Microearthquakes induced by a hydraulic injection in sedimentary rock, East Texas

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In October, 1993, ARCO carried out a hydraulic injection near Beaumont, TX, into an unconsolidated sand, the Frio Formation. Fluid was injected into a 55m long zone at a depth of 1350 m. Four separate injections were done during 5 days. A total of more than 2.1 million gallons of bentonite slurry was injected, along with more than 3 million pounds of sand. Downhole fluid injection pressures ranged between about 3000 and 3500 psi. Induced microearthquakes were monitored by a set of 25 geophone packages situated in each of two monitoring well. More than 2400 microearthquakes were recorded during the ... continued below

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5 p.

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House, L.; Flores, R. & Withers, R. August 1, 1996.

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Description

In October, 1993, ARCO carried out a hydraulic injection near Beaumont, TX, into an unconsolidated sand, the Frio Formation. Fluid was injected into a 55m long zone at a depth of 1350 m. Four separate injections were done during 5 days. A total of more than 2.1 million gallons of bentonite slurry was injected, along with more than 3 million pounds of sand. Downhole fluid injection pressures ranged between about 3000 and 3500 psi. Induced microearthquakes were monitored by a set of 25 geophone packages situated in each of two monitoring well. More than 2400 microearthquakes were recorded during the injection, although most were too small to locate reliably using arrival times. A total of 54 microearthquakes were selected for detailed study. They were precisely located using arrival times of P and S phases from both of the monitoring boreholes. These locations are distributed non-uniformly, with a cluster near the injection borehole, a linear distribution about 200 m from the injection borehole, and a relatively quiet zone in between. The relatively nonseismic behavior in the middle zone compared to the other two zones suggests that this zone represent a discontinuity in the Frio Formation, although no obvious discontinuity has been identified from logs or nearby seismic reflection profiles. The large vertical extent of the geophone packages allowed an inversion of the arrival times for transverse isotropic elastic parameters, which yielded Vp anisotropy of about -13% and Vs of about -2%. Since these anisotropy values indicate that the vertical Vp and Vs are larger than the horizontal, they are surprising for this well bedded formation. Single-event focal mechanisms could be determined for 47 of the microearthquakes, and all are shear slip type. They show a large range of mechanisms, ranging from normal to reverse slip. Normal or oblique-normal slip predominant though, with T (tensional) axes generally nearly horizontal and approximately N-S. 3 refs., 4 figs., 1 tab.

Physical Description

5 p.

Notes

OSTI as DE96010933

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  • 1996 annual meeting of the Society of Exploration Geophysicists (SEG), Denver, CO (United States), 10-15 Nov 1996

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  • Other: DE96010933
  • Report No.: LA-UR--96-1379
  • Report No.: CONF-961134--2
  • Grant Number: W-7405-ENG-36
  • DOI: 10.2172/392753 | External Link
  • Office of Scientific & Technical Information Report Number: 392753
  • Archival Resource Key: ark:/67531/metadc686942

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  • August 1, 1996

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  • July 25, 2015, 2:20 a.m.

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  • Feb. 29, 2016, 9:50 p.m.

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House, L.; Flores, R. & Withers, R. Microearthquakes induced by a hydraulic injection in sedimentary rock, East Texas, report, August 1, 1996; New Mexico. (digital.library.unt.edu/ark:/67531/metadc686942/: accessed August 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.