**Microseismic Monitoring Developments in Hydraulic Fracture Stimulation**

Mirko van der Baan, David Eaton and Maurice Dusseault

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/56444

### **Abstract**

The last decade has seen a significantly increased interest in microseismic monitoring by the hydrocarbon industry due to the recent surge in unconventional resources such as shale-gas and heavy-oil plays. Both hydraulic fracturing and steam injection create changes in local pore pressures and in situ stresses and thereby brittle failure in intact rock plus additional slip/shearing in naturally fractured rock. Local rock failure or slip yields an acoustic emis‐ sion, which is also known as a microseismic event. The microseismic cloud represents thus a volumetric map of the extent of induced fracture shearing, opening and closing. Microseis‐ mic monitoring can provide pertinent information on in situ reservoir deformation due to fluid stimulation, thus ultimately facilitating reservoir drainage. This paper reviews some of the current key questions and research in microseismicity, ranging from acquisition, proc‐ essing to interpretation.

### **1. Introduction**

Microseismic events are very small earthquakes of generally negative moment magni‐ tude1 that are often associated with hydraulic fracturing or fluid flow in reservoirs. Build‐ ing upon long-standing applications of microseismic methods, such as monitoring of stability in underground mines (e.g., Gibowicz and Kijko, 1994; Urbancic and Trifu, 2000)

<sup>1</sup> Earthquake magnitude is measured on a logarithmic scale. Various roughly equivalent amplitude-based magnitude scales are in use, of which moment magnitude is the most general.

© 2013 van der Baan et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and enhanced geothermal systems (e.g., Häring et al., 2008), microseismic monitoring techniques are being used increasingly by the oil and gas industry to monitor hydraulic stimulation of "tight" (very low permeability) hydrocarbon reservoirs and steam injection into heavy-oil fields. As such, it is one of the technologies underpinning the recent up‐ swing of oil production in Western Canada, as well as the development of new tight-gas fields, monitoring of caprock integrity during in situ heavy-oil exploitation, and carbon capture and storage (McGillivray, 2005; Maxwell et al., 2010; Verdon et al., 2010; Maxwell, 2011; Clarkson et al., 2011).

shale-gas plays in North America. It is clear that tight-gas and shale gas will remain an important resource for many years to come and further technological improvements will enable economic drainage of additional reservoirs. One of these emerging technologies is

Microseismic Monitoring Developments in Hydraulic Fracture Stimulation

http://dx.doi.org/10.5772/56444

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**Figure 1.** Current shale plays in North America. Source: EIA http://www.eia.gov/pub/oil\_gas/natural\_gas/analy‐

Hydraulic fracturing (also known as fraccing or fracking) leads to brittle failure inside a reservoir, which is typically accompanied by microseismicity. Microseismicity refers to discrete rock-deformation events, analogous to tiny earthquakes, that are generally of moment magnitude < 0. For reference, magnitude 0.2 is the equivalent of the energy released by a large hand grenade (30 g TNT equivalent), whereas a typical small mining blast has a magnitude around 1-1.5, corresponding to 2-2.5kg of TNT. Since magnitude scales are logarithmic, negative magnitude events thus correspond to the energy yield equivalent of milligrams or

Monitoring of microseismic activity is a geophysical remote-sensing technology that provides the ability to detect and map associated fracturing processes, either in real-time or in postprocessing mode. A typical field deployment involves the installation of an array of continu‐

microseismic monitoring.

sis\_publications/maps/maps.htm

even micrograms of TNT.

This paper reviews some of the current questions and research in microseismicity, ranging from acquisition, processing to interpretation. However, before reviewing these aspects, it is important to consider the wider context first and the economic impact of hydraulic fracturing in tight-hydrocarbon fields.
