- Neal Borden Nagel (Itasca Houston, Inc.) | Ivan Gil (Itasca Houston) | Marisela Sanchez-nagel (Itasca Houston,inc.) | Branko Damjanac (Itasca Consulting Group)
- Document ID
- Society of Petroleum Engineers
- SPE Hydraulic Fracturing Technology Conference, 24-26 January, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 5.8.1 Tight Gas, 5.5 Reservoir Simulation, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 3 Production and Well Operations, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.8.6 Naturally Fractured Reservoir, 5.9.2 Geothermal Resources, 4.3.4 Scale, 5.8.2 Shale Gas, 5.5.3 Scaling Methods, 4.6 Natural Gas, 1.2.2 Geomechanics, 2.5.1 Fracture design and containment, 2 Well Completion, 6.5.1 Air Emissions
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With the huge growth in the stimulation of naturally fractured formations, it is clear that the industry needs new hydraulic fracturing simulation tools beyond the limits imposed by pseudo3D fracturing model. Discrete element models (DEM), in which both matrix block behavior and fracture behavior are explicitly modeled, offer one option for the specific modeling of hydraulic fracture creation and growth in naturally fractured formation without, for example, the assumption of bi-planar fracture growth.
In this paper, we show the results of the successful realistic simulations of fluid injection into a given NFR using the 3DEC DEM model. The simulations included coupled fluid flow-deformation analysis, failure type and extent calculations, as well as a series of parametric analyses. The parameters investigated included: 1) injection rate and its effect on the overall injection results, and 2) fluid viscosity, which had a significant influence on the ratio of tensile (mode 1) failure versus shear failure.
According to a US Department of Energy-commissioned report (GWPC, 2009), the United States contains 1,744 tcf of technically recoverable natural gas. Of this, nearly 60% of the onshore recoverable resource (Navigant Consulting, 2008) is in unconventional plays (shale gas, tights sands, and coalbed natural gas). In separate reports (Medlock III, 2010 and Kuuskraa and Stevens, 2009), the estimated technically recoverable US shale gas resource ranged from 583 to 715 tcf. One tcf of gas is sufficient to heat 15 million homes for a year or generate 100 billion kilowatt-hours of electricity at a 30-50% reduction in CO2 emissions as compared to fuel oil or coal (GWPC, 2009). Given these statistics, and similar statistics on a global basis (Rogner, 1997), it is clear that shale gas developments will play an important role in meeting the world's energy needs well into the 21st century.
While shale gas has been produced since 1821 (Harper, 2008), and the Antrim shale has produced gas for decades, it is only since the late 90s, with the development of the Barnett shale that shale gas production has become significant (Navigant Consulting, 2008). The significant keys to the increase in shale gas production have been the application of horizontal wells, the application and improvements in hydraulic fracturing, and significant natural gas prices (GWPC, 2009).
Hydraulic fracturing is key to shale gas developments because of the low to ultra-low permeability (Frantz and Jochen, 2005 and Harper, 2008). Equally important, the presence of natural fractures is often critical to the production of gas (Lancaster et al., 1996 and Chong et al., 2010) and these natural fractures and other planes of weakness can result in complex fracture geometries resulting from both tensile and shear rock failure (Palmer et al., 2010). As King (2010) has noted, the presence and ability to open and maintain flow in both primary and secondary natural fracture systems are keys to shale gas production. Furthermore, King (2010) notes that there are many commercial fracture simulators, developed primarily for sandstones, that assume bi-planar fracture development under reasonably constant leakoff that do not address the influence of shale frac leakoff into fissures and cracks.
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