Microseismic Monitoring of the Valhall Reservoir

Dyer, B.; Barkved, O. I.; Jones, R. H.; Folstad, P.G.; Rodriguez, S.

doi:10.3997/2214-4609.201407733

Cited by 4 publications

(3 citation statements)

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“…The method has been applied in developing hot dry rock reservoirs (e.g., Pine and Batchelor, 1984;House, 1987;Jones et al, 1995;Tezuka and Niitsuma, 2000) and has been demonstrated in oil and gas fields as a technique for mapping and calibrating stimulations (e.g., Phillips et al, 1998;Warpinski et al, 1998), monitoring waste injection (Keck and Withers, 1994), and delineating reservoir structures affected by production (e.g., Rutledge et al, 1998). Applications are becoming more routine with the availability of retrievable borehole receiver arrays (e.g., Dyer et al, 1999;Maxwell et al, 2002;Griffin et al, 2003). Beyond mapping gross structure and fluid-flow paths, relative source location techniques can also be applied to reservoir microseismicity to resolve discrete fracture geometry and aid in solving source mechanisms (e.g., Phillips et al, 1997;Phillips, 2000;Fehler et al, 2001;Rowe et al, 2002;Moriya et al, 2003), thereby providing more detailed information on how the forced fluid flow affects a reservoir's natural fractures.…”

Section: Introductionmentioning

confidence: 99%

Faulting Induced by Forced Fluid Injection and Fluid Flow Forced by Faulting: An Interpretation of Hydraulic-Fracture Microseismicity, Carthage Cotton Valley Gas Field, Texas

Rutledge¹,

Phillips²,

Mayerhofer³

2004

Bulletin of the Seismological Society of America

274

215

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We analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the Carthage gas field of east Texas. The treatments were conducted in two adjacent boreholes within interbedded sands and shales of the Upper Cotton Valley formation. The microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers. Events throughout all the treatments show strike-slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction. These events are consistent with the reservoir's prevalent natural fractures, known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orientation. When this uniform fracture system was activated exclusively, the detected shear deformation, measured as the moment release per unit volume of fluid injected, was constant, independent of various fluid viscosities and flow rates used. Within the base of the Upper Cotton Valley formation, anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones. The mechanisms are also strike-slip, but the fault planes are more favorably oriented for failure. The dense clusters show location patterns diverging in time, suggesting the expulsion of fluids from compressive fault jogs. Fluid flow forced by the adjacent slip-induced loading appears to initially extend the treatments, but the loading also tends to lock up and concentrate stress at the jogs, as evident by fewer but larger events populating the structures as treatments progress. As a result, effective drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs. These high-moment asperities are similar to dense patches of seismicity observed along creeping sections of the San Andreas fault, where they have been attributed to localized zones of strength or stress concentration, surrounded by larger regions undergoing stable, aseismic slip. This similarity, plus large moment deficits in terms of volume injected, suggests a large component of aseismic slip is induced by the Cotton Valley treatments.

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Section: Introductionmentioning

confidence: 99%

Faulting Induced by Forced Fluid Injection and Fluid Flow Forced by Faulting: An Interpretation of Hydraulic-Fracture Microseismicity, Carthage Cotton Valley Gas Field, Texas

Rutledge¹,

Phillips²,

Mayerhofer³

2004

Bulletin of the Seismological Society of America

274

215

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“…The aims, experimental design and results of the Valhall microseismic experiment are reported by Dyer et al (1999). Shear‐wave splitting analysis of the Valhall microseismic data is described in detail by Teanby et al (2004).…”

Section: Introductionmentioning

confidence: 99%

“…Over a period of 56 days microseismic events were continuously recorded yielding a data set of 572 events, 324 of which could be located reliably (Dyer et al 1999). The majority of the events were located, above the reservoir, in the siltstone caprock at about 2 km depth, 300–500 m from the receivers.…”

Section: Introductionmentioning

confidence: 99%

Attenuation anisotropy and the relative frequency content of split shear waves

Carter¹,

Kendall²

2006

Geophysical Journal International

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S U M M A R YThe variation of frequency-dependent seismic wave attenuation with direction (attenuation anisotropy) contains additional information to that contained in velocity anisotropy. In particular, it has the potential to distinguish between different mechanisms that can cause velocity anisotropy. For example, aligned fracturing might be expected to cause measurable velocity and attenuation anisotropy, while preferred crystal orientation leads to significant velocity anisotropy but may cause only small amounts of attenuation. Attenuation anisotropy may also contain useful information about pore-fluid content and properties. We present a methodology for analysis of attenuation anisotropy, and apply it to a microseismic data set previously analysed for shear-wave splitting by Teanby et al. (2004). Attenuation anisotropy values obtained show a temporal variation which appears to correlate with the temporal variation in the velocity anisotropy. The comparison of the relative frequency content of fast (S1) and slow (S2) split shear waves is a convenient method for examining seismic attenuation anisotropy. Provided that S1 and S2 initially have the same spectral colouring, that no spectral distortion is introduced by the differences between receiver responses of geophone components, and that spectral distortion due to background noise can be ignored or corrected for, we can attribute any differences in their frequency content to attenuation anisotropy. Attenuation anisotropy, where present, should be detected by the different (approximately orthogonal) polarizations of S1 and S2 as they pass through the anisotropic medium. In the presence of attenuation anisotropy S1 and S2 should experience different levels of frequency-dependent attenuation. We quantify the differential attenuation of S1 and S2 using a scheme based on a spectral ratio method. We present results from a microseismic data set acquired in an abandoned oil well at Valhall, a North Sea oil field. The results are surprising in that sometimes the slower arrival, S2, is richer in high frequencies than the faster, S1. This appears to be contrary to results predicted by theoretical crack models for attenuation anisotropy (e.g. Hudson 1981). The mechanism responsible for these observations is not clear. Our differential attenuation attribute correlates with the angle between the strike of the inferred initial shear-wave source polarization and the fast shear-wave polarization, which suggests that the split shear wave with the larger amplitude is preferentially attenuated. Our attribute also correlates with the event backazimuth, and the minimum percentage anisotropy.

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Microseismic Technology

Duncan¹

2021

Integration of Geophysical Technologies in the Petroleum Industry

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Microseismic Monitoring of the Valhall Reservoir

Cited by 4 publications

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Faulting Induced by Forced Fluid Injection and Fluid Flow Forced by Faulting: An Interpretation of Hydraulic-Fracture Microseismicity, Carthage Cotton Valley Gas Field, Texas

Faulting Induced by Forced Fluid Injection and Fluid Flow Forced by Faulting: An Interpretation of Hydraulic-Fracture Microseismicity, Carthage Cotton Valley Gas Field, Texas

Attenuation anisotropy and the relative frequency content of split shear waves

Microseismic Technology

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