Patent ID: 8693283

Claim:
A method of determining or detecting a change in a geophysical property of a subterranean region of the earth by determining time shifts Δt(t) between vintages of seismic data d(t) relating to a subsurface geological formation, the seismic data are acquired from the subterranean region, the method comprising: providing a number n of three or more vintages of seismic data d 1 (t), d 2 (t), . . . , d n (t) obtained from a corresponding number n of seismic surveys of the subsurface geological formation carried out at least a plurality of months or years apart, each vintage of seismic data d i (t) comprising at least one seismic trace, the seismic data being acquired using at least one seismic sensor in the seismic surveys; formulating an operator between a first number of the n(n−1)/2 possible amplitude differences Δd b,m (t) between pairs d b (t), d m (t) of the seismic data sets and a second number of the corresponding n(n−1)/2 possible time shifts Δt b,m (t), where the second number is arranged to be less than the first number by using a predetermined inter-relationship between at least some of the n(n−1)/2 possible time shifts Δt b,m (t), thereby forming an overdetermined set of equations solvable for the second number of n(n−1)/2 possible time shifts Δt b, m (t) using the operator and the first number of the n(n−1)/2 possible amplitude differences Δd b,m (t); and solving the overdetermined set of equations for the second number of time shifts Δt b,m (t) to determine the time shifts Δt(t); and determining the change in the geophysical property of the subterranean region of the earth using the determined time shifts Δt(t).