Seismic waves in rocks with fluids and fractures

Journal Article · Mon May 14 04:00:00 EDT 2007 · Geophysical Journal International

DOI:https://doi.org/10.1111/j.1365-246X.2007.03563.x· OSTI ID:928789

Berryman, J G

Seismic wave propagation through the earth is often stronglyaffected by the presence of fractures. When these fractures are filledwith fluids (oil, gas, water, CO2, etc.), the type and state of the fluid(liquid or gas) can make a large difference in the response of theseismic waves. This paper summarizes recent work on methods ofdeconstructing the effects of fractures, and any fluids within thesefractures, on seismic wave propagation as observed in reflection seismicdata. One method explored here is Thomsen's weak anisotropy approximationfor wave moveout (since fractures often induce elastic anisotropy due tononuniform crack-orientation statistics). Another method makes use ofsome very convenient fracture parameters introduced previously thatpermit a relatively simple deconstruction of the elastic and wavepropagation behavior in terms of a small number of fracture parameters(whenever this is appropriate, as is certainly the case for small crackdensities). Then, the quantitative effects of fluids on thesecrack-influence parameters are shown to be directly related to Skempton scoefficient B of undrained poroelasticity (where B typically ranges from0 to 1). In particular, the rigorous result obtained for the low crackdensity limit is that the crack-influence parameters are multiplied by afactor (1 ? B) for undrained systems. It is also shown how fractureanisotropy affects Rayleigh wave speed, and how measured Rayleigh wavespeeds can be used to infer shear wave speed of the fractured medium.Higher crack density results are also presented by incorporating recentsimulation data on such cracked systems.

• Research Organization: Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Basic EnergySciences
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 928789
• Report Number(s): LBNL--62925; BnR: KC0303010
• Journal Information: Geophysical Journal International, Journal Name: Geophysical Journal International Journal Issue: 2 Vol. 171; ISSN 0956-540X
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ANISOTROPY
APPROXIMATIONS
FRACTURES
RAYLEIGH WAVES
REFLECTION
SEISMIC WAVES
SHEAR
SIMULATION
STATISTICS
VELOCITY
WATER
WAVE PROPAGATION