Detection of Mobile Fluids Kandiah Balachandran Pacific Coast Section - SEG, September 9, 2015

The Main Points Common receiver gathers are “always” more coherent than common shot gathers (field records) Cause: Scattering close to receivers is more important than those close to the source Anomalous event on horizontal component seismograms suggests the possibility of direct detection Scattering is analogous to “coupling”, impedance matching, etc. and involves conversion from P to S

Anomalous Event: P- to SV- wave Conversion at Near Normal Incidence May Be An Indicator Of Mobile Fluids Fractures and heterogeneities may be associated with guided waves – the strength and persistence may help in estimating properties of reservoirs especially in marine surveys (large offsets).

Typical good record Refractions Ground Roll Reflections Multiples P-S converted reflections

Typical NG Record Refraction ??? Scattered noise Elastic Scattering converts P- waves to S- waves partially

Hammer Blow Experiment Powder River Basin X X … X O O O … O R1 … R24 S1 S2 S3 S8 R1 – R 24: 6 in. (15 cm) spacing S1 – S8: 12 ft (3.66 m) spacing S – R offset: 6 in. to 96 ft (29.3 m)

Common Receiver Gathers from Hammer Blow Experiment

VSP – Eastern Saudi Arabia Elevation view Plan View Shots up the hole nearest four seismometers 590 ft to 10 ft at 10ft 10 ft from hole

Reversed VSP Signals recorded at one surface seismometer for shots at depths ranging from 590 feet to 10 feet at 10-foot intervals

Another reversed VSP

Comparison of signals from the deepest 4 shots at the four surface seismometers surrounding the Borehole

Mounds Test Site

Velocity Profile-Amoco Ennis

Field Layout – Sapulpa, OK

Normal Wave Tests

Transposed Wave Test Each panel is a collection of signals recorded at one particular receiver station from weight drops at the 2-ft spaced source locations

CONCLUSIONS P- to SV- wave Conversion at Near Normal Incidence may be an Indicator of MOBILE FLUIDS FRACTURES other heterogeneties may be the cause of guided waves

Selected References Balachandran, K., Horizontal Component Seismograms: SPE preprint 7437, 1978 Balachandran, K., Seismic problems in clinker areas, http://classes.kvcc.edu/kbalachandran/, 1972 Balachandran, K., Noninterchangeability of sources and receivers, Geophysics, 39,73-80, 1974 Frankel, A., and Clayton, R.W., 1986, Finite difference simulations of seismic scattering, JGR, 91, 6465 - 89 Hudson,J.A., The Attenuation of surface waves by scattering: Proc. Camb. Phil. Soc., 67, 221-32,1970

References (continued) Levander, A.R. and Hill, N.R., 1985, P – SV resonances in irregular low-velocity surface layers, Bull. Seis. Soc. Am., 75, 847 – 64 Can we use dynamic elastic nonlinearity measurements of rocks to map reservoir properties? Tawassul Khan, Sofia McGuire, OGJ Sept.10, 2001 In situ seismic shockwaves, Sergei Kostrov, William Wooden, Peter Roberts: OGJ Sept.3, 2001