Locating Events using Borehole Microseismic Monitoring by Inclusion of Particle Motion Analysis

Transcription

1 Locating Events using Borehole Microseismic Monitoring by Inclusion of Particle Motion Analysis Balikpapan, October 5th-8th, 2015 REXHA VERDHORA RY Geophysical Engineering Institut Teknologi Bandung ANDRI DIAN NUGRAHA Global Geophysics Group Institut Teknologi Bandung SRI WIDIYANTORO Global Geophysics Group Institut Teknologi Bandung

2 Locating Events using Borehole Microseismic Monitoring by Inclusion of Particle Motion Analysis Presenter : Rexha Verdhora Ry Photo Company : Institut Teknologi Bandung Education Background : - Bachelor Degree (ITB), Geophysical Engineering - Master Degree (ITB), (on progress) Geophysical Engineering Working Experience : Research Assistant at LAPI ITB

3 Outline BACKGROUND PROCESSING DISCUSSION CONCLUDE REMARKS

4 Background (1) Microseismic monitoring around hydrocarbon reservoirs provides insight into induced deformation related to hydraulic fracturing. A single vertical array of seismometer in a borehole can constrain the depth of sources much better that surface seismometer. High cost, but effective and robust to map fracturing in layering features at certain depth. However in the case of all the sensors being deployed in a nearvertical borehole, there is a high ambiguity in the source location.

5 Background (2) N Misfit function = hypocenter of source = monitoring seismometer

6 Background (3) Borehole Seismometer -550 Depth (m) = hypocenter of source North - South (m) = monitoring seismometer

7 Background (4) Herein we present and discuss a procedure using azimuth of P-wave particle motion to constrain the initial source location. This procedure is demonstrated with a dataset acquired during fracture stimulation. Data from a single vertical array of sensors in a borehole, providing measures of arrival times and polarizations. Microseismic events are located using 1-D velocity models and arrival times of P- and S-wave.

8 Data -450 N 1100 Map View -500 Treatment Well Borehole Seismometer -550 North - South (m) Treatment Well Borehole Seismometer Depth (m) West - East (m) North South Cross Section North - South (m)

9 Processing Location procedure comprises following steps: Arrival times for 1,000 candidate events were manually picked. We estimated back-azimuth of the event by using polarization analysis of P wave. We added combination of polarities to remove 180 o ambiguity. We determined hypocenters location using guided grid-search optimization in the back-azimuth trace area to minimize all combinations of arrival times and sensors.

10 Arrival Time Picking (1) Ts Tp = s 0.05 s Sampling rate= s

11 Arrival Time Picking (2)

12 Arrival Time Picking (3) OT = s 24,21 24,205 24,2 24,195 24,19 24,185 24,18 24,175 24,17 24,165 24,16 [Ts - Tp] versus P Arrival Time y = 0,7873x + 24, ,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08

13 Back Azimuth (1) x = tan 1 A E A N N W Monitoring Station 270 O N 0 O 90 O South - North O Back Azimuth = o Event Sources Havskov & Ottemoller, West - East x 10 5

14 METER Back Azimuth (2) N Monitoring Station Event Sources METER

15 Polarization Analyses (1) window = s

16 Polarization Analyses (2) Amplitude Amplitude Amplitude Amplitude Time (s) 2 x Cut 104 Cut Waveform Waveform Amplitude Time Time (s) (s) 2 x Cut 104 Cut Waveform Waveform Cut Waveform Time (s) Time (s) 2 x 104 Cut Waveform Cut Waveform 5000 Amplitude Amplitude Cut Waveform window = s Time (s) Time (s) South - North South Down - North - Up South Down - North - - Up Down - Up - Up West - East Hodogram Hodogram West West - East East Hodogram Hodogram 1 Hodogram South 0 West - North 1 East West - East Hodogram Hodogram 1 0 Hodogram South North West - East Red = E-W Green = N-S Blue = U-D

17 180 o Ambiguity = tan 1 A E A N atau ? combination of polarities to remove 180 o ambiguity based on Havskov & Ottemoller, 2010

18 Remove 180 o Ambiguity (1) + Particle motion + + Calculated Back Azimuth is 39 o. But using combination, we must add 180 o so Back Azimuth is 219 o Havskov & Ottemoller, 2010

19 Remove 180 o Ambiguity (2) + Particle motion + - Calculated Back Azimuth is -48 o. But using combination, we must add 180 o so Back Azimuth is 132 o Havskov & Ottemoller, 2010

20 Guided Grid Search Optimization (1) N 1200 North - South (m) W N Calculate misfit for every grid. 600 Back Azimuth = 90 o West - East (m)

21 Guided Grid Search Optimization (2) Objective function for inversion Objective function in master station method T i t i t 0 C ri = Observed travel time = Observed arrival time = Origin time = Calculated travel time based on Zhou, 1994 Jones et al., 2013

22 Guided Grid Search Optimization (3) Calculated Travel Time (Shooting) vs Observed Arrival Time Depth (m) Depth (m) Observed Arrival Time (s) Resultant (m) OT = Calculated Travel Time (s) Resultant (m)

23 Discussion (1) N Map View North - South (m) Treatment Well Borehole Seismometer West - East (m)

24 Discussion (2) N Map View North - South (m) Treatment Well Borehole Seismometer West - East (m)

25 Conclude Remarks The processing of borehole microseismic needs more concern to remove ambiguity Inclusion of particle motion analysis can help to remove ambiguity and produce accurate solution of microseismic hypocenter The reliability of this procedure is supported by the results, where most of events cluster highlight coherent structures around treatment wells and inferred faults We hope that this procedure can be applied to various other cases such as microseismic monitoring in the field of CCS, CBM, geothermal, and shale-gas/oil exploration

26 REXHA VERDHORA RY Geophysical Engineering Institut Teknologi Bandung