Fracturing Gels as Analogs to Understand Fracture Behavior in Shale Gas Reservoirs
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ORIGINAL PAPER
Fracturing Gels as Analogs to Understand Fracture Behavior in Shale Gas Reservoirs Zheng Li1 · Jingyi Wang1 · Ian D. Gates1 Received: 23 October 2019 / Accepted: 19 May 2020 © The Author(s) 2020
Abstract Hydraulic fracturing is widely used in the exploitation of unconventional reservoirs, such as shale gas and tight gas. However, a full understanding of the activation of natural fractures, prediction of fracture growth, distribution of proppant, and network fracture system effectiveness remain unresolved. The onset of fracturing in the media requires energy and this is due to the buildup of pressure within the rock due to continuous injection of fluid. In other words, when the energy associated with the injection fluid reaches the fracture strength of the rock, the fracture initiates and propagates into the formation. Here, we use gelatin in hydraulic fracturing laboratory tests and compare the results to a modified radial hydraulic fracturing theory. The mechanics of the gelatin, procedures to make a testing gelatin block, and procedures to conduct the test are described. The results show that the fracture evolving behaviours from experiments are well matched by the theory. The results are then scaled up to understand fracture growth behaviour in a tight rock reservoir. Keywords Hydraulic fracturing · Unconventional oil and gas · Tight gas · Shale gas · Fracture model · Experimental fracturing · Gelatin
1 Introduction Hydraulic fracturing is widely used to produce petroleum from unconventional reservoirs, such as shale and tight gas reservoirs (Rahm 2011; Rutqvist et al. 2013; Arthur et al. 2009; Cipolla et al. 2010; Olson 2008; Warpinski 1991,1990; Rodgerson 2000; Gregory et al. 2011). Generally, these kind of reservoirs have extremely low permeabilities and are impossible to produce economically without effective stimulation such as hydraulic fracturing. There are many reports in the literature on hydraulic fracturing experiments in the laboratory (Zoback et al. 1977; Blanton 1982; Teufel and Clark 1981; Jaworski et al. 1981; Matsunaga et al. 1993; Potluri et al. 2005; Lockner 1993) and in general, these experiments are used to determine the nature of rock fracturing, propagation of fractures, and geomechanical properties of the rock. One of the key concerns facing hydraulic fracturing operations is the ability to model these
* Ian D. Gates [email protected] 1
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB, Canada
systems and validate these models using experiments or field observations on the route to build predictive models. In typical practice, computer-based models are calibrated to field operations and these history-matched models are then used to predict fracturing operations at other stages or other wells. However, it is well-known that most models are not predictive given the uncertainties of the geological and geomechanical properties, the assumptions taken to construct the model, and approximations invoked using the numerical method. H
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