Patent Document ID: 20090005994
Application ID: 12280509
Patent Flag: 0

Claim One:
1. A method for determining time-dependent changes in the hydrocarbon content of a subsurface reservoir from controlled-source electromagnetic survey data obtained from the subsurface region containing the reservoir, said method comprising: (a) obtaining electromagnetic field data recorded at a plurality of online and offline (relative to a survey source line) receiver locations from an initial survey of the subsurface region, and corresponding survey results from at least one later survey of the same region conducted under substantially the same conditions, said data comprising a field component sensitive at least predominantly to vertical resistivity and a field component sensitive at least predominantly to horizontal resistivity; (b) for each survey, solving Maxwell's electromagnetic field equations for horizontal resistivity and vertical resistivity at a plurality of (x, y, z) positions in the subsurface reservoir, using survey acquisition parameters and the measured electromagnetic field data; and (c) comparing calculated resistivity results between the surveys.