Method and apparatus for real time oil based mud contamination monitoring

1. A method of determining oil based mud contamination of a hydrocarbon fluid obtained from a wellbore during formation testing, the method comprising:

receiving a reservoir model for simulating the contamination using a microprocessor;

receiving an empirical equation for computing the contamination using the microprocessor wherein the empirical equation for computing the contamination comprises

Fitted_Optical

⁢

_Density

=

C

-

D

×

t

-

5

12

wherein t equals time, C and D are solved by using a parameter estimation method to fit acquired data and the percent of contamination is computed by:

Contamination

=

100

×

C

-

Fitted_Optical

⁢

_Density

C

;

for a first pumping time, separately generating a simulated contamination based on the reservoir model and an empirically computed contamination based on the empirical equation contamination using the microprocessor;

comparing the simulated contamination and the empirically computed contamination using the microprocessor;

selecting one of the reservoir model and the empirical equation as more accurate and another one as less accurate for the first pumping time using the computer; and

revising the less accurate one of the reservoir model and the empirical equation based on a result of the comparing.

2. The method according to claim 1 , further comprising:

revising the less accurate one of the reservoir models based on a result of the selecting; and

for a second pumping time, repeating the generating, comparing, selecting and revising operations.

3. The method according to claim 1 , wherein in the case the empirical equation is selected as the less accurate one of the reservoir models, revising at least one of: a fitting parameter, or a power of the first pumping time.

4. The method according to claim 1 , wherein the simulated contamination generating includes:

building a history-matching model based on the reservoir model; and

implementing history-matching using the history-matching model.

5. The method according to claim 1 , wherein the reservoir model is a semi-analytical simulator.

6. The method according to claim 1 , wherein in a case that the simulated contamination and the empirically computed contamination are sufficiently consistent according to a preset threshold, further comprising determining whether the contaminations are sufficiently small such that the hydrocarbon fluid qualifies as a representative fluid sample for the formation testing.

7. The method according to claim 1 , wherein the generating, comparing, selecting and revising operations are implemented in substantially real time with the formation testing.

8. The method according to claim 4 , wherein the comparing is iterated until the simulated contamination obtained from the history-matching model matches the empirically computed contamination to a preset extent.

9. The method according to claim 1 wherein receiving the reservoir model for simulating the contamination comprises:

(a) receiving input data characterizing a reservoir;

(b) producing the reservoir model in response to said input data representing said reservoir in multi dimensions;

(c)verifying the reservoir model; and

(d) using said reservoir model, generating the simulated contamination in said reservoir in response to the verifying step.

10. The method according to claim 9 wherein the producing includes the steps of:

(b1) calculating the oil based mud contamination of a hydrocarbon fluid obtained from a wellbore in one dimension associated with a single layer in said reservoir, the oil based mud contamination existing at a single point in space in said reservoir and at a single point in time in said reservoir,

(b2) calculating the oil based mud contamination in said one dimension associated with multiple layers in said reservoir, the oil based mud contamination in each of said multiple layers existing at a single point in space in said reservoir and at a single point in time in said reservoir,

(b3) calculating the oil based mud contamination in three dimensions associated with said multiple layers in said reservoir, the oil based mud contamination in each of said multiple layers in said three dimensions existing at a single point in space in said reservoir and at a single point in time in said reservoir,

(b4) calculating the oil based mud contamination in said three dimensions, said values being associated with said multiple layers in said reservoir, the oil based mud contamination in each of said multiple layers in said three dimensions existing at a single point in space in said reservoir, the oil based mud contamination in said each of said multiple layers in said three dimensions existing at any future point in time in said reservoir.

11. A non-transitory computer readable medium having a computer program product stored thereon for determining oil based mud contamination of a hydrocarbon fluid obtained from a wellbore during formation testing that when executed on a computer comprises:

receiving a reservoir model for simulating the contamination;

receiving an empirical equation for computing the contamination wherein the empirical equation for computing the contamination comprises

Fitted_Optical

⁢

_Density

=

C

-

D

×

t

-

5

12

wherein t equals time, C and D are solved by using a parameter estimation method to fit acquired data and the percent of contamination is computed by:

Contamination

=

100

×

C

-

Fitted_Optical

⁢

_Density

C

;

for a first pumping time, separately generating a simulated contamination based on the reservoir model and an empirically computed contamination based on the empirical equation;

comparing the simulated contamination and the empirically computed contamination;

selecting one of the reservoir model and the empirical equation as more accurate and another one as less accurate for the first pumping time; and

revising the less accurate one of the reservoir model and the empirical equation based on a result of the comparing.

12. The non-transitory computer readable medium according to claim 11 , further comprising:

revising the less accurate one of the reservoir models based on a result of the selecting; and

for a second pumping time, repeating the generating, comparing, selecting and determining operations.

13. The non-transitory computer readable medium according to claim 11 , wherein in the case the empirical equation is selected as the less accurate one of the reservoir models, revising at least one of: a fitting parameter, or a power of the first pumping time.

14. The non-transitory computer readable medium according to claim 11 , wherein the simulated contamination generating includes:

building a history-matching model based on the reservoir model; and

implementing history-matching using the history-matching model.

15. The non-transitory computer readable medium according to claim 11 , wherein the reservoir model is a semi-analytical simulator.

16. An apparatus comprising:

a) a system for implementing a reservoir model for simulating the contamination;

b) a system for implementing an empirical equation for computing the contamination, for a first pumping time, separately generating a simulated contamination based on the reservoir model and an empirically computed contamination based on the empirical equation wherein the empirical equation for computing the contamination comprises

Fitted_Optical

⁢

_Density

=

C

-

D

×

t

5

12

wherein t equals time, C and D are solved by using a parameter estimation method to fit acquired data and the percent of contamination is computed by:

Contamination

=

100

×

C

-

Fitted_Optical

⁢

_Density

C

;

c) a system for comparing the simulated contamination and the empirically computed contamination;

d) a system for selecting one of the reservoir model and the empirical equation as more accurate and another one as less accurate for the first pumping time;

e) a system for revising the less accurate one of the reservoir model and the empirical equation based on a result of the comparing until the simulated contamination and the empirically computed contamination are within a preset limit; and

f) a system determining whether the simulated contamination and the empirically computed contamination are sufficiently small such that the hydrocarbon fluid qualifies as a representative fluid sample for the formation testing, and if not implementing the system for selecting for a second pumping time.

17. The apparatus according to claim 16 , wherein the system for generating simulating contamination includes:

building a history-matching model based on the reservoir model; and

implementing history-matching using the history-matching model.

18. The apparatus according to claim 16 , wherein the reservoir model is a semi-analytical simulator.