Microseismicity

Sherburn, S., Allis, R. Clotworthy, A. 1990. Microseismic activity at Wairakei and Ohaaki geothermal fields. In Proceedings 12th New Zealand Geothermal Workshop, University of Auckland, 51-55. 

We have drilled two 4000-ft-deep exploratory holes at a site about 30 miles east of Garlsbad and 40 miles southwest of Hobbs. Hydrological tests have been made, and geophysical logs of both holes were taken. Gores were recovered for mineralogical studies and physical properties measurements. Additional investigations under way in New Mexico include a local microseismic study, and appraisals of the oil and potash potentials of the area of interest. 

Is sand bursting in conventional wells and shear events in conventional wells chaotic Is it linked to stress redistributions and how do we predict longterm behavior Microseismic monitoring could help quantify these mechanical coupling issues. 

Microseismic monitoring is currently the best available method for obtaining three-dimensional information about reservoirs and fracture systems at locations remote from boreholes. The primary problem of the method is its location accuracy. When located with conventional location algorithms, the events are frequently seen to be distributed as a cloud with little macro- or microstructure. It is difficult to meaningfully correlate such images with logging data of existing wells. Therefore, information on detailed reservoir structure, fracture orientation, and hydraulic behavior cannot be obtained from the application of conventional microseismic location techniques. 

This paper overviews the high resolution microseismic mapping techniques and discusses a... 

Figure 1 Results of collapsing (right) and conventional nuipping (left) for microseismicity in Mammoth Lake, USA, by Jones (1998).

The clustering analysis is another mean to find and evaluate structures in seismic clouds. Phillips et al, (1997) and Phillips (2000) proposed a repicking method, which produces the relative time difference of phases within a group of similar microseismic events, followed by master event relative source locations. For this analysis, waveforms are lined up after low pass filtering, with P- and S-wave arrival times are manually repicked from a similar portion of the waveform. The technique can be used to identify wave arrival times and improve the accuracy of relative source location determinations. Phillips (2000) applied this analysis to microseismic clouds created by hydraulic stimulation in the Soultz HDR reservoir and delineated two distinct intersecting planar structures. 

Induced microseismic activity was detected using three downhole 4-component detectors and one hydrophone, installed in wells 4550, 4616, 4601 and EPSl in the 1993 experiment. The 4-componet detector consists of accelerometers mounted in a housing and set in sand at the bottom of the borehole. The three 4-component seismic detectors and hydrophone were set at depths of 1,500 m, 1,420 m, 1,600 m and 2,850 m, respectively. 

Figure 8 shows a result of the multiplet-clustering analysis applied to the multiplet groups in the microseismic structure shown in Figure 3. The 97 multiplet clusters are plotted in this figure. Relative locations between clusters are determined with error less than 6 m, while the location error for the JHD (Joint Hypocenter Determination) mapping shown in Figure 3 is about IS m.

HDR/HWR geothermal development. These techniques have been applied to the microseismic data set obtained during the hydraulic stimulation at Soultz HDR field, France, in 1993. Detailed seismic structure of a seismic line, which was growing linearly at the early stage of the stimulation, has been analysed. It is estimated that this structure shows enhanced permeable paths and consist of sub parallel microstructures, which are oriented to the directions most easy to slip by the stimulation. 

Evans, K. F., Jones, R., Soma, N. and Baria, R. (1999). Correlation of near-borehole microseismic structures defined by the collapsed cloud of events induced by the 1993 GPKl stimulation with flowing fractures.. Internal Report of MURPHY Project 1999, NEDO. 

Jones, R. H., Beauce, A., Jupe, A., Fabriol, H. and Dyer, B. C. (1995). Imaging induced microseismicity during the 1993 injection tests at Soultz-sous-Forets, France. Proc. World Geothermal Congress 1995, Vol. 4, 2665-2669. 

Moriya, H., Nakazato, K., Evans, K. F., Niitsuma, H., Jones, R.H. and Baria, R. (2001). Evaluation of the Soultz HDR system by precise mapping techniques of induced microseismic event. Trans. Geothermal Resources Council 2000, Vol. 25, 187-190. 

Tezuka, K. and Niitsuma, H. (1997). Integrated interpretation of microseismic clusters and fracture system in a hot dry rock artificial reservoir. Expanded Abstr., SEG 67 Ann. Intern. Meeting. 

ESTIMATION OF CRITICAL PORE PRESSURE FOR SHEAR SLIP OF FRACTURES AT THE SOULTZ HOT DRY ROCK GEOTHERMAL RESERVOIR USING MICROSEISMIC MULTIPLETS... 

In this paper, we suggest a method for estimation of pore-pressure during hydraulic stimulation of geothermal reservoir by using the induced microseismic multiplets. The results of the application to the microseismic events at Soultz field are demonstrated showing the feasibility of the method. 

The multiplet-clustering analysis is a method to estimate relative positions of the multiplet clusters as well as the relative source locations within individual multiplets (Moriya et al., 2CK)3). We have applied the multiplet-clustering analysis to the induced microseismic events as following procedures. 

Figure 2. Source locations of induced microseismic events, where the events...

It is considered that some fractures opened with increasing pore-pressure maybe after shear slip because the maximum wellhead pressure is about lOMPa. However, Mode I fractures can not radiate seismic events having enough energy, and we can not detect these seismic events. Therefore, we consider only shearing fractures for estimation of critical pore-pressure using induced microseismic events. 

Through observation of induced microseismic events and examination of well logging data, it has been understood that the permeable zone seems to be created by migration of shearing joints during hydraulic fracturing test, and that microseismic multiplets is considered to be seismic events associated with shearing of fractures which are favourably oriented to stress field. 

R. 2002. Detailed fracture system of the Soultz-sous-Forets HDR field evaluated using microseismic multiplet analysis. Pure Appl. Geophys., 159 pp.517-541. 

R. H., Borchers, B. Fehler, M. C. 2002. Using Automated high-precision repicking to improve delineation of microseismic structures at the Soultz geothermal reservoir. Pure Appl. Geophys, 159 pp.563-596. 

Xia Y X. et al. 2011. Study of the lead abutment pressure distribution base on microseismic monitoring[J]. Journal of China Coal Society 40 868-73. 

Xia Yong-Xue, Lan Hang, Wei Xiang-Zhi. 2011. Study of comprehensive evaluation technology for rock burst hazard based on microseismic and underground sound monitoring. Journal of China Coal Society, 36(s2) 358 364. 

Fujii Y, Ishijima Y, Deguchi G. 1997. Prediction of coal face rockbursts and microseismicity in deep longwall coal mining. International Journal of Rock Mechanics and Mining Sciences 34(1) 85-96. 

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