The ability of marine controlled-source electromagnetic (MCSEM) methods to
help image electrical conductivity contrasts below the Earth’s surface makes them useful
for both initial reconnaissance surveying for hydrocarbons and for delineating
prospective regions of high resistivity in development drilling.
A 3-D finite-element MCSEM Fortran algorithm used for forward modeling was
developed by Badea. Additional code was written and used for this thesis, with the goal
of enforcing more realistic electromagnetic (EM) Dirichlet boundary value conditions.
The results of the new boundary conditions on a MCSEM survey model, with a
hydrocarbon-saturated region in the subsurface, show that the method does not work as
hoped. Constant boundary values were applied to gauge the transmitter-receiver (TXRX)
range at which results are not boundary influenced, using a hydrate/hydrocarbon
model of the subsurface, at each of the three transmitter frequencies used in this study (1
Hz, 3 Hz, and 10 Hz). Results showed that electric field data were reliable to roughly
5000 m of TX-RX offset for the 1 Hz and 3 Hz cases, and to 6500 m offset for 10 Hz. The gas hydrate/hydrocarbon model was then run with zero-value boundary
conditions. The goal was to determine what effect changing parameters of the gas
hydrate, including hydrate radius, thickness, and depth, have on the EXEXS (xcomponent
of secondary electric field inline with the transmitter dipole axis) curves at
various offset, particularly in relation to a hydrocarbon-only model of the subsurface
response, so as to evaluate the EM masking effect the hydrate has on the hydrocarbon.
The results showed that the x-component of electric field in an inline survey is
dominated by the hydrate response, in all cases studied, with a couple of exceptions.
One exception is 1 Hz transmitter frequency at 2500 m to 3000 m offset when depth to
top of the massive gas hydrate zone was greater or equal to 250 m. Receivers at these
offsets would successfully detect the hydrocarbon target.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1932 |
| Date | 02 June 2009 |
| Creators | Dickins, David |
| Contributors | Everett, Mark E. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
Page generated in 0.0022 seconds