Ostadhassan, Mehdi - Academia.edu (original) (raw)
Papers by Ostadhassan, Mehdi
The importance of an accurate geomechanical model for borehole stability assessment is increasing... more The importance of an accurate geomechanical model for borehole stability assessment is increasing in the petroleum industry due to the growth in the number of drilling operations in unconventional reservoirs. These reservoirs are thin layered, naturally fractured with high clay content; the presence of clay minerals in particular, make their behavior to be unpredictable and also make the rocks to become chemically active with the drilling fluid. Thus, wellbore stability analysis is crucial and challenging; In addition a good understanding of elastic and physiochemical properties of the formation would be necessary for better field development to avoid future financial losses. For this study elastic, petrophysical and physicochemical properties of the shaly Bakken Formation were tested and reported from a several number of core plugs in different wells drilled in the Williston basin, North Dakota. We measured and reported various poro-mechanical, petrophysical and physiochemical properties of the Bakken shale along with the chemical properties of the drilling mud. The direction and the magnitude of the horizontal principal stresses were measured in the field with the data acquired from advanced logging tools in several wells. All of these values are coupled and used as input parameters in a time-dependent chemo-thermo-poroelastic constitutive model to calculate in-situ stresses and pore-pressure variations around the borehole. Changes in radial and hoop stresses were also plotted in the vicinity of the well. Mohr-Columb failure criterion was applied to the model to evaluate the deformations and failure occurrences around the borehole. Finally probabilistic risk assessment was carried out to understand the sensitivity of the results to the uncertainties in the input data.
Proceedings of the 3rd Unconventional Resources Technology Conference, 2015
Salt rock is characterized by its very low porosity and permeability along with excellent mechani... more Salt rock is characterized by its very low porosity and permeability along with excellent mechanical deformability. These characteristics make it a good cap rock for many structural petroleum reservoirs, a good geological hydrocarbon storage, and a suitable host rock for poisonous and hazardous wastes. Over the past few decades, different laboratory experiments have revealed the complexity and variety of mechanical behaviors of salt rocks. Although the elasto-plastic mechanical properties of salt rock highly depend on its stress state and temperature, but they can also change with its composition. Therefore, different salt rocks around the world show wide ranges of mechanical behaviors and it necessitates more experimental data from different geological regions. In this study 26 rock salt samples, with two different levels of impurities, from the Central Iranian salt rock were collected and examined. A set of rock mechanics experiments, including uniaxial compression test, triaxial ...
SPE Annual Technical Conference and Exhibition, 2011
ABSTRACT
SPE Eastern Regional Meeting, 2014
The importance of the geomechanical modeling and wellbore instability analysis is increasing in t... more The importance of the geomechanical modeling and wellbore instability analysis is increasing in the petroleum industry with recent growth of drilling plans in unconventional reservoirs. Recently, a large majority of field developments are occurring in shale oil and shale gas reservoirs as a novel source of energy. Many of these reservoirs are thin and highly layered, anisotropic and naturally fractured; these make their geomechanical modeling and wellbore instability analysis remarkably crucial; subsequently a good understanding of elastic properties of the formation such as Young's modulus, Poison's ratio and in-situ stresses are necessary for accurate results. Bakken Formation is one of the major unconventional plays in North America which is identified by three distinct members: layerd upper and lower shale and fractured middle dolomite. The thin beddings have made them extremely anisotropic, which originates from the platey shaped clay particles, high kerogen content plus the existence of natural fractures. This has made the wellbore instability analysis and modeling of this formation highly challenging. For this study elastic properties along with the petrophysical values are collected and reported from several numbers of cores along with the wireline log data. Then, these values are used as input parameters in poroelasticity equations to calculate the magnitude of the principal stresses for instability analysis especially in the inclined section of the well. Finite Difference 3D numerical modeling was conducted under Mohr-Columb failure criterion with anisotropic assumptions to evaluate the deformations around the wellbore for instable regions. In addition, the effects of different inclination angles of the wellbore versus depth were studied. Results indicated a strong of a relation between the magnitude of the wellbore deformations with the the drilling inclination angle from vertical to horizontal. Stress contours are plotted around the wellbore resulting in zones of higher stresses concenrteation and deformation. Different failure regions are developed as well.
SPE Eastern Regional Meeting, 2014
This study will provide insight to evaluate the potential risks involved with the alteration of i... more This study will provide insight to evaluate the potential risks involved with the alteration of in situ effective stresses around the borehole and the risks associated with the reservoir pressure decline. We studied how years of production and reservoir depletion may cause future major geological hazards in the area of study. Wellbore instability and stress distribution analysis around a vertical borehole is also carried out in the Bakken Formation including elastic anisotropy of the layer. We calculated the magnitude of maximum principal horizontal stress as a major input parameter through a new method. This study shows the importance of geomechanical modeling in the petroleum industry with the recent growth of drilling plans in unconventional reservoirs as a novel source of energy where many of them are fine layered, anisotropic and naturally fractured. For this study, dynamic elastic properties were collected through the Bakken Formation using advanced sonic logs. The interpretation of these data is significant in estimating the rock strength, pore pressure, and in situ stresses. The measured dynamic elastic moduli were converted to static ones and were used as input into poroelasticity equations to calculate the magnitude of the horizontal principal stresses. The direction of the maximum principal horizontal stress was determined to be N70E by analyzing fast shear azimuth (FSA) using major fractures which have caused more than 20% shear anisotropy. Finally stress analysis and wellbore stability were performed and compared in the current state of the reservoir stress state and after 5 years of production. Stress polygons are created in the reservoir (horizontal section of the well) to predict future natural hazards. The results confirm the possible occurrence of normal faulting in the region and existence of borehole breakouts after years of production.
The importance of an accurate geomechanical model for borehole stability assessment is increasing... more The importance of an accurate geomechanical model for borehole stability assessment is increasing in the petroleum industry due to the growth in the number of drilling operations in unconventional reservoirs. These reservoirs are thin layered, naturally fractured with high clay content; the presence of clay minerals in particular, make their behavior to be unpredictable and also make the rocks to become chemically active with the drilling fluid. Thus, wellbore stability analysis is crucial and challenging; In addition a good understanding of elastic and physiochemical properties of the formation would be necessary for better field development to avoid future financial losses. For this study elastic, petrophysical and physicochemical properties of the shaly Bakken Formation were tested and reported from a several number of core plugs in different wells drilled in the Williston basin, North Dakota. We measured and reported various poro-mechanical, petrophysical and physiochemical properties of the Bakken shale along with the chemical properties of the drilling mud. The direction and the magnitude of the horizontal principal stresses were measured in the field with the data acquired from advanced logging tools in several wells. All of these values are coupled and used as input parameters in a time-dependent chemo-thermo-poroelastic constitutive model to calculate in-situ stresses and pore-pressure variations around the borehole. Changes in radial and hoop stresses were also plotted in the vicinity of the well. Mohr-Columb failure criterion was applied to the model to evaluate the deformations and failure occurrences around the borehole. Finally probabilistic risk assessment was carried out to understand the sensitivity of the results to the uncertainties in the input data.
Proceedings of the 3rd Unconventional Resources Technology Conference, 2015
Salt rock is characterized by its very low porosity and permeability along with excellent mechani... more Salt rock is characterized by its very low porosity and permeability along with excellent mechanical deformability. These characteristics make it a good cap rock for many structural petroleum reservoirs, a good geological hydrocarbon storage, and a suitable host rock for poisonous and hazardous wastes. Over the past few decades, different laboratory experiments have revealed the complexity and variety of mechanical behaviors of salt rocks. Although the elasto-plastic mechanical properties of salt rock highly depend on its stress state and temperature, but they can also change with its composition. Therefore, different salt rocks around the world show wide ranges of mechanical behaviors and it necessitates more experimental data from different geological regions. In this study 26 rock salt samples, with two different levels of impurities, from the Central Iranian salt rock were collected and examined. A set of rock mechanics experiments, including uniaxial compression test, triaxial ...
SPE Annual Technical Conference and Exhibition, 2011
ABSTRACT
SPE Eastern Regional Meeting, 2014
The importance of the geomechanical modeling and wellbore instability analysis is increasing in t... more The importance of the geomechanical modeling and wellbore instability analysis is increasing in the petroleum industry with recent growth of drilling plans in unconventional reservoirs. Recently, a large majority of field developments are occurring in shale oil and shale gas reservoirs as a novel source of energy. Many of these reservoirs are thin and highly layered, anisotropic and naturally fractured; these make their geomechanical modeling and wellbore instability analysis remarkably crucial; subsequently a good understanding of elastic properties of the formation such as Young's modulus, Poison's ratio and in-situ stresses are necessary for accurate results. Bakken Formation is one of the major unconventional plays in North America which is identified by three distinct members: layerd upper and lower shale and fractured middle dolomite. The thin beddings have made them extremely anisotropic, which originates from the platey shaped clay particles, high kerogen content plus the existence of natural fractures. This has made the wellbore instability analysis and modeling of this formation highly challenging. For this study elastic properties along with the petrophysical values are collected and reported from several numbers of cores along with the wireline log data. Then, these values are used as input parameters in poroelasticity equations to calculate the magnitude of the principal stresses for instability analysis especially in the inclined section of the well. Finite Difference 3D numerical modeling was conducted under Mohr-Columb failure criterion with anisotropic assumptions to evaluate the deformations around the wellbore for instable regions. In addition, the effects of different inclination angles of the wellbore versus depth were studied. Results indicated a strong of a relation between the magnitude of the wellbore deformations with the the drilling inclination angle from vertical to horizontal. Stress contours are plotted around the wellbore resulting in zones of higher stresses concenrteation and deformation. Different failure regions are developed as well.
SPE Eastern Regional Meeting, 2014
This study will provide insight to evaluate the potential risks involved with the alteration of i... more This study will provide insight to evaluate the potential risks involved with the alteration of in situ effective stresses around the borehole and the risks associated with the reservoir pressure decline. We studied how years of production and reservoir depletion may cause future major geological hazards in the area of study. Wellbore instability and stress distribution analysis around a vertical borehole is also carried out in the Bakken Formation including elastic anisotropy of the layer. We calculated the magnitude of maximum principal horizontal stress as a major input parameter through a new method. This study shows the importance of geomechanical modeling in the petroleum industry with the recent growth of drilling plans in unconventional reservoirs as a novel source of energy where many of them are fine layered, anisotropic and naturally fractured. For this study, dynamic elastic properties were collected through the Bakken Formation using advanced sonic logs. The interpretation of these data is significant in estimating the rock strength, pore pressure, and in situ stresses. The measured dynamic elastic moduli were converted to static ones and were used as input into poroelasticity equations to calculate the magnitude of the horizontal principal stresses. The direction of the maximum principal horizontal stress was determined to be N70E by analyzing fast shear azimuth (FSA) using major fractures which have caused more than 20% shear anisotropy. Finally stress analysis and wellbore stability were performed and compared in the current state of the reservoir stress state and after 5 years of production. Stress polygons are created in the reservoir (horizontal section of the well) to predict future natural hazards. The results confirm the possible occurrence of normal faulting in the region and existence of borehole breakouts after years of production.