Microseismic imaging of hydrofractures with the aid of conical waves

Ilderton, D. C.; Patzek, Tadeusz W; Rector, James W.; Vinegar, Harold J

doi:10.1190/1.1822457

Cited by 2 publications

(1 citation statement)

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“…Monitoring hydraulic fracturing is important because it helps optimize the stimulation process and in assessing the hazards which might be generated from induced seismicity. Conventional monitoring techniques involve methods of hypocenter event relocation (Rutledge and Phillips, 2003), moment tensor inversion for source mechanism (Nolen-Hoeksema and Ruff, 1999;Song and Toksoz, 2011), and travel time tomography for velocity and anisotropy parameter estimation (Idelton et al, 1993). Neither of those techniques address the explicit imaging of the fractures in the vicinity of the stimulation.…”

Section: Introductionmentioning

confidence: 99%

Seismic imaging of hydraulically-stimulated fractures: A numerical study of the effect of the source mechanism

Shabelansky

Malcolm

Fehler

et al. 2012

SEG Technical Program Expanded Abstracts 2012

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SUMMARYWe present a numerical study of seismic imaging of hydraulically stimulated fractures using a single source from an adjacent fracturing-process. The source is either a point force generated from the perforation of the casing of the well or a double-couple as is typically observed from the induced microseismicity. We assume that the fracture is sufficiently stimulated to be imaged by reflected seismic energy. We show for a specific monitoring geometry of hydrofracturing that not only different waves (P and S) but also different source mechanisms from the same region form an image of different parts of the target fracture and thus add complementary information. The strategy presented here might be used as an additional monitoring tool of the hydrofracturing process.

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Section: Introductionmentioning

confidence: 99%

Seismic imaging of hydraulically-stimulated fractures: A numerical study of the effect of the source mechanism

Shabelansky

Malcolm

Fehler

et al. 2012

SEG Technical Program Expanded Abstracts 2012

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Passive Imaging of Hydrofractures in the South Belridge Diatomite

Ilderton¹,

Patzek²,

Rector³

et al. 1996

SPE Formation Evaluation

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Summary We present the results of a seismic analysis of two hydrofractures spanning the entire diatomite column (1110-1910 ft or 338-582 m) in Shell's Phase II steam drive pilot in South Belridge, California. These hydrofractures were induced at two depths (1110-1460 and 1560-1910 ft) and imaged passively using the seismic energy released during fracturing. The arrivals of shear waves from the cracking rock ("microseismic events") were recorded at a 1 ms sampling rate by 56 geophones in three remote observation wells, resulting in 10GB of raw data. These arrival times were then inverted for the event locations, from which the hydrofracture geometry was inferred. A five-dimensional conjugate-gradient algorithm with a depth-dependent, but otherwise constant shear wave velocity model (CVM) was developed for the inversions. To validate CVM, we created a layered shear wave velocity model of the formation and used it to calculate synthetic arrival times from known locations chosen at various depths along the estimated fracture plane. These arrival times were then inverted with CVM and the calculated locations compared with the known ones, quantifying the systematic error associated with the assumption of constant shear wave velocity. We also performed Monte Carlo sensitivity analyses on the synthetic arrival times to account for all other, random errors that exist in field data. After determining the limitations of the inversion algorithm, we hand-picked the shear wave arrival times for both hydrofractures and inverted them with CVM. Finally, to correct for the areal inhomogeneity of the rock, we calculated the distortion of conical waves that were generated by air gun blasts in a remote observation well. This novel technique improved significantly the accuracy of the event locations in the shallow hydrofracture. The azimuth of both hydrofractures was N21 4 E. In each treatment well, there were two separate hydrofractures at two different depths that correspond to the diatomite layers with higher permeabilities. Both shallow hydrofractures were asymmetrical. Initially, the upper, NE wing was 230 ft long, whereas the lower SW wing was only 30 ft long. The deep hydrofracture was symmetrical and the wings of its two parts were initially 130 and 10 ft long, respectively. These conclusions agree well with temperature surveys in the surrounding observation wells during steam injection. Introduction The late and middle Miocene diatomaceous oil fields in the San Joaquin Valley, California, are located in Kern County, some forty miles west of Bakersfield. The largest oil volumes are found in the South, Middle and North Belridge Diatomite and Brown Shale, Lost Hills Diatomite and Brown Shale, Antelope Hills, McDonald Anticline, Chico-Martinez Chert, Cymric Diatomite, McKittrick, Railroad Gap, Belgian Anticline, Asphalto, Elk Hills, Buena Vista Antelope Shale, and Midway Sunset Reef Ridge and Antelope Shale. The major producers of diatomite oil are Shell, Mobil, Chevron, Santa Fe, Crutcher Tufts, Exxon, Texaco, and Unocal. An estimated original-oil-in-place in the Monterey diatomaceous fields exceeds 10 billion barrels and is comparable to that in Prudoe Bay in Alaska.

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Microseismic imaging of hydrofractures with the aid of conical waves

Cited by 2 publications

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Seismic imaging of hydraulically-stimulated fractures: A numerical study of the effect of the source mechanism

Seismic imaging of hydraulically-stimulated fractures: A numerical study of the effect of the source mechanism

Passive Imaging of Hydrofractures in the South Belridge Diatomite

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