Pore pressure and stress distribution in a section perpendicular to the wellbore axis.
Reservoir Geomechanics and Seismicity Research Group
Overview:
The Reservoir Geomechanics and Seismicity Research (RGSR) at OU is recognized as a world-class experimental and numerical modeling research center. Current research focuses on experimental investigation of reservoir stimulation, propped and unpropped natural fracture response to thermo-poromechanical processes, in-situ stress determination and its variation by coupled processes and rock heterogeneity. The RGSR has been the largest reservoir geomechanics research group in North America for over a decade. The director of RGSR is Prof. Ahmad Ghassemi, a widely recognized geomechanics specialist with extensive teaching and research experiences of more than 27 years. The RGSR develops and applies new knowledge of geomechanics/rock mechanics through experimental and modeling activities to develop solutions for a variety of engineering problems related to conventional and unconventional reservoirs and geothermal systems (enhanced geothermal systems) such as hydraulic fracturing, induced seismicity, wellbore stability, DFIT, injection geomechanics, etc. The group has successfully completed several industry and DOE-sponsored projects (over 15 million dollars in value); most recently one dealing with stimulation characterization for enhanced geothermal systems which was recognized by GTO as a Success Story. The students within the RGSR have a unique opportunity to carry out cutting-edge research and to pursue their professional development. The RGSR group has a world-class rock mechanics facility consisting of 4 MTS Material Testing Systems, 3 Polyaxial Testing units, a Creep Test System, Fracture Conductivity Test System, 3D laser Scanning System and some Rock Preparation Tools (Diamond Cutting and Coring systems), etc. In addition to conventional rock mechanics testing, the center performs advanced/novel rock mechanics tests such as large-scale hydraulic fracturing test under true triaxial condition, tracer test, high-temperature and high-pressure tests, triaxial shear test, and fracture propagation and coalescence tests.
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Researchers at the University of Oklahoma conducted a rock fracturing experiment that showcased the potential for enhanced geothermal systems. |
Research Projects:
Enhanced Geothermal Systems (Reservoir stimulation, Zonal isolation, Induced seismicity)
Superhot Rock Geothermal (Rock mechanics, Drilling & wellbore integrity, Stimulation)
Proppant Development & Testing
Thermal Storage Research (Optimization of injection/production and Reservoir integrity)
Experimental Research and Testing:
The RGSR group has a world-class rock mechanics facility consisting of a number of MTS Material Testing Systems, 3 Polyaxial Testing units, 1 TTK Triaxial Test System, 1 Creep Test System, 1 API Fracturing Conductivity Test System, 3D laser Scanning System and some Rock Preparation Tools (Diamond Cutting and Coring systems), etc. In addition to conventional rock mechanics testing such as uniaxial/triaxial compressive, static/dynamic, tensile strength, AE monitoring, hardness, fracture conductivity, etc., we perform advanced/novel rock mechanics tests such as large-scale hydraulic fracturing test under true triaxial condition, tracer test, high temperature and high pressure test, triaxial shear test, direct shear test, fracture propagation and coalescence test.
Geothermal Reservoir Engineering Research
Our efforts aim to help technology development for energy production from high-grade geothermal resources including regular and super-hot EGS reservoirs. Rock deformation and fracture characteristics under high temperature and pressure are of fundamental significance to drilling and stimulation for geothermal resources. In particular, a major challenge in enhanced geothermal system (EGS) reservoir creation is creating controlled stimulated reservoir volume with sufficient contact area and flow capacity while minimizing uncontrolled seismicity. We develop solutions for efficient drilling and reservoir stimulation, as well as for production and reservoir management. Our research spans both fundamental and applied activities including experimental, numerical, and field demonstration. In addition, we collaborate with industry partners to develop techniques for using geothermal resources in conjunction with other renewables such as solar and wind.
Wellbore Integrity
The goal of this effort is to reduce non-drilling time by enabling safe and economical well design and construction for geothermal conditions.
A chart showing the transient, safe operating mud conditions associated with natural fractures intersecting a wellbore. Right: Analytical determination of safe mud weight requirements for drilling. This is a demonstration of mud weight calculations as a consequence of pore pressure, temperature, mechanical (stress) and chemical potential drivers, for different well bore orientations.
Top Row: Finite element analysis showing the distribution of pore pressure, temperature, brine concentration and rock damage for a wellbore drilled in a low permeability sedimentary rock (σHmax = 30 MPa,σhmin = 20 MPa). Higher damage is seen for the case σHmax = 18 MPa, σhmin = 12 MP (the red zone in the leftmost picture).
Bottom Two Rows: results of 3D simulation of a section of a wellbore subjected to overpressure and cooling. At the bottom right is a sketch of vertical failure planes. σv = 50 MPa, σH = 30 MPa, σh =30 MPa, pini = 19 MPa, pmud = 10 MPa. Colored zones indicate fmc > 0 (i.e., failure potential).
Propagation of drilling induced cracks obtained numerically (Tarasov and Ghassemi, 2012).
Influence of time and ratio of the total minimum to maximum horizontal stresses on crack propagation when there is thermal shock (Dobroskok and Ghassemi, 2005). The ordinate axis is time.
Bottomhole pressure needed for natural fracture slip as a function of dip and friction angle of a natural fracture potentially intersecting a wellbore (Nygren and Ghassemi, 2005).
Reservoir Creation & Management
The project aims to design and implement advanced reservoir stimulation concepts in different EGS setting including regular and super-hot rock reservoirs. Of particular emphasis improving near-wellbore and well-to-well conductivity while enhancing the stimulated reservoir volume (SRV) and promoting self-propping, and heat exchange.
Our work pertaining to modeling of stimulation in general and design and simulation of FHF includes extensive modeling of lab-scale (block tests), intermediate-scale (Collab) and field-scale (FORGE and Newberry EGS) stimulation. Over the last decade we have developed advanced modeling tools that can treat various stimulation concepts including fracture network modeling and seismicity, and single and multi-stage hydraulic fracturing.
EGS type stimulation in a large polyaxial frame with acoustic emission monitoring and fluid circulation to characterize permeability evolution.
Demonstration of mixed-mode fracturing at pressure below the minimum in-situ stress, a common occurrence in geothermal systems (Ye and Ghassemi, 2017).
Two stages of closely spaced hydraulic fractures for a specific wellbore layout. The spacing of sequential fractures in each zone is expected to be 4-8 ft but will be designed for optimum heat extraction. The fractures are expected to generate shear stress and slip on each other promoting dilation/self-propping. Wing fracture propagation from NFs are expected but not shown.
Two idealized fractures in Utah FORGE conditions; the fractures tend to grow more upward.
Formation of closely space fractures from one stimulation zone is possible (Sesetty and Ghassemi, 2019).
Reservoir Seismicity
Simulation of Utah FORGE April, 2022 stimulation (Stage 1) using an advanced 3D HF/NF model (Kumar and Ghassemi, 2022).
Simulation of Utah FORGE April, 2022 stimulation (Stage 3) using an advanced 3D HF/NF model (Kumar and Ghassemi, 2022).
Demonstration of shear slip, permeability increase and reservoirs seismicity (Ye and Ghassemi, 2018).
Zipper fracturing of deviated wells not aligned with minimum horizontal stress direction (i.e., x-axis), and deviated from the x-axis by 20º. Spacing between stages = 35 m, well spacing = 80 m. Simulation time = 42.9 min, propagation time = 225 s.
