Pengcheng Fu, Yue Hao, and Charles R. Carrigan Math, Science and Computation of Hydraulic Fracturing Workshop Stanford, March 21, 2013 This work was performed under the auspices of the U.S. Department of Energy by under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC
Included in these slides are interim results from a ongoing study. updated results. 2
Stimulate fracture system in hot rocks Circulate fluid through the fracture network to bring heat to surface 3
Fractures carrying more flow cools faster Thermal stress tends to loosen these fractures Flow might become more concentrated into a small number of fractures This is the primary mechanism for flow channeling A complex thermal-hydrologic-mechanical process Questions to answer: How it affects reservoir performance? 4
Rock joint model Aperture width Eff. on fracture DFN flow model Fracture flow network Solid FEM T field TH flow model 5
Rock joint model Aperture width Eff. on fracture DFN flow model Fracture flow network Solid FEM T field TH flow model 6
Rock joint model Aperture width Eff. on fracture DFN flow model Fracture flow network Solid FEM T field TH flow model 7
Rock joint model Aperture width Eff. on fracture DFN flow model Fracture flow network Solid FEM T field TH flow model 8
H =25 MPa Regular grid pattern with two orthogonal sets Fracture spacing 20m Natural pore pressure 15 MPa Closed-loop circulation at a constant flow rate. h =17 MPa T 0 =150 C Injection at 50 C 9
Initial flow rate distribution 10
T, 10 Years Produciton Temperature ( C) 160 150 140 130 120 110 100 90 80 0 60 120 180 240 300 360 Time of production (month) T, 20 Years 11
Initial With TM 10 year later 12
Infinite medium T x ae T L ( a b)(1 ) 2b 2a T y be T L ( a b)(1 ) y x Cooling zone, T 13
Initial 10 years 10 year production Stress_xx Stress_yy 14
Assumptions: Fracture network consists of at least two fracture sets Well layout perpendicular to the minimum principal stress direction Resulting in: Flow in primary fracture set is fed by the secondary set Secondary set is the bottleneck, preventing a more diffuse flow pattern Cooling zone elongates along the primary set Greater thermal stress on the secondary set 15
W/o TM 10- year production 160 Produciton Temperature ( C) 150 140 130 120 110 100 90 With TM effects W/o TM effects With TM 10 year production 80 0 60 120 180 240 300 360 Time of production (month) 16
Network I 17
Produciton Temperature ( C) 160 150 140 130 120 110 100 90 80 With TM effects W/o TM effects 0 60 120 180 240 300 360 Time of production (month) W/o TM 20- Y production With TM 20- Y production 18
Network I Network II 19
Produciton Temperature ( C) 160 150 140 130 120 110 100 90 80 With TM effects W/o TM effects 0 60 120 180 240 300 360 Time of production (month) W/o TM 20- Y production With TM 20- Y production 20
Network I Network III Network II 21
Produciton Temperature ( C) 160 150 140 130 120 110 100 90 80 With TM effects W/o TM effects 0 60 120 180 240 300 360 Time of production (month) W/o TM 20- Y production With TM 20- Y production 22
Network I Network IV Network II Network III 23
Produciton Temperature ( C) 160 150 140 130 120 110 100 90 80 With TM effects W/o TM effects 0 60 120 180 240 300 360 Time of production (month) W/o TM 10- Y production With TM 10- Y production 24
Thermal drawdown does affect flow pattern We discovered a natural mechanism that counteracts flow channeling Related to anisotropy in thermal stress The extent of flow channeling is remarkably affected by natural fracture network patterns TM effects have a moderate effects on the arrival of thermal breakthrough (two mechanisms counteracting each other) Usually not a disastrous; also reduces pumping effort. TM effects substantially reduces the post-breakthrough value of reservoirs 25
This work was performed under the auspices of the U.S. Department of Energy by under Contract DE- AC52-07NA27344. Predicting stimulation-response relationships for engineered geothermal reservoirs Creating Optimal Fracture Networks (#11-SI-006) Release number: 26