Reservoir Fracture Mapping Using Microearthquakes: Two Oilfield Case Studies

Phillips, W. S.; Rutledge, James; Fairbanks, Thomas D.; Gardner, T.L.; Miller, M.E.; Schuessler, B.K.

doi:10.2118/36651-pa

Cited by 15 publications

(8 citation statements)

References 29 publications

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“…In the sections below, we first report the development of a geomechanical model that includes knowledge of the magnitude and orientation of principal stresses, the existence and orientation of natural fractures and faults, and the mechanical properties of the formations being produced. Knowledge of the stress field can be used to better understand microseismic events and fracture networks resulting from hydraulic fracture stimulation (Fehler et al, 1987;Phillips et al, 1998;Rutledge et al, 1998;Maxwell et al, 2002). Therefore, linking observations of microseismic data with geologic and geophysical information can help us better understand the geomechanical properties of the Bakken Formation and the role of preexisting fractures and faults on the effectiveness of hydraulic fracturing stimulation in this reservoir.…”

Section: Introductionmentioning

confidence: 99%

The role of preexisting fractures and faults during multistage hydraulic fracturing in the Bakken Formation

Yang

Zoback

2014

Interpretation

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We performed an integrated study of multistage hydraulic fracture stimulation of two parallel horizontal wells in the Bakken Formation in the Williston Basin, North Dakota. There are three distinct parts of this study: development of a geomechanical model for the study area, interpretation of multiarray downhole recordings of microseismic events, and interpretation of hydraulic fracturing data in a geomechanical context. We estimated the current stress state to be characterized by an NF/SS regime, with S H max oriented approximately N45°E. The microseismic events were recorded in six vertical observation wells during hydraulic fracturing of parallel wells X and Z with three unusual aspects. First, rather than occurring in proximity to the stages being pressurized, many of the events occurred along the length of well Y, a parallel well located between wells X and Z that had been in production for approximately 2.5 years at the time X and Z were stimulated. Second, relatively few fracturing stages were associated with an elongated cloud of events trending in the direction of S H max as was commonly observed during hydraulic fracturing. Instead, the microseismic events in a few stages appeared to trend approximately N75°E, approximately 30°from the direction of S H max . Earthquake focal plane mechanisms confirmed slip on faults with this orientation. Finally, the microseismic events were clustered at two distinct depths: one near the depth of the well being pressurized in the Middle Bakken Formation and the other approximately 800 ft above in the Mission Canyon Formation. We proposed that steeply dipping N75°E striking faults with a combination of normal and strike-slip movement were being stimulated during hydraulic fracturing and provided conduits for pore pressure to be transmitted to the overlaying formations. We tested a simple geomechanical analysis to illustrate how this occurred in the context of the stress field, pore pressure, and depletion in the vicinity of well Y.

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Section: Introductionmentioning

confidence: 99%

The role of preexisting fractures and faults during multistage hydraulic fracturing in the Bakken Formation

Yang

Zoback

2014

Interpretation

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“…If successful, we anticipate testing flow models against pressurization and tracer data that have been collected at Fenton Hill. Results from the well-constrained experiment at Fenton Hill may help to interpret seismicity in other situations in which high-pressure fluids are or may be important, such as oil and gas reservoirs [e.g., Warpinski et al, 1996;Keck and Withers, 1994;Phillips et al, 1996], fault zones [Johnson andMcEvilly, 1994, 1995], and volcanic environments [e.g., Fremont and Malone, 1987].…”

Section: Introductionmentioning

confidence: 99%

Detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters

Phillips¹,

House²,

Fehler³

1997

J. Geophys. Res.

100

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Abstract. Microearthquake clusters form distinct, plavar patterns within five study regions of a geothermal reservoir undergoing hydraulic fracturing at Fenton Hill, New Mexico. The patterns define individual, slipping joint surfaces of dimension 40-120 m, containing 80-150 events each. Sharp, straight edges truncate the clusters; we interpret these as marking intersections with aseismic joints. Each edge orientation is consistent with an intersection between the active joint and a plane oriented parallel to one of the other clusters we identify. Therefore it appears that cluster shapes constrain the geometry of seismic and aseismic joints; both could be important components of the fluid-flow network. The distribution of inferred slip plane orientations is consistent with but fails to provide sufficient constraint to differentiate conclusively between two, very different, stress field estimates, one measured using pressurization and wellbore breakouts, the other using focal mechanisms of the largest microearthquakes. An impermeable joint model, requiring pore pressure in excess of the normal stress on a joint before slip can occur, was inconsistent with many of the inferred slip plane orientations. The high-quality locations were possible because events from the same cluster generated nearly similar waveforms, permitting the precise determination of relative arrival times. Standard deviations of arrival-time residuals fall between 0.1 and 1.1 ms for these clusters. Major axes and aspect ratios of the 90% confidence ellipsoids range from 6 to 28 rn and 1.5 to 8, respectively. Small events dominate the seismic energy release and thoroughly populate the identified, active joints, allowing the hypocenters to reflect details of the joint structure. To further investigate the reservoir structure, we applied a source-array, slant-stack technique to waveforms from the well-located clusters, yielding directions that scattered energy left each cluster. By studying paths of scattered waves we expected to pinpoint impedance contrasts that might have indicated concentrations of fluid-filled joints. However, results show that scattered energy in the S wave coda left the source region in the same direction as the direct S wave. Direct waves may have excited borehole tube waves that became trapped in the vicinity of the geophone tool, overwhelming any energy scattered from the reservoir.

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“…In addition, microseismicity are recorded for few hours after the cease of injection while only few events are encountered during the following weeks of the treatment. In a six months monitoring program by Reference [27] to evaluate the seismicity associating oil production from a tight carbonate reservoir (2% porosity), post a successful hydraulic fracturing job, a total 3200 events of average Mw = −1.2 were recorded during the production of a total of 1250 m 3 of oil (Figure 7). The recorded microseismicity during this monitoring program was practically restricted to the stimulated reservoir horizon which indicates a direct relation to recovered-oil production.…”

Section: Microseismicity and Treatment Parametersmentioning

confidence: 99%

“…This change in the stimulated reservoir volume is attributed to the reservoir rock competency and durability. Competent rocks favor the development of a single fracture over long distance but durable rocks (highly fractured), prefer fracture propagation over large area rather than long distance [23] [27]. The energy infused into the formation could be dispensed either as numerous micro-fractures or displacement along a fault plane with distinct microseismic record describing each case.…”

Section: Microseismicity and Treatment Parametersmentioning

confidence: 99%

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Evaluation of Microseismicity Related to Hydraulic Fracking Operations of Petroleum Reservoirs and Its Possible Environmental Repercussions

Abdulaziz¹

2014

OJER

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Petroleum reservoir operations such as oil and gas production, hydraulic fracturing, and water injection induce considerable stress changes that at some point result in rock failure and emanation of seismic energy. Such seismic energy could be large enough to be felt in the neighborhood of the oil fields, therefore many issues are recently raised regarding its environmental impact. In this research we analyze the magnitudes of microseismicity induced by stimulation of unconventional reservoirs at various basins in the United States and Canada that monitored the microseismicity induced by hydraulic fracturing operations. In addition, the relationship between microseismic magnitude and both depth and injection parameters is examined to delineate the possible framework that controls the system. Generally, microseismicity of typical hydraulic fracturing and injection operations is relatively similar in the majority of basins under investigation and the overall associating seismic energy is not strong enough to be the important factor to jeopardize near surface groundwater resources. Furthermore, these events are less energetic compared to the moderately active tectonic zones through the world and usually do not extend over a long period at considerably deep parts. However, the huge volume of the treatment fluids and improper casing cementing operation seem to be primary sources for contaminating near surface water resources.

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Reservoir Fracture Mapping Using Microearthquakes: Two Oilfield Case Studies

Cited by 15 publications

References 29 publications

The role of preexisting fractures and faults during multistage hydraulic fracturing in the Bakken Formation

The role of preexisting fractures and faults during multistage hydraulic fracturing in the Bakken Formation

Detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters

Evaluation of Microseismicity Related to Hydraulic Fracking Operations of Petroleum Reservoirs and Its Possible Environmental Repercussions

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