Hydraulic fracturing under high temperature and pressure conditions with micro CT applications: Geothermal energy from hot dry rocks

Abstract Hydraulic fracturing has been widely employed to enhance the permeability of tight geological formations including deep geothermal reservoirs. However, due to the complex in-situ stresses, high-temperature conditions and heterogeneity of the formations, hydraulic fracturing under deep geothermal conditions is poorly understood to date. The aim of the current study is, therefore, to investigate the effect of reservoir depth, temperature, and sample heterogeneity during hydraulic fracturing and the influences of rock micro-structure on fracture propagation. A series of hydraulic fracturing experiments was conducted on two Australian granite types under a wide range of confining pressures from 0 to 60 MPa and temperatures from room temperature to 300 °C simulating different geothermal environments. The corresponding micro-structural effects on the rock matrix were investigated employing high-resolution CT imaging using the IMBL facility of the Australian Synchrotron. According to the results, the breakdown pressure of reservoir rock linearly increases with reservoir depth (confining pressure). However, with increasing temperature breakdown pressure linearly decreases. This corresponds to the linear reduction of tensile strength measured by high-temperature Brazilian tensile tests. In addition, CT images showed that the injection of cold water into hot rock can result in a porous zone with porosity ranging from 2 to 3% close to the wellbore due to thermally-induced inter- and intra-crystalline cracks. In this condition, fluid leak-off is high and the measured fracture aperture of the main hydraulic fracture is relatively small. Further, fracture propagation paths and apertures are mainly controlled by the stress state and the heterogeneity of the rock matrix. It was found that fractures tend to propagate along preferential paths, mainly along grain boundaries and in large quartz and biotite minerals (grain size > 0.3 mm) and minerals with pre-existing micro-cracks.

[1]  Jianjun Liu,et al.  A review on hydraulic fracturing of unconventional reservoir , 2015 .

[2]  Michael J. Mayerhofer,et al.  The Relationship Between Fracture Complexity, Reservoir Properties, and Fracture-Treatment Design , 2010 .

[3]  Shicheng Zhang,et al.  Experimental study of hydraulic fracturing for shale by stimulated reservoir volume , 2014 .

[4]  Yiyu Lu,et al.  Experimental study on crack propagation control and mechanism analysis of directional hydraulic fracturing , 2018 .

[5]  T. K. Perkins,et al.  Widths of Hydraulic Fractures , 1961 .

[6]  Yan Jin,et al.  Analysis of hydraulic fracture initiation and vertical propagation behavior in laminated shale formation , 2017 .

[7]  Ranjith Pathegama Gamage,et al.  Investigation of Depth and Injection Pressure Effects on Breakdown Pressure and Fracture Permeability of Shale Reservoirs: An Experimental Study , 2017 .

[8]  Giovanni Battista Barla,et al.  Comprehensive study including testing, monitoring and thermo-hydro modelling for design and implementation of a geothermal system in Torino (Italy) , 2017 .

[9]  F. Homand-Etienne,et al.  Thermally induced microcracking in granites: characterization and analysis , 1989 .

[10]  J. Geertsma,et al.  A Rapid Method of Predicting Width and Extent of Hydraulically Induced Fractures , 1969 .

[11]  Y. Fialko,et al.  Numerical simulation of high‐pressure rock tensile fracture experiments: Evidence of an increase in fracture energy with pressure? , 1997 .

[12]  Yaoru Liu,et al.  Investigation of directional hydraulic fracturing based on true tri-axial experiment and finite element modeling , 2016 .

[13]  A. Pabis,et al.  Density and temperature effect on hydrogen-bonded clusters in water - MD simulation study , 2008 .

[14]  Gioia Falcone,et al.  A systematic review of enhanced (or engineered) geothermal systems: past, present and future , 2013, Geothermal Energy.

[15]  V. Wall,et al.  Petrology of the Strathbogie Batholith; a cordierite-bearing granite , 1981 .

[16]  M. Haghighi,et al.  Experimental and numerical investigation into nano-stabilized foams in low permeability reservoir hydraulic fracturing applications , 2018 .

[17]  Takashi Akai,et al.  Evaluation of stimulated reservoir volume in laboratory hydraulic fracturing with oil, water and liquid carbon dioxide under microscopy using the fluorescence method , 2018 .

[18]  Yan Jin,et al.  Analysis of fracture propagation behavior and fracture geometry using a tri-axial fracturing system in naturally fractured reservoirs , 2008 .

[19]  M. G. Best.  Igneous and Metamorphic Petrology , 1982 .

[20]  Amin Nabipour,et al.  Steps for conducting a valid hydraulic fracturing laboratory test , 2013 .

[21]  Emmanuel M Detournay,et al.  Toughness-dominated Hydraulic Fracture with Leak-off , 2005 .

[22]  Guangqing Zhang,et al.  Laboratory investigation of hydraulic fracture networks in formations with continuous orthogonal fractures , 2014 .

[23]  P. Ranjith,et al.  Mechanical behaviour of Australian Strathbogie granite under in-situ stress and temperature conditions: An application to geothermal energy extraction , 2017 .

[24]  P. Ranjith,et al.  Temperature-dependent mechanical behaviour of Australian Strathbogie granite with different cooling treatments , 2017 .

[25]  B. Voight,et al.  Hydraulic fracturing theory for conditions of thermal stress , 1982 .

[26]  Teng-fong Wong,et al.  Thermal expansion of rocks; some measurements at high pressure , 1979 .

[27]  R. P. Nordgren,et al.  Propagation of a Vertical Hydraulic Fracture , 1972 .

[28]  Emmanuel M Detournay,et al.  Propagation Regimes of Fluid-Driven Fractures in Impermeable Rocks , 2004 .

[29]  Jonny Rutqvist,et al.  The role of hydromechanical coupling in fractured rock engineering , 2003 .

[30]  Mark D. Zoback,et al.  Laboratory hydraulic fracturing experiments in intact and pre-fractured rock , 1977 .

[31]  J. Fredrich,et al.  Micromechanics of thermally induced cracking in three crustal rocks , 1986 .

[32]  Allan H. Harvey,et al.  Physical properties of water , 2004 .

[33]  Xiao Li,et al.  Initiation, propagation, closure and morphology of hydraulic fractures in sandstone cores , 2017 .

[34]  Satish Karra,et al.  Shale gas and non-aqueous fracturing fluids: Opportunities and challenges for supercritical CO2 , 2015 .

[35]  Jose Adachi,et al.  Computer simulation of hydraulic fractures , 2007 .

[36]  Norman R. Warpinski,et al.  Influence of Geologic Discontinuities on Hydraulic Fracture Propagation (includes associated papers 17011 and 17074 ) , 1984 .

[37]  V. Rasouli,et al.  An Investigation of Hydraulic Fracturing Initiation and Near-Wellbore Propagation from Perforated Boreholes in Tight Formations , 2015, Rock Mechanics and Rock Engineering.

[38]  C. Sondergeld,et al.  An experimental investigation into hydraulic fracture propagation under different applied stresses in tight sands using acoustic emissions , 2013 .

[39]  Abbas Ali Daneshy,et al.  Hydraulic Fracture Propagation in Layered Formations , 1978 .