Reservoir monitoring using galvanically excited transient electromagnetic fields
Methods, systems, and devices for characterizing an anomalous fluid body in an earth formation using measurements in a borehole intersecting the formation. Methods include galvanically exciting a transient electric field in the earth formation which interacts with an anomalous fluid body in the earth formation remote from the borehole; galvanically receiving a corresponding transient electromagnetic (TEM) signal; and using at least one processor to estimate a value of a parameter of the anomalous fluid body using the corresponding transient signal.
1. A method of characterizing an anomalous fluid body in an earth formation using measurements in a borehole intersecting the formation, the method comprising:
galvanically exciting a transient electric field in the earth formation which interacts with the anomalous fluid body in the earth formation remote from the borehole;
galvanically receiving a corresponding transient electromagnetic (TEM) signal; and
using at least one processor to estimate a value of a parameter of the anomalous fluid body using the corresponding TEM signal.
2. The method of claim 1 , comprising using an elongate conductor to perform galvanically exciting the electric field.
3. The method of claim 2 , comprising using a galvanic receiver to perform galvanically receiving the corresponding TEM signal, wherein the elongate conductor comprises installed casing, and the galvanic receiver is below the casing in the borehole.
4. The method of claim 1 , wherein the transient electric field generates time-dependent induced charges at an interface between the anomalous fluid body and the surrounding volume of the formation, and the corresponding TEM signal results from the time-dependent induced charges.
5. The method of claim 1 , comprising exciting the transient electric field at a first borehole depth and receiving the corresponding TEM signal at a second borehole depth substantially removed from the first borehole depth.
6. The method of claim 1 , further comprising estimating a change in the parameter over time.
7. The method of claim 6 , further comprising estimating fluid movement using the estimated change in the parameter.
8. The method of claim 1 , wherein the parameter comprises at least one of: i) a distance from an interface to a tool on which at least one of the transmitter and the receiver are disposed; and ii) at least one dimension of the anomalous fluid body.
9. The method of claim 1 , wherein the anomalous fluid body comprises a water-flooded zone resulting from injection of water to the earth formation through an injector well borehole intersecting the earth formation.
10. The method of claim 1 , further comprising creating a model of the formation using the estimated value of the parameter.
11. The method of claim 10 , further comprising conducting secondary recovery operations in dependence upon the model.
12. A system for characterizing an anomalous fluid body in an earth formation using measurements in a borehole intersecting the formation, the system comprising:
a transmitter configured to, when positioned in a borehore, galvanically excite a transient electric field in the earth formation which interacts with the anomalous fluid body in the earth formation remote from the borehole;
a receiver configured to, when positioned in the borehole below the transmitter, galvanically receive a corresponding transient electromagnetic (TEM) signal; and
at least one processor configured to estimate a value of a parameter of the anomalous fluid body using the corresponding TEM signal.