The data describing the stress field normally includes either direct in-situ measurements in the wellbore, or indirect data – focal mechanisms of microearthquakes in the area of interest. Joint inversion of the source mechanisms and various types of borehole data allows recovering of both principal stress directions and magnitudes. A combination of data from reservoir injections and focal mechanisms from induced microseismicity allow reconstruction of the full stress tensor: stress orientation and principal stress magnitudes. Ultimately, the full stress tensor together with the focal mechanisms provide an estimate of pore pressure at the location of every event, which can be mapped in time and space. We successfully apply joint stress inversion to a Barnett shale hydraulic fracturing dataset and demonstrate pore pressure mapping.


Determination of the stress field in rock is of utmost importance in underground energy extraction, including shale hydrocarbons production and geothermal. Various methods have been proposed for solving this problem. Generally, they can be divided into two groups: direct stress measurements in the borehole and different stress inversion techniques based on focal mechanisms of earthquakes in the area of interest. The first group includes: leak-off tests (LOT) and measurements of instantaneous shut-in pressure (ISIP) both constrain the minimum principal stress (Zoback et al., 2003); hydraulic tests on pre-existing fractures (HTPF) yield the normal stress acting on a given fracture; wellbore breakout and elongation analysis constrain the principal stress directions (e.g., Zoback et al., 1985). Several methods for the focal mechanisms inversion were proposed by different researchers (Angelier et al., 1990; Gephart et al., 1984; Michael 1987). These methods yield orientation of the stress and ratio of the principal stress magnitudes. They rely on different assumptions and may or may not require fault plane selection prior to the inversion. However, most of the inversion techniques assume a homogeneous stress field without depth-dependency, which is the largest source of stress heterogeneity.

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