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ABSTRACT The last decade has seen a significantly increased interest in microseismic monitoring by the hydrocarbon industry due to the recent surge in unconventional resources such as shale-gas and heavy-oil plays. Both hydraulic fracturing and steam injection create changes in local pore pressures and in situ stresses and thereby brittle failure in intact rock plus additional slip/shearing in naturally fractured rock. Local rock failure or slip yields an acoustic emission, which is also known as a microseismic event. The microseismic cloud represents thus a volumetric map of the extent of induced fracture shearing, opening and closing. Microseismic monitoring can provide pertinent information on in situ reservoir deformation due to fluid stimulation, thus ultimately facilitating reservoir drainage. This paper reviews some of the current key questions and research in microseismicity, ranging from acquisition, processing to interpretation.
- North America > United States (1.00)
- Europe (1.00)
- North America > Canada > Alberta (0.46)
- Geology > Structural Geology > Fault (1.00)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- (2 more...)
- North America > United States > Louisiana > Cotton Valley Field (0.99)
- Europe > United Kingdom > England > Bowland Basin > Bowland Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > Block 2/8 > Valhall Field > Tor Formation (0.99)
- (3 more...)
Enhanced Interpretation of Fracturing From Acoustic Emissions And Ultrasonic Monitoring At the Aspö Pillar Stability Experiment
Haycox, J. R. (Applied Seismology Consultants Ltd) | Moretti, H. C. (Applied Seismology Consultants Ltd) | Reyes-Montes, J. M. (Applied Seismology Consultants Ltd) | Young, R. P. (University of Toronto)
Abstract: The Aspö Pillar Stability Experiment (APSE) was a full-scale demonstration project at SKB's Hard Rock Laboratory undertaken to examine the failure process in a heterogeneous and fractured crystalline rock mass when subjected to coupled excavation-induced and thermal-induced stresses. A pillar was produced by excavating two 1.8 m diameter deposition holes 1m apart. An ultrasonic acquisition system provided acoustic emission (AE) and ultrasonic survey monitoring throughout the various phases of the experiment to map microcracks and measure changes in rock properties. This paper builds on previous work by performing advanced processing and interpretation methods on the data. The data set of 15,198 AEs shows an intense clustering of events located along the length of the deposition holes. Event clusters are primarily constrained to a damage zone orthogonal to the maximum principal stress, represented by a semi-circle of tightly packed AEs extending from the edge of each hole approximately 20 cm into the pillar. B-value analysis helps to characterise the stress and tectonics of a region globally, but can be used at AE scales to provide an insight into stress build-up and release mechanisms. In the APSE experiment, a close relationship has been found between spalling volume and b-value. The fracture geometry from statistical analysis of AE locations shows the evolution of the dominant structure of the induced fracture network. The results from these approaches increase our understanding of the fracture mechanisms and allow additional information to be gained from the AE catalogue. 1 INTRODUCTION Microseismic, acoustic emission (AE) and ultrasonic techniques are scaled seismic studies that can be used to remotely monitor rock mass deformation and fracturing around engineered structures. Performing b-value analysis and investigating fracture geometry from statistical analysis of AE locations provide additional insights into why the rock responds the way it does.
- North America > Canada (0.47)
- Europe > United Kingdom > England > Staffordshire (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.50)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (0.89)
Identification of Activated Fracture Networks Using Microseismic Spatial Anomalies, b-values, and Magnitude Analyses in Horn River Basin
Yousefzadeh, Abdolnaser (Schulich School of Engineering, University of Calgary) | Li, Qi (Schulich School of Engineering, University of Calgary) | Virues, Claudio (CNOOC- Nexen) | Aguilera, Roberto (Schulich School of Engineering, University of Calgary)
Abstract We analyzed microseismic spatial and temporal distribution, magnitudes, b-values and treatment data to interpret and explain the observed anomalies in microseismic events recorded during exploitation of Shale Gas reservoirs in the Horn River Basin of Canada. We estimated the directional diffusivity to define the microseismicity front curve for each stage of hydraulic fracturing. Based on our definition of front curves, we managed to separate most of the microseismic events data that are related to natural fracture activation from hydraulic fracturing events. We analyzed the b-values for microseismic events of each stage before and after separating fracture activation microseismic events from original data and created a map of b-values in the study area. This allowed us to locate activated fractures mostly in the northeastern part of the study well pad. The b- value map agrees with our assumption of activated fracture locations and high ratio of seismic activities. Suggested fracture locations agree with anomalous events' density, energy distribution and treatment data. We are defining and proposing intermediate b-values for calculation of the stimulated reservoir volume (SRV) in areas with both hydraulically fractured events and events related to natural fracture network activation in those instances where the separation of events based on their origin is not viable.
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Geological Subdiscipline > Geomechanics (0.93)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.36)
- North America > United States > Kansas > Thomas Lease > Simpson Formation (0.99)
- North America > Canada > British Columbia > Western Canada Sedimentary Basin > Horn River Basin > Muskwa Field > Muskwa Formation (0.99)
- North America > Canada > Alberta > Western Canada Sedimentary Basin > Zama Virgo Basin > Keg River Formation (0.99)
- North America > Canada > British Columbia > Western Canada Sedimentary Basin > Horn River Basin > Otter Park Formation (0.94)
ABSTRACT Microseismic source mechanisms (obtained through moment-tensor inversion) provide an understanding of the hydraulic fracturing behavior of a stimulated reservoir, knowledge of which can help to improve production and minimize seismic risk. Seismic source inversion, Gutenberg-Richter -value analysis, and geomechanical considerations are carried out to investigate the fracturing behavior for a microseismic data set recorded in the West Pembina field of central Alberta, Canada. A spatial pattern in the fracturing behavior seems apparent in the source mechanism results, showing strong tensile components in between the two observation wells and parallel to the treatment well, and shear-dominated failure mechanisms outside of this zone. This gives the impression that the reservoir experiences two spatially different fracturing behaviors. However, reliability tests using an identical monitoring geometry demonstrate that the change in behavior coincides with a region of unreliable moment-tensor solutions. This region occurs between the two observation wells, casting doubt on the recovered tensile failure mechanisms, thus indicating that only shear-dominated failure is likely to occur. This demonstrates the importance of taking into account the reliability of moment-tensor solutions when interpreting the fracturing behavior of a reservoir. Conversely, analysis of -values indicates changes in the behavior between the reservoir (high -values) and the sandwiching formations (-values closer to one), which is likely due to a lower differential stress within the reservoir, caused by surrounding load-bearing formations. Geomechanical considerations also explain the observed polarity changes in shearing mechanisms as caused by either forward and then reversed slip on preexisting weaknesses or opposing shear motion on either side of the main hydraulic fractures.
- North America > Canada > Alberta > Yellowhead County (0.61)
- North America > Canada > Alberta > Wetaskiwin County No. 10 (0.61)
- North America > Canada > Alberta > Ponoka County (0.61)
- (3 more...)
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.48)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.31)
- North America > United States > West Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- North America > United States > Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- North America > United States > Pennsylvania > Appalachian Basin > Marcellus Shale Formation (0.99)
- (13 more...)
Abstract We carried out an integrated geomechanical and microseismic analysis of a gas shale production pad in the Horn River Basin containing 16 horizontal wells, over 270 individual hydraulic fracture stages, and more than 15,000 located microseismic events to better characterize the reservoir response to hydraulic fracture stimulations. Geomechanical constraints indicate that the pad is generally characterized by a strike-slip stress regime (SHmax > SV > Shmin) with the maximum horizontal stress (SHmax) oriented NE-SW. A pre-existing NNE-SSW-trending fault passes through the pad and appears to be well-oriented for slip in the current stress field. Measurements of Shmin, the minimum principal stress, are moderately elevated in some stages in the vicinity of this fault, and also appear to gradually increase from toe to heel in most wells. Microseismic b-values, which quantify magnitude scaling relationships for a population of events, vary from stage to stage but typically range between 1.0 and 2.5, indicating a relative abundance of small magnitude to large magnitude events compared to naturally-occurring earthquake populations (b ≈ 1.0). This observation has also been reported in other shale gas stimulation projects. We also utilize the double-difference relocation technique in an attempt to improve the accuracy of microseismic event hypocenters recorded during individual hydraulic fracture stages. The technique produces a clear hypocenter lineation, which unfortunately appears to be an artifact arising from the limited monitoring array configuration and not an actual structure within the reservoir. Finally, we analyze a population of microseismic events recorded during a single hydraulic fracture stage and find that the events can be broken into small sub-groups of events based on high waveform similarity, which suggests repeated slip on small-scale reservoir structures. We conclude that reservoir response to hydraulic fracturing is generally characterized by seismic deformation occurring on small fractures created or reactivated by the hydraulic fracturing stimulations, although there is also some evidence for seismic deformation occurring on larger-scale localized structures within the reservoir.
- North America > United States > Texas (1.00)
- North America > Canada > British Columbia (1.00)
- Europe (1.00)
- Asia (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- North America > United States > Texas > Sabine Uplift > Carthage Cotton Valley Field > Cotton Valley Group Formation > Cotton Valley Sand Formation (0.99)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- North America > Canada > Saskatchewan > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- (10 more...)