Docstoc

Passive seismic analysis for reservoir monitoring - QUEST ITN

Document Sample
Passive seismic analysis for reservoir monitoring - QUEST ITN Powered By Docstoc
					           Passive seismic analysis for reservoir
                        monitoring

                            September 24, 2010


                       Capo Caccia, Sardinia, Italy



D. Gei, L. Eisner, P. Suhadolc
Outline

•   Hydraulic stimulation of reservoirs
•   Passive seismic monitoring
•   Surface star array data: some examples
•   Focal mechanism inversion of microseismic events
•   P-wave traveltime inversion for VTI media
Hydraulic stimulation of reservoirs
Hydraulic stimulation is a technique to induce fractures in hydrocarbon and
geothermal reservoirs.

• It is injection of fluids under high pressure in order to overcome minimum stress
  and open a hydraulic fractures, either by opening existing fractures or producing
  new ones.
• It increases the permeability of the rock from microdarcy to millidarcy range.
• The fluid injected into the formation is typically composed of brine (95%),
  additives, proppant (e.g. resin-coated sand, ceramic materials).
• The stimulated volume can extend several hundred meters around the well. The
  dimensions, extent, and geometry of the induced fractures are controlled by
  pump rate, pressure, and viscosity of the fracturing fluid.
• Reservoir hydraulic stimulations usually induce (significant) microseismic
  activity.
Perforation shots
Perforation shots serve to connect wellbore and formation through opening in casing




                   Heel                                                                   Toe




                                                Stage 2                     Stage 1
    Low permeability,                                                                        Perforation shots
    hydrocarbon-rich formation
      (picture after API Guidance Document HF1, Hydraulic Fracturing Operations – Well Construction and Integrity Guidelines,
      First Edition, October 2009)
Hydraulic stimulation
                         Fluid injection




                                               Stage 2                     Stage 1
                                                                                             Microseismic events
    (picture after API Guidance Document HF1, Hydraulic Fracturing Operations – Well Construction and Integrity Guidelines, Fisrt Edition,
    October 2009)
Passive seismic for reservoir monitoring
Passive seismic monitoring of reservoirs consists in “listening” to the
subsoil during oilfield operations (e.g. production, hydraulic stimulation,
CO2 injection).
    Location of events and clustering
      Map fracture system
      Cap rock integrity
      Fault mapping (reservoir compartmentalization)

    Focal mechanisms
    Anisotropy analysis (P and S waves)

    Fracture characterization
       Fracture orientation
       Fracture density and aspect ratio
       Microseismic signals can be recorded by downhole sensors or
       surface star arrays of receivers.


Monitoring well            Treatment well
                  ~300 m




                                                             Depth (kft)
                                                                                                                   Microseisms

                                                                                            Treatment wells


                                                                           Northing (kft)
                                    (from Warpinski, 2009)
                                                                                                   Easting (kft)

 Vertical array of 3C geophones (8-12 receivers)                                 Hundreds of receivers disposed in a
 in a monitoring well.                                                           star shaped array
Hmax




                     Treatment well
                     (deviated)




        (picture from www.microseismic.com)
Data example




               Microseismic event 1

               Perforation shot
Microseismic event 1


Lines 1 - 10

Processing performed

Bandpass freq filter
(2,7,60,70) Hz
Agc for visualization
 Microseismic event 1


Lines 1 - 10

Processing performed

Bandpass freq filter
(2,7,60,70) Hz
                        Polarity flip   Polarity flip
Agc for visualization




                                                        Polarity flip   Polarity flip
Microseismic event 1: frequency analysis of the seismic signals
              Data from line 10 (1C)
              Raw data




    Time window width: 0.032 s




                                                                                         Line 10
                                                                  Line 10
      Polarity flip  source location




                             Red line: frequency peak of the spectrum for each seismic trace
Perforation shot
Perforation shot

                                                                     Well head   Receivers
          Direct arrivals from the perforation shot




                                                                                 Perforation shot


                                   Direct waves from the well head
Surface waves from the well head
Focal mechanisms
Focal mechanisms: event 1




                                                              OK




                    Focal mechanism: oblique dip-slip fault
Focal mechanisms: event 6




                    Focal mechanism: strike slip fault
Vertical Transverse Isotropy (polar anisotropy)
Anisotropic material: properties (e.g. seismic velocities) depend on
direction. Vertical transverse isotropy can be related to fine layering in
sedimentary basins or to shales.




                           5 independent elasticity constants (c11, c33, c44, c66, c13)

                   Thomsen parameters (weak anisotropy)
P-wave traveltime inversion for homogeneous
VTI media




                                                                                      , , VP0
             picked arrival time

             origin time                            Experimental traveltimes
                                                *
                                                •   Computed traveltimes (t0=-0.005 =0.1 =-0.1 )
             one-way vertical traveltime        •   Computed traveltimes (t0=0.007 =0.2 =0.3 )
                                                •   Computed traveltimes (t0=0 =0.1 =0.22 )
             P-wave velocity // symmetry axis

             offset (horizontal projection of

             source-receiver distance)

                normal moveout velocity

            Anellipticity (Alkhalifah and
            Tsvankin, 1995)
P-wave traveltime inversion of   P-wave velocity profile
perforation shot data




   Perforation shot
P-wave traveltime inversion of perforation shot data

Traveltimes from                                  Traveltimes from synthetic
experimental data                                 data (ray tracing - isotropic
(layered anisotropic ?                            layered medium)
medium)




                         Effective velocity for
                         traveltime inversion
      ,                                                  , 
P-wave traveltime inversion from experimental data

  Picked arrival times

                                                      Experimental data
                                                      Inversion results: vti




                         Time (s)
                                                      t0 = -0.244 s
                                                       = 0.2734,   0.1172
                                                      RMS  4.0 ms




                                                     Experimental and theoretical
  Time residuals                                     traveltimes - Line 1
P-wave traveltime inversion from synthetic data

  Picked arrival times

                                    Synthetic data
                                    Inversion results: VTI




                         Time (s)
                                    t0 = -0.001 s
                                     = 0.1217,   0.0148
                                    RMS  1.1 ms




                                                             Synthetic and theoretical
  Time residuals                                             traveltimes - Line 1
P-wave traveltime inversion from synthetic data

  Picked arrival times

                                    Synthetic data            Experimental data
                                    Inversion results: VTI    Inversion results: VTI




                         Time (s)
                                    t0 = -0.001 s             t0 = -0.244 s
                                     = 0.1217,   0.0148     = 0.2734,   0.1172
                                    RMS  1.1 ms              RMS  4.0 ms




                                                             Synthetic and theoretical
  Time residuals                                             traveltimes - Line 1
Conclusions

 This dataset is characterized by non-unique focal mechanism

 The reservoir and/or the overburden are affected by polar anisotropy
  Bibliography

Alkhalifah, T., and I. Tsvankin, 1995, Velocity analysis for transversely isotropic media: Geophysics, 60,
1550-1566.
API Guidance Document HF1, Hydraulic Fracturing Operations – Well Construction and Integrity
Guidelines, First Edition, October 2009 (http://www.gwpc.org/e-
library/documents/general/APi%20Hydraulic%20Fracturing%20Guidance%20Document.pdf)
Fischer, T., Hainzl, S., Eisner, L., Shapiro, S.A. and Le Calvez, J., 2008a, Microseismic signatures of
hydraulic fracture growth in sediment formations: observations and modeling. Jour. Geoph. Res., 113,
B02307, doi:10.1029/2007JB005070.
Grechka, V., 2009, Applications of seismic anisotropy in the oil and gas industry, EAGE Publications bv.
Jupe, A.J., Jones, R.H., Wilson, S.A., and Cowles, J.F., 2003, Microseismic monitoring of
geomechanical reservoir processes and fracture-dominated fluid flow, Fracture and In-Situ Stress
Characterization of Hydrocarbon Reservoirs, Geological Society, London, Special Publications.2003,
Ameed, M.S. (Ed); 209: 77-86.
Maver, K.G., Boivineau, A.S., Rinck, U., Barzaghi, L., and Ferulano, F., Real time and continuous
reservoir monitoring using microseismicity recorded in a live well, First Break, 27, 57-61.
Thomsen, L., 1986, Weak elastic anisotropy, Geophysics, 51, 1954–1966.
Warpinski, N., 2009, Microseismic Monitoring: inside and out, JPT, November 2009, 80-85.
Acknowledgments

  We are grateful to Microseismic Inc. for supporting and providing us
  with the dataset. We thank Vladimir Grechka for providing us with the
  P-wave traveltime inversion code.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:4
posted:10/28/2011
language:Italian
pages:27
xiaohuicaicai xiaohuicaicai
About