Dudley, J. W. (Shell International Exploration and Production Company)
ABSTRACT: Tracking the development of hydraulic fracture (HF) propagation in the laboratory and in the field has always been difficult, especially in cases where multiple HFs are propagating simultaneously. A new method is presented using fiber optic (FO) technology to monitor the hydraulic fracturing process during real time. The method has been proven using FO cables โwovenโ in a grid pattern and cast inside 46 cm (18 inch) cubic blocks of cement. Some of these blocks were then placed in a large cubic polyaxial load frame and subjected to a true triaxial state of stress during the fracturing operation. The FO cable acts essentially as a long continuous โstrain gageโ in the direction of the cable. As a HF propagates across each FO cable segment it sharply strains each one. This process allows a real time tracking of the position of the growing hydraulic fracture crack tip during testing. The technique is being used to track single HFs, multiple HFs, and leak- off haloes in polyaxial HF block testing.
- Information Technology > Communications > Networks (0.73)
- Information Technology > Architecture > Real Time Systems (0.57)
ABSTRACT: The laboratory experiments typically performed to measure poroelastic properties evaluate the macroscopic deformation of samples. While these techniques are adequate for capturing bulk effects, they fail to capture fine detail related to the actual deformation of constituent mineral phases because the measurement captures the combined effect of pore network geometry change and polymineralic deformation. A more precise measurement of mineral deformation in fluid saturated porous media has the potential to improve understanding of poroelastic behavior and material failure where pore pressure is present.
- North America > United States > Tennessee (0.28)
- North America > United States > California (0.28)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
ABSTRACT: Simulating pressure changes and production processes in natural fractured formations has been commonly performed by the classic dual-porosity model. Geomechanics can be crucial for pressure change and production as both formation deformation and locally induced stresses may contribute to skeleton deformation and the pressure change thus production significantly, particularly in low-permeability and fractured formations. Multiphase flow in both the matrix and fractured system can significantly affect the production and pressure results, particularly near a wellbore or a hydraulic fracture. The key parts on developing this model are to come up an efficient algorithm and to define the parameters characterizing the geomechanics coupling to the flow on top of the explicit coupling to the saturation, where upstream weighting normally is applied. The proposed algorithm coupled the pressures from both system with the corresponding volumetric strain and subsequently explicitly coupled to the saturation. Both a generalized Galerkin and Petrov-Galerkin finite methods are used in which mixed quadratic and linear shape functions are implemented respectively for the displacement and pressures, yet only quadratic weighting function is used in the calculation of saturation and for the entire weighting function. A unique weighting function with different P-G coefficient is also proposed and tested for saturation calculation. Results for saturation and pore pressure near a wellbore during a pressurization are generated and discussed, simulating fracturing process in naturally fractured reservoirs.