Mapping hydrocarbon liquid properties of a kerogencontaining source rock

1. A method of hydrocarbon exploration within a subsurface kerogen-containing source rock comprising:

a. acquiring resistivity-hydrocarbon liquid property relationship-data of at least one of:

i. a set of samples of the source rock., the sample set spanning significantly different levels of maturity; and

ii. well-log data for a plurality of calibration locations within the source rock, the well-log data spanning significantly different levels of maturity;

b. measuring an electric or electromagnetic resistivity profile of the subsurface kerogen containing source rock using an electromagnetic profiling method, and

c. drilling for oil at a target location and/or depth, within the source rock, that is determined in accordance with:

i. the electric or electromagnetic resistivity profile of the subsurface kerogen containing source rock; and

ii. the resistivity-hydrocarbon liquid property relationship data of the set of source rock samples and/or well-log data.

2. The method of claim 1 wherein the hydrocarbon liquid property is selected from sulfur content, API gravity, and viscosity.

3. The method of claim 1 wherein the electrical or electromagnetic profiling method is a transient EM method.

4. The method of claim 3 wherein the transient EM method is long-offset transient electro magnetics (LOTEM).

5. The method of claim 1 wherein the acquired resistivity-hydrocarbon liquid property relationship-data is descriptive of the set of source rock samples.

6. The method of claim 1 wherein the acquired resistivity-hydrocarbon liquid property relationship-data is descriptive of the set of the well-log data.

7. The method of claim 1 wherein the acquired resistivity-hydrocarbon liquid property relationship-data is derived from maturity indicator measurements of samples of the sample set, the maturity measurement indicators being correlated with liquid property data.

8. The method of claim 7 where the maturity indicator is one or more of the following: Tmax, vitrinite reflectance, and Time-Temperature-Index (TTI).

9. The method of claim 7 wherein the acquired resistivity-hydrocarbon liquid property relationship-data is derived from artificially matured source rocks samples which comprise the source rock sample set.

10. The method of claim 7 wherein the well-log data includes NMR well-log data of hydrocarbon liquid viscosity at one or more subsurface locations within source rock, the resistivity-hydrocarbon liquid property relationship-data being derived from the NMR well-log data.

11. A method of hydrocarbon exploration within a subsurface kerogen-containing source rock comprising:

a. obtaining, from the subsurface kerogen-containing source rock, at least one of:

i. a set of samples of the source rock., the sample set spanning significantly different levels of maturity; and

ii. well-log data for a plurality of calibration locations within the source rock, the well-log data spanning significantly different levels of maturity;

b. acquiring resistivity-hydrocarbon liquid property relationship-data of the sample set and/or well-log data;

c. measuring an electric or electromagnetic resistivity profile of the subsurface kerogen containing source rock using an electromagnetic profiling method, and

d. drilling for oil at a target location and/or depth, within the source rock, that is determined in accordance with:

i. the electric or electromagnetic resistivity profile of the subsurface kerogen containing source rock; and

ii. the resistivity-hydrocarbon liquid property relationship data of the set of source rock samples and/or well-log data.

12. The method of claim 11 wherein the electrical or electromagnetic profiling method is a transient EM method.

13. A differential long-offset electromagnetic method of measuring one or more geological properties of a target sub-surface layer the method comprising:

a. in accordance with estimated upper and lower depths of the target sub-surface layer, respectively positioning first and second electromagnetic receivers at shorter and longer offsets from a dipole transmitter so that when the receivers receive an EM signal from the dipole transmitter after propagation through the earth:

i. the signal received by the first receiver at the shorter offset is governed primarily by a resistivity profile of the overburden above the upper depth of the sub-surface layer; and

ii. the signal received by the second receiver at longer offset is governed primarily by combination of the overburden resistivity profile and a resistivity profile of the target layer between the upper and lower depths;

b. sending an EM signal from the dipole transmitter into the earth so that the first and second receivers receive the EM signal after propagation through the earth;

c. synchronizing the EM signals from the first and second receivers;

d. computing a difference between the synchronized signals and

e. deriving the geological property from the computed difference.

14. The method of claim 13 wherein the receivers are positioned so as to be substantially co-linear with the dipole transmitter.

15. The method of claim 13 wherein the geological property is a thickness of the sub-surface layer.

16. The method of claim 13 wherein the geological property is a resistivity of the sub-surface layer.

17. The method of any of claims 13 wherein the geological property is a maturity of source-rock of the sub-surface layer.

18. The method of claim 13 wherein the geological property is an oil quality property of oil located within pore space of the sub-surface layer.

19. The method of claim 13 wherein the first and second receivers measure the electrical and magnetic fields in directions that are mutually orthogonal, and wherein the geological property is computed according to the results of the measurements in the mutually orthogonal directions.

20. The method of claim 13 wherein the synchronizing of the signals of the first and second receivers is carried out by employing a GPS signal and clocks in first and second receivers.