The Permian Basin has become the United States’ largest producer of oil over the past decade. Alo... more The Permian Basin has become the United States’ largest producer of oil over the past decade. Along with the rise in production, there has been an increase in the rate of low magnitude earthquakes,...
Our understanding of fractures in carbonate reservoirs is hindered by low data density, which pre... more Our understanding of fractures in carbonate reservoirs is hindered by low data density, which prevents effective fracture attribute mapping. Despite the advent of image logs and new core-recovery techniques, fracture data are frequently incomplete and sometimes misleading. Sparse sampling of large fractures remains unavoidable. From the interwell region, information is confined to seismic identification of faults and layer curvature. Although there may be a link between layer curvature and fracture intensity in situations where fractures develop during or after layer flexure, if fracturing predates flexure there is no such relationship. Collection of meaningful, systematic data at the well bore and extrapolation into the interwell volume are significant challenges.
2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, 2021
As the growth of interferometric synthetic aperture radar (In-SAR) data continues to accelerate, ... more As the growth of interferometric synthetic aperture radar (In-SAR) data continues to accelerate, there is an increasing need to detect surface deformation features from gigantic datasets in an automated fashion. We have developed a computer vision algorithm for automatic detection of InSAR deformation signals using multi-scale Laplacian-of-Gaussian (LoG) filters. We applied the algorithm to InSAR-derived land surface deformation maps in West Texas, where there has been a rise in the level of seismic activity near areas of hydrocarbon production. Our algorithm detected numerous surface deformation features without the need for manual inspection of signals. To control the false detection rate, here we employed a realistic tropospheric turbulence noise model and computed an empirical probability density for the magnitudes of candidate detections under the null hypothesis. We showed that the likelihoods from this PDF can be used to set an acceptable false detection rate for near real-time deformation monitoring applications.
SPE Annual Technical Conference and Exhibition, 2015
Multi-stage hydraulic fracturing together with horizontal drilling plays an important role in the... more Multi-stage hydraulic fracturing together with horizontal drilling plays an important role in the economic development of unconventional reservoirs. However, according to field analysis of stimulation effectiveness, only a small percentage of perforation clusters contribute to most of the well production. One reason for this low effectiveness is that multiple fractures do not take the same amount of fluid and proppant due to fracture interaction (i.e., stress shadow effects). Unfortunately, how best to minimize the negative effects of stress shadowing is still poorly understood in the petroleum industry. In this paper, we analyzed this problem in order to promote more uniform fracture growth using our complex hydraulic fracture development model. We employed our fracture propagation model that couples rock deformation and fluid flow in the fracture and horizontal wellbore. Partitioning of flow rate between multiple fractures was calculated by analogizing to the electric circuit netw...
Recent examples of hydraulic fracture diagnostic data suggest complex, multi-stranded hydraulic f... more Recent examples of hydraulic fracture diagnostic data suggest complex, multi-stranded hydraulic fractures geometry is a common occurrence. This reality is in stark contrast to the industry-standard design models based on the assumption of symmetric, planar, bi-wing geometry. The interaction between pre-existing natural fractures and the advancing hydraulic fracture is a key condition leading to complex fracture patterns. Performing hydraulic fracture design calculations under these less than ideal conditions requires modeling fracture intersections and tracking fluid fronts in the network of reactivated fissures. Whether a hydraulic fracture crosses or is arrested by a pre-existing natural fracture is controlled by shear strength and potential slippage at the fracture intersections, as well as potential debonding of sealed cracks in the near-tip region of a propagating hydraulic fracture. We present a complex hydraulic fracture pattern propagation model based on the Extended Finite ...
We are using DEM simulations in conjunction with experimental measurements of artificially cement... more We are using DEM simulations in conjunction with experimental measurements of artificially cemented laboratory specimens to investigate the effects of small amounts of inter‐granular cement on mechanical behavior. With current PC computing capabilities, it is possible to ...
Summary Wellbore stability in shale has been a crucial issue for drilling in all kinds of environ... more Summary Wellbore stability in shale has been a crucial issue for drilling in all kinds of environments. The analysis of time-dependent wellbore stability in shales has largely concentrated on the influence of fluid chemistry and filtrate invasion into the formation to predict compressive failure using poroelasticity and continuum models. This paper presents another possible mechanism for time-dependent behavior—stress-corrosion cracking (subcritical crack growth). Using the discrete-element method (DEM) to simulate grainscale processes, we apply the concept of time-dependent cracking to hole enlargement for vertical wellbores. We use a published example from the North Sea to verify the stress-corrosion model and demonstrate the application to wellbore stability in shale. Laboratory results on rocks indicate a wide range of susceptibility to stress-corrosion cracking related to rock petrology and contact-fluid chemistry. Using laboratory calibrated rock properties, we run 2D, plane-s...
SPE Annual Technical Conference and Exhibition, 2012
Field results in Steam Assisted Gravity Drainage (SAGD) heavy oil operations suggest formation pe... more Field results in Steam Assisted Gravity Drainage (SAGD) heavy oil operations suggest formation permeability changes during production operations. We investigate this process using samples constructed from loose Athabasca sand. Our results indicate that permeability changes (absolute and relative) and endpoint oil and water saturation variation are a function of loading boundary conditions. Triaxial loading paths (increasing mean stress) show increased permeability with sample dilatancy upon failure at low confining stress (100 to 400 psi) that diminishes when run at higher confining stress (800 psi). Residual oil saturation increases during compaction and decreases during dilation while initial water saturation decreases during compaction and increases during dilation. Radial extension tests (decreasing mean stress) result in larger increases in permeability upon failure and dilatancy, and lower residual oil and higher initial water saturations. Finally, failure induced by unloading...
Hydraulic fracture diagnostics have highlighted the potentially complex natural of hydraulic frac... more Hydraulic fracture diagnostics have highlighted the potentially complex natural of hydraulic fracture geometry and propagation. This has been particularly true in the cases of hydraulic fracture growth in naturally fractured reservoirs, where the induced fractures interact with pre-existing natural fractures. A simplified numerical model has been developed to account for mechanical interaction between pressurized fractures, and to examine the simultaneous propagation of multiple (>2) hydraulic fracture segments. Fracture intersection is presumed to communicate the hydraulic fracturing fluid to the natural fracture, which then takes up the continued propagation. Simulations for multi-stage horizontal well treatments and single stage vertical well treatments show that fracture pattern complexity is strongly controlled by the magnitude of the hydraulic fracture net pressure relative to the in situ horizontal differential stress as well as the geometry of the natural fractures. Analy...
Field experience in shale gas and some tight gas sandstones suggests significant interaction betw... more Field experience in shale gas and some tight gas sandstones suggests significant interaction between hydraulic fractures and natural fractures. Experimental analysis of this problem has mostly focused on frictional interfaces with regard to the natural fractures. We have performed tests to examine the effect of cemented natural fractures on hydraulic fracture propagation. The motivation for this type of work is that core observations from the Barnett and some other shale gas plays suggest that natural fractures are largely cemented (or healed) and trend obliquely or orthogonally to the present day hydraulic fracture direction. We embedded planar glass discontinuities into a cast hydrostone block as proxies for cemented natural fractures. Consistent with theoretical predictions, our results show that oblique embedded fractures are more likely to divert a fluid-driven hydraulic fracture than those occurring orthogonal to the induced fracture path. Hydraulic fracture – natural fracture...
Canadian Unconventional Resources Conference, 2011
Steam Assisted Gravity Drainage (SAGD) can cause dilatant shear failure in unconsolidated heavy o... more Steam Assisted Gravity Drainage (SAGD) can cause dilatant shear failure in unconsolidated heavy oil reservoirs. Our experimental work documents changes induced by such shear failure in absolute permeability, relative permeability to oil and water, and residual saturations. Tests were performed on 2 inch diameter synthetic specimens made from lower fine to medium grain size Ottawa sand formed with wet vibration to an initial porosity of about 32%. Loading paths included triaxial compression and radial extension. Axial and volumetric strains were measured directly during deformation, and single and two phase permeability tests were executed at axial strains of 1 to 10%. Triaxial compression tests followed a path of increasing mean stress (under constant confining stress) while radial extension tests provided a decreasing mean stress loading path (reducing confining stress under constant axial stress). The relative permeability was determined by the unsteady state method for relative p...
Wellbore stability in shale is a crucial issue for drilling in all kinds of environments. The ana... more Wellbore stability in shale is a crucial issue for drilling in all kinds of environments. The analysis of time-dependent wellbore stability in shales has largely concentrated on the influence of fluid chemistry and filtrate invasion into the formation to predict compressive failure using continuum models. Another possible mechanism for time-dependent behavior is stress corrosion cracking (subcritical crack growth), an important mechanism for the growth of natural tensile and shear fractures. Using discrete element method (DEM) to simulate grain-scale processes, we apply the concept of time-dependent cracking to hole enlargement for vertical wellbores. We use a published example from the North Sea to demonstrate the application of this new modeling approach to hole stability in shale. Laboratory results on rocks indicate a wide range of susceptibility to stress corrosion cracking related to rock petrology and contact fluid chemistry. Using laboratory calibrated rock properties, we ru...
Summary Using a fully coupled (flow and mechanics) hydraulic-fracture propagation model, we inves... more Summary Using a fully coupled (flow and mechanics) hydraulic-fracture propagation model, we investigate the critical in-situ and treatment factors controlling geometry in multiple-fracture horizontal wells. Fracture net pressure is calculated by considering continuity of flow rate and pressure equilibrium in the fracture and the wellbore between injection points. A 2D displacement-discontinuity method, with correction for finite fracture height, was used to calculate fracture aperture, accounting for mechanical interaction between multiple propagating fractures. Stress-shadow effects change the local stress field in the surrounding rock, influencing fracture geometry. A sensitivity study for simultaneous propagation was performed, including fracture spacing, velocity exponent, in-situ differential stress, fluid viscosity, and pump rate. The results show that closely spaced hydraulic fractures can cause significant fracture-width restriction, increasing the likelihood of premature sc...
The Permian Basin has become the United States’ largest producer of oil over the past decade. Alo... more The Permian Basin has become the United States’ largest producer of oil over the past decade. Along with the rise in production, there has been an increase in the rate of low magnitude earthquakes,...
Our understanding of fractures in carbonate reservoirs is hindered by low data density, which pre... more Our understanding of fractures in carbonate reservoirs is hindered by low data density, which prevents effective fracture attribute mapping. Despite the advent of image logs and new core-recovery techniques, fracture data are frequently incomplete and sometimes misleading. Sparse sampling of large fractures remains unavoidable. From the interwell region, information is confined to seismic identification of faults and layer curvature. Although there may be a link between layer curvature and fracture intensity in situations where fractures develop during or after layer flexure, if fracturing predates flexure there is no such relationship. Collection of meaningful, systematic data at the well bore and extrapolation into the interwell volume are significant challenges.
2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, 2021
As the growth of interferometric synthetic aperture radar (In-SAR) data continues to accelerate, ... more As the growth of interferometric synthetic aperture radar (In-SAR) data continues to accelerate, there is an increasing need to detect surface deformation features from gigantic datasets in an automated fashion. We have developed a computer vision algorithm for automatic detection of InSAR deformation signals using multi-scale Laplacian-of-Gaussian (LoG) filters. We applied the algorithm to InSAR-derived land surface deformation maps in West Texas, where there has been a rise in the level of seismic activity near areas of hydrocarbon production. Our algorithm detected numerous surface deformation features without the need for manual inspection of signals. To control the false detection rate, here we employed a realistic tropospheric turbulence noise model and computed an empirical probability density for the magnitudes of candidate detections under the null hypothesis. We showed that the likelihoods from this PDF can be used to set an acceptable false detection rate for near real-time deformation monitoring applications.
SPE Annual Technical Conference and Exhibition, 2015
Multi-stage hydraulic fracturing together with horizontal drilling plays an important role in the... more Multi-stage hydraulic fracturing together with horizontal drilling plays an important role in the economic development of unconventional reservoirs. However, according to field analysis of stimulation effectiveness, only a small percentage of perforation clusters contribute to most of the well production. One reason for this low effectiveness is that multiple fractures do not take the same amount of fluid and proppant due to fracture interaction (i.e., stress shadow effects). Unfortunately, how best to minimize the negative effects of stress shadowing is still poorly understood in the petroleum industry. In this paper, we analyzed this problem in order to promote more uniform fracture growth using our complex hydraulic fracture development model. We employed our fracture propagation model that couples rock deformation and fluid flow in the fracture and horizontal wellbore. Partitioning of flow rate between multiple fractures was calculated by analogizing to the electric circuit netw...
Recent examples of hydraulic fracture diagnostic data suggest complex, multi-stranded hydraulic f... more Recent examples of hydraulic fracture diagnostic data suggest complex, multi-stranded hydraulic fractures geometry is a common occurrence. This reality is in stark contrast to the industry-standard design models based on the assumption of symmetric, planar, bi-wing geometry. The interaction between pre-existing natural fractures and the advancing hydraulic fracture is a key condition leading to complex fracture patterns. Performing hydraulic fracture design calculations under these less than ideal conditions requires modeling fracture intersections and tracking fluid fronts in the network of reactivated fissures. Whether a hydraulic fracture crosses or is arrested by a pre-existing natural fracture is controlled by shear strength and potential slippage at the fracture intersections, as well as potential debonding of sealed cracks in the near-tip region of a propagating hydraulic fracture. We present a complex hydraulic fracture pattern propagation model based on the Extended Finite ...
We are using DEM simulations in conjunction with experimental measurements of artificially cement... more We are using DEM simulations in conjunction with experimental measurements of artificially cemented laboratory specimens to investigate the effects of small amounts of inter‐granular cement on mechanical behavior. With current PC computing capabilities, it is possible to ...
Summary Wellbore stability in shale has been a crucial issue for drilling in all kinds of environ... more Summary Wellbore stability in shale has been a crucial issue for drilling in all kinds of environments. The analysis of time-dependent wellbore stability in shales has largely concentrated on the influence of fluid chemistry and filtrate invasion into the formation to predict compressive failure using poroelasticity and continuum models. This paper presents another possible mechanism for time-dependent behavior—stress-corrosion cracking (subcritical crack growth). Using the discrete-element method (DEM) to simulate grainscale processes, we apply the concept of time-dependent cracking to hole enlargement for vertical wellbores. We use a published example from the North Sea to verify the stress-corrosion model and demonstrate the application to wellbore stability in shale. Laboratory results on rocks indicate a wide range of susceptibility to stress-corrosion cracking related to rock petrology and contact-fluid chemistry. Using laboratory calibrated rock properties, we run 2D, plane-s...
SPE Annual Technical Conference and Exhibition, 2012
Field results in Steam Assisted Gravity Drainage (SAGD) heavy oil operations suggest formation pe... more Field results in Steam Assisted Gravity Drainage (SAGD) heavy oil operations suggest formation permeability changes during production operations. We investigate this process using samples constructed from loose Athabasca sand. Our results indicate that permeability changes (absolute and relative) and endpoint oil and water saturation variation are a function of loading boundary conditions. Triaxial loading paths (increasing mean stress) show increased permeability with sample dilatancy upon failure at low confining stress (100 to 400 psi) that diminishes when run at higher confining stress (800 psi). Residual oil saturation increases during compaction and decreases during dilation while initial water saturation decreases during compaction and increases during dilation. Radial extension tests (decreasing mean stress) result in larger increases in permeability upon failure and dilatancy, and lower residual oil and higher initial water saturations. Finally, failure induced by unloading...
Hydraulic fracture diagnostics have highlighted the potentially complex natural of hydraulic frac... more Hydraulic fracture diagnostics have highlighted the potentially complex natural of hydraulic fracture geometry and propagation. This has been particularly true in the cases of hydraulic fracture growth in naturally fractured reservoirs, where the induced fractures interact with pre-existing natural fractures. A simplified numerical model has been developed to account for mechanical interaction between pressurized fractures, and to examine the simultaneous propagation of multiple (>2) hydraulic fracture segments. Fracture intersection is presumed to communicate the hydraulic fracturing fluid to the natural fracture, which then takes up the continued propagation. Simulations for multi-stage horizontal well treatments and single stage vertical well treatments show that fracture pattern complexity is strongly controlled by the magnitude of the hydraulic fracture net pressure relative to the in situ horizontal differential stress as well as the geometry of the natural fractures. Analy...
Field experience in shale gas and some tight gas sandstones suggests significant interaction betw... more Field experience in shale gas and some tight gas sandstones suggests significant interaction between hydraulic fractures and natural fractures. Experimental analysis of this problem has mostly focused on frictional interfaces with regard to the natural fractures. We have performed tests to examine the effect of cemented natural fractures on hydraulic fracture propagation. The motivation for this type of work is that core observations from the Barnett and some other shale gas plays suggest that natural fractures are largely cemented (or healed) and trend obliquely or orthogonally to the present day hydraulic fracture direction. We embedded planar glass discontinuities into a cast hydrostone block as proxies for cemented natural fractures. Consistent with theoretical predictions, our results show that oblique embedded fractures are more likely to divert a fluid-driven hydraulic fracture than those occurring orthogonal to the induced fracture path. Hydraulic fracture – natural fracture...
Canadian Unconventional Resources Conference, 2011
Steam Assisted Gravity Drainage (SAGD) can cause dilatant shear failure in unconsolidated heavy o... more Steam Assisted Gravity Drainage (SAGD) can cause dilatant shear failure in unconsolidated heavy oil reservoirs. Our experimental work documents changes induced by such shear failure in absolute permeability, relative permeability to oil and water, and residual saturations. Tests were performed on 2 inch diameter synthetic specimens made from lower fine to medium grain size Ottawa sand formed with wet vibration to an initial porosity of about 32%. Loading paths included triaxial compression and radial extension. Axial and volumetric strains were measured directly during deformation, and single and two phase permeability tests were executed at axial strains of 1 to 10%. Triaxial compression tests followed a path of increasing mean stress (under constant confining stress) while radial extension tests provided a decreasing mean stress loading path (reducing confining stress under constant axial stress). The relative permeability was determined by the unsteady state method for relative p...
Wellbore stability in shale is a crucial issue for drilling in all kinds of environments. The ana... more Wellbore stability in shale is a crucial issue for drilling in all kinds of environments. The analysis of time-dependent wellbore stability in shales has largely concentrated on the influence of fluid chemistry and filtrate invasion into the formation to predict compressive failure using continuum models. Another possible mechanism for time-dependent behavior is stress corrosion cracking (subcritical crack growth), an important mechanism for the growth of natural tensile and shear fractures. Using discrete element method (DEM) to simulate grain-scale processes, we apply the concept of time-dependent cracking to hole enlargement for vertical wellbores. We use a published example from the North Sea to demonstrate the application of this new modeling approach to hole stability in shale. Laboratory results on rocks indicate a wide range of susceptibility to stress corrosion cracking related to rock petrology and contact fluid chemistry. Using laboratory calibrated rock properties, we ru...
Summary Using a fully coupled (flow and mechanics) hydraulic-fracture propagation model, we inves... more Summary Using a fully coupled (flow and mechanics) hydraulic-fracture propagation model, we investigate the critical in-situ and treatment factors controlling geometry in multiple-fracture horizontal wells. Fracture net pressure is calculated by considering continuity of flow rate and pressure equilibrium in the fracture and the wellbore between injection points. A 2D displacement-discontinuity method, with correction for finite fracture height, was used to calculate fracture aperture, accounting for mechanical interaction between multiple propagating fractures. Stress-shadow effects change the local stress field in the surrounding rock, influencing fracture geometry. A sensitivity study for simultaneous propagation was performed, including fracture spacing, velocity exponent, in-situ differential stress, fluid viscosity, and pump rate. The results show that closely spaced hydraulic fractures can cause significant fracture-width restriction, increasing the likelihood of premature sc...
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