Experimental study of hydraulic fracturing for shale by stimulated reservoir volume

Abstract “Stimulated reservoir volume” (SRV) makes it possible for commercial production of shale gas by means of multistage fracturing of horizontal wells. However, the formation mechanism of effective fracture network has not been well understood. The mechanism of fracture propagation in shale with hydraulic fracturing needs to be further explored, in order to realize the control on morphology of fracture network with SRV and increase the single well production of shale gas. In this article, the true triaxial test system was deployed for horizontal well hydraulic fracturing simulation experiments of shale outcrops for the first time. The effects of multiple factors on propagating rules of fractures of horizontal well in shale with SRV were studied, and the fracture morphology of post-fracturing rock cores was observed for the first time by high-energy CT scanning using the large-scale non-destructive testing system based on linear accelerator. The results show that the influence of flow rate (for SRV) on fracture complexity differs when its value falls in different intervals. When the horizontal in situ stress difference is less than 9 MPa, the hydraulic fracture easily propagates along the natural fractures, forming a fracture network. In this range, when the stress difference is increased, the appearance of the main hydraulic fracture contributes to interconnecting more natural fractures, forming a relatively more complex fracture system. Under the condition of the same horizontal stress difference, if the coefficient of stress difference K h  > 0.25, there is an obvious trend to form single main fracture. The effects of viscosity of fracturing fluid and flow rate on the fracture propagation can be expressed by the parameter q ⋅ μ . When the order of magnitude of q ⋅ μ -value is 10 −9  N m, it is favorable to the generation of fracture network, but too small or too large values are both harmful. The development and cementing strength of depositional beddings seriously affect the propagating complexity of fracture network with hydraulic fracturing. Refracturing helps to produce some new fractures which are different from the initial ones, and better fracturing effect is achieved. The fracture initiation morphology in perforation fracturing is closely related to the distribution of natural fractures (depositional bedding) around the perforations. If the pressure curve fluctuates significantly, it is indicated that the shale core contains a large number of opened natural fractures or depositional beddings before fracturing, which causes the serious loss of fracturing fluid in the propagation process.

[1]  Mohamed Y. Soliman,et al.  Fracturing Design aimed at Enhancing Fracture Complexity , 2010 .

[2]  N. Goktan R.M. Gunes Yilmaz,et al.  A new methodology for the analysis of the relationship between rock brittleness index and drag pick cutting efficiency , 2005 .

[3]  X. Weng,et al.  Modeling of Hydraulic Fracture Network Propagation in a Naturally Fractured Formation , 2011 .

[4]  Huang Bing-xiang.  Research on theory and application of hydraulic fracture weakening for coal-rock mass , 2010 .

[5]  Christopher R. Clarkson,et al.  Pore structure characterization of North American shale gas reservoirs using USANS/SANS, gas adsorption, and mercury intrusion , 2013 .

[6]  C. Sondergeld,et al.  Mapping of Hydraulic Fractures under Triaxial Stress Conditions in Laboratory Experiments using Acoustic Emissions , 2012 .

[7]  R. Ewy,et al.  Shale Triaxial Strength Alteration due to Brine Exposure , 2008 .

[8]  Xiao Yong-shun.  Application of Large Industrial Computed Tomography in Nondestructive Testing of Key Components of Railway Vehicles , 2009 .

[9]  Laurent Molez,et al.  Shale dynamic properties and anisotropy under triaxial loading: experimental and theoretical investigations , 2007 .

[10]  Zhang Guangqing.  Experiment of propagation mechanism of hydraulic fracture in multi-fracture reservoir , 2008 .

[11]  Michael J. Mayerhofer,et al.  What is Stimulated Rock Volume , 2008 .

[12]  George E. King,et al.  Thirty Years of Gas Shale Fracturing: What Have We Learned? , 2010 .

[13]  R. Rickman,et al.  A Practical Use of Shale Petrophysics for Stimulation Design Optimization: All Shale Plays Are Not Clones of the Barnett Shale , 2008 .

[14]  J. Miskimins,et al.  Experimental Investigations of Hydraulic Fracture Growth Complexity in Slickwater Fracturing Treatments , 2010, TGC 2010.

[15]  R. Marc Bustin,et al.  Impact of mass balance calculations on adsorption capacities in microporous shale gas reservoirs , 2007 .

[16]  Yan Jin,et al.  Experimental investigation of hydraulic fracturing in random naturally fractured blocks , 2010 .

[17]  Larry Kevin Britt,et al.  The Geomechanics Of A Shale Play: What Makes A Shale Prospective , 2009 .

[18]  K. Sato,et al.  Experimental Hydraulic Fracture Propagation in a Multi-Fractured Medium , 2000 .

[19]  Alan D. Black,et al.  Laboratory Hydraulic Fracturing Test on a Rock With Artificial Discontinuities , 2006 .

[20]  Ted Urbancic,et al.  Microseismic Imaging of Hydraulic Fracture Complexity in the Barnett Shale , 2002 .

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

[22]  Brice Lecampion,et al.  Measuring Hydraulic Fracture Growth in Naturally Fractured Rock , 2009 .

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