RE: :Origins of mud gas "Mud pressure was 600 psi in the first sidetrack, which would suggest an influx of reservoir gas boosting the mud gas readings.However, no gas kicks were reported".
The 600psi reading came from extrapolating final mud weight over well depth to show the 600psi increase. Influx still means a flow into the well, therefore no kick. There is nothing to show an influx of gas into the wellbore, only mud gas from drilling.
"In the second sidetrack over the same interval but extended another 250 ft deeper, much higher mud weights were used and , as expected, the mud gas readings were lower............presumably, these higher mud weights restrained the influx of reservoir gas"
With higher mud weights comes higher hydrostatic pressure PLUS added pressure to the formation from the resistance created from the dynamic forces of circulating drilling mud under pump pressure. The gas at the edges of the outside diameter of the wellbore would have been squeezed back into the formation from the added drilling fluid pressures created by heavier mud weight and thereby a reduction of drilled background gas
"If one were to standardize for the effect of mud weights ( ie remove its effect on mud gas due to the influx of rerservoir gas ) on mud gas readings, I would expect that the conclusion might be that of robust reservoir gas over portions of the 600 ft or so of the upper sands.
Strong reservoir gas cannot exist in tight sandstones, as most of the gas remains trapped within the low permeability rock".
There is that "I" word again. There was no INFLUX reported, only that word was used. An influx is the flowing of reservoir fluids/gasses into the wellbore while involved in a drilling operation.
The statement on reservoir gas and gas entrapment in low permeable rock is wrong. As long as there is permeability there will be flow. If the formation is tight then fracing can be used to enhance flow.
There was no influx or kick, well flow reported, but there were significant mud weight increases, With the new mud weights reported then we still have to assume that these upper sands are still considered to be overpressured.
"But, I am not an expert"
Not many are considered to be experts but it is becoming apparent that you are not in a learning frame of mind either. I don't post to blow smoke and I only write about what I know to be true. I feel good to help folks understand the operational side of some of the pieces of well drilling so if they are interested, then I am hopeful that what I write is clear to readers and can be absorbed.
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