Downhole measurement of formation characteristics while drilling

1. A method, comprising:

directing a mixture comprising first formation fluid and drilling mud from a wellbore annulus into a mud gas logging tool;

acquiring mud gas logging data by analyzing the mixture to determine first fluid type estimations;

directing second formation fluid through a sidewall of the wellbore and into a sampling tool;

acquiring second data associated with a sidewall fluid sample measurement by analyzing the second formation fluid;

comparing the mud gas logging data to the second data associated with the sidewall fluid sample measurement to determine whether the first fluid type estimations are as expected; and

adjusting calibration data associated with the mud gas logging tool in response to determining that the first fluid type estimations are not as expected.

2. The method of claim 1 further comprising performing the comparison of the mud gas logging data to the second data in response to determining that the mud gas logging data indicates a change in a fluid composition.

3. The method of claim 1 wherein the second data is one of a fluid composition or a concentration of a fluid component.

4. The method of claim 1 , wherein analyzing comprises measuring a composition of gases separated from the mixture.

5. The method of claim 1 , wherein the sampling tool is coupled to the mud gas logging tool as part of a bottom hole assembly.

6. The method of claim 1 , wherein analyzing the second formation fluid comprises performing optical spectrometer measurements.

7. The method of claim 1 , wherein directing second formation fluid comprises extending a probe from the sidewall of the sampling tool to engage a wall of the wellbore.

8. A method, comprising:

directing a first mixture from an annulus of a wellbore into a mud gas logging tool;

acquiring first mud gas logging data by analyzing the first mixture to determine first fluid type estimations;

generating predicted fluid type estimations using the acquired first mud gas logging data;

directing a second mixture from the annulus into a mud gas logging tool;

acquiring second mud gas logging data by analyzing the second mixture to determine second fluid type estimations;

determining whether the second fluid type estimations correspond to the predicted fluid type estimations; and

initiating a sidewall fluid sample measurement through a sidewall of the wellbore in response to determining that the second fluid type estimations do not correspond to the predicted fluid type estimations.

9. The method of claim 8 further comprising acquiring second data associated with the sidewall fluid sample measurement.

10. The method of claim 9 further comprising:

comparing the second mud gas logging data to the second data associated with the sidewall fluid sample measurement; and

adjusting calibration data associated with a mud gas logging tool based on the comparison of the second mud gas logging data and the second data associated with the sidewall fluid sample measurement.

11. The method of claim 8 , wherein the predicted fluid type estimations comprise a predetermined fluid composition.

12. The method of claim 8 , wherein the predicted fluid type estimations comprise a predetermined concentration of a fluid component.

13. The method of claim 8 , wherein initiating a sidewall fluid sample measurement comprises directing formation fluid into a sidewall of a downhole tool.

14. The method of claim 8 , wherein initiating a sidewall fluid sample measurement comprises extending a probe from a sidewall of a downhole tool to engage a formation and directing fluid from the formation into the downhole tool through the probe.

15. An system, comprising:

a mud gas logging tool configured to acquire mud gas logging data and comprising a first sensor operatively coupled to a tool inlet for admitting fluid contained in a well;

a sidewall fluid sampling tool operatively coupled to the mud gas logging tool and comprising a second sensor configured to selectively couple to a formation penetrated by the well to acquire sidewall fluid sample measurements;

a controller configured to determine first fluid type estimations based on the acquired mud gas logging data, to employ the acquired sidewall fluid sample measurements to determine whether the first fluid type estimations correspond to expected fluid type estimations, and to adjust calibration data associated with the mud gas logging tool in response to determining that the first fluid type estimations do not correspond to the expected fluid type estimations.

16. The apparatus of claim 15 further comprising a directional drilling assembly configured to adjust a well trajectory based on at least one of mud gas logging data and sidewall fluid sample measurements.

17. The apparatus of claim 15 further comprising a probe configured to form a fluid communication with the formation penetrated by the well.