Stress Estimation
The lithology and stress regime of the reservoir determine the best locations for successful hydraulic fracturing, but these can vary significantly over short distances. CGG has developed a method of estimating rock strength and stress between wells using 3D seismic data.
Calculation of the Differential Horizontal Stress Ratio (DHSR - the differential ratio of the maximum and minimum horizontal stresses) from seismic and inversion for rock properties can be used to identify areas for successful fracking. The most extensive fracture networks are produced where the rock is brittle and there is little differential stress.
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Color background shows dynamic Young’s Modulus estimated from seismic. “Plates” (indicated by the arrow) show the differential horizontal stress ratio (DHSR). The size of the plate is proportional to the magnitude of the DHSR and the direction of the plate shows the direction of the local maximum horizontal stress. |
Seismic Solutions
The use of 3D seismic can maximize the production from hydraulic fracturing:
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Seismic can provide rock strength information, from Young's modulus and Poisson's ratio.
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Vertical stress can be estimated from density, which can be calculated from the AVO of long offset data, as well as from multicomponent data.
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Differential horizontal stresses can be estimated from azimuthal anisotropy measurements which require wide-azimuth data. Calibrated minimum and maximum horizontal stresses can then be derived, allowing estimation of the DHSR and closure stress.
Combining these stress estimates with Young's modulus provides a good estimate of how hydraulic fracturing will behave:
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Where there is high Young’s modulus (more brittle) and low DHSR, fracture swarms are more likely to occur.
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Where there is high Young’s Modulus and high DHSR aligned fractures are more likely to occur.
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Where there is low Young's Modulus hydraulic fracturing won’t work because the rock is too ductile.
The success of the frac job and distribution of the induced fractures can be monitored using microseismic.
