Theoretical and Experimental Research on Hydraulic Fracturing

Abstract

We are conducting a joint theoretical/experimental research program on hydraulic fracturing. Newly developed two-dimensional numerical models (which include complete descriptions of the elastic continuum and porous flow fluids) have been applied to analyze the effects of pore pressure on the fracturing process. By means of small-scale experiments, we are acquiring a better understanding of the effects of the in-situ stress field, the porosity and permeability of the solid, and the presence of interfaces or layering in the solid. Experimentally, we have been studying the growth of cracks near an interface in several materials, including polymethylmethacrylate (PMMA), Nugget sandstone, and Indiana limestone. Results have shown that the mechanical properties of the interface relative to the properties of the materials on either side are important. A crack will not cross a well-bonded interface between two pieces of PMMA, even in the presence of a 13.79-MPa (2000-psi) normal load. Cracks will cross a well-bonded interface from PMMA to limestone, but not vice versa. Similarly, cracks will propagate across a bonded interface from Nugget sandstone to limestone, but not the other way. Pressure-driven cracks will cross an unbonded interface between limestone blocks at normal loads as low as 3.45 MPa (500 psi).

Experimental studies

“…The effects of in situ stress and the rock layer on the containment of a hydraulic fracture are extensively investigated by Warpinski et al [9], Teufel et al [10], and Hanson et al [11]. Jeffrey and Bunger [12] built a laboratory setup using transparent PMMA (PolyMethyl Methacrylatic Acid) blocks with machined surface profile, which when pressed against end-plates creates step-like stress profile that leads to fracture height containment.…”

“…Substituting of Eqs. (9)(10)(11)(12)(13)(14)(15)(16)(17), (9)(10)(11)(12)(13)(14)(15)(16)(17)(18), (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), and (9-20) into (9)(10)(11)(12)(13)(14)(15)(16) gives the fracture pressure decline equation as follows:…”

“…It is generally accepted that the minimum horizontal in situ stress can be reasonably approximated by the ISIP, that is, s Hmin ¼ ISIP (9)(10)(11)(12)(13)(14) It has been determined that an accuracy of AE30 psi can be achieved if the tests are properly conducted. For a cased wellbore, good perforations are essential for a clearly defined ISIP from the bottom-hole pressure record.…”

Modelling of hydraulic fracturing process by coupled discrete element and fluid dynamic methods

“…1989;Eslami J. 2010;Hanson et al 1980). However, while there are some studies dealing with modelling and simulation of rocks in the micro-scale (Gil 2005;Tomiczek 2003;Akram 2009;Potyondy 2004;Li 2001;Funatsu 2007;Kenneth et al 2013;Martinez 2012) the complex interplay between the micro-properties of a virtual sample and their corresponding effect on the material's behaviour during the calibration procedure provides a general guidance at best.…”

Recent Developments in Multiscale and Multiphase Modelling of the Hydraulic Fracturing Process

“…In subsurface investigations in particular, where heterogeneity and a wide range of complex inner mechanisms coexist, numerical modelling is necessary to represent real life scenarios. Numerous mathematical solutions have been applied to look, for example, into the critical mechanical parameters, such as the stress envelope, the porosity and permeability of the material and the effect of layering within the rock, or the way that these are influenced by the external mechanical load [42]. However, studies that employ modelling and simulation of rocks at the microscale [43][44][45] are fewer and their focus on the complex interplay between the microproperties and their corresponding effect on the material's behaviour during the calibration procedure provides at best a general guidance.…”