For example, ....................approximately 5,530 and 5,920 feet TVD with difficulty maintaining adequate mud weight from 5,631 feet DUE TO THE INFLUX OF GAS. This section drilled was interbedded SANDSTONE AND SHALE with an INFERRED GAS COLUMN based on the mud log data of approximately 390 feet."
There is a lot to be said about a carefully worded news release. "Influx" of gas means that the formation flowed into the wellbore. That simply means that there was a kick from overpressure but no kick was reported, only words to show that mud weight was increased due to "influx of gas". The word influx is confusing as it indicates a flow from the formation that is drilled and into the wellbore and apparently, that has not been the case. Read my long post from the 27th, the paragraph about background gas and that should give you a better understanding of drilled gas/mud gas/ background gas.
"Its my understanding that a strong gas influx can only occur in a permeable and porous section.
If the gas is tight, most of it will remain trapped in the rock and a strong gas influx would not be expected."
Gas "influx" can come from ANY formation if gas is there and if the mud column is not heavy enough to overcome formation pressure. If it's the sandstone that you are thinking of then influx can occur if the formation characteristics show it to be tight or highly permeable. It is not so much a factor in either case if the mud column pressure is underbalanced. Influx represents a kick and this was not reported.
"And Also...........Lost circulation was encountered at 6,173 feet TVD resulting in the decision to stop drilling and log the well. The wellsite cuttings description indicated the lithology of the formation being drilled when losses occurred to be sandstone, and VERY HIGH MUD GAS READINGS WERE OBSERVED OVER THIS INTERVAL.
In other words, the section in which lost circualtion occurred ( at about 6173 ft ) also had very high mud gas readings. Recall that this section was much more porous and permeable, as the drill rate tripled from 16 ft/hr to 54 ft/hr."
This first paragraph shows that the sandstone was HIGHLY porous and very permeable to accept whole volumes of drilling mud as the mud was more overbalanced to overcome the highly permeable sandstone section and it's formation pressure. I will say that if this hole section had the same characteristics as the section of the drilling break, there would be a very high risk of the string being stuck again. Also, note that it shows *mud gas readings and not influx. Is that a correction for the use of the word "influx"? Mud losses were recorded at 6173' but it does not correlate to the drilling break that went from 16'/hr to 54'/hr. That occured at 5920'.
"I view such information as positive, but have no certainty about how this could be quantified relative to commecial indicators."
The gas has been identified as to be the same as the neighboring field, methane, and for the thickness of the sands I would guess that this well will be a high producer. The only question I have would be to formation damage due to excessive mud weights if that is actually the case, and then the addition of cement to the highly permeable sand zone. Perhaps the action of perforating of the well will overcome any formation damage that MAY have occured when they get to that stage.
"That they were still in strong gas saturation lithology when they lost circulation is also encouraging, as is this second attempt to fully penetrate to TD and their stated view that even if this attempt fails, they will come back later and redrill again."
Why is loss circulation encouraging? I think NOT.
There should be no thoughts of a redrill. There are no indications showing that a loss of the well is imminent or a possibility, however, to case off these upper sands as hole size is now reduced could be prudent. A well with the new well program could then be made to visit Parigi if it turns out to not be a possibility on this well
*We are without facts. An influx means a kick, in essence, and no kick was reported so that choice of word may cause confusion. You have to understand drilled gas/ background gas. As my previous post tried to explain, these mud gasses cannot necessarily be controlled although a situation could arise from mud gasses becoming high enough through poor drilling practices where gas cut mud could effectively reduce hydrostatic pressure where an influx could occur. Mud gas in a well where mud weight is adequate to control formation pressures is ONLY the gas that is liberated from the formation rock that is drilled out of it's natural state as it has laid for millions of years. From it's solid state and with gas within it's pores, the drill bit generates tiny chips from the formation as the hole is drilled and the mud weight has this gas in compression as it is driled. As the mud circulation carries the chips or drilled cuttings to surface and towards atmospheric pressures, it comes up the hole and to the degree that the mud weight's hydrostatic pressure is reduced by the height of the mud column as the chip is pumped to surface with the mud circulation, the gas expands from the loss of hydrostatic pressure so it is liberated from the rock pores and expands to be released into the drilling mud as drilled gas. Meanwhile, under these same conditions, drilling may continue with full integrity of the well and with the drilling mud weight hydrostatic pressure safely containing the formation pressure.
As for this particular well and with facts at hand, I believe that a sequence of events occured to have this well too overbalanced in terms of current mud weights as reported. I feel that a mud weight can be established to control the well but yet not have it too heavy to flow into highly permeable sands as loss circulation. It's possible that these well problems are a form of self inflicted woulds, so to speak.
Also, lower permeability sets up conditions to allow for differential sticking of the drill string with differential pressures between drilling mud hydrostatic pressures and formation pressures being too high where high permeability rock has characteristics where differential sticking conditions don't come into play.
Without going into a well control lesson, higher pressures can be more problematic at shallower depths than with deeper wells. I consider this to be a shallow well.
I'm sure the company has a good understanding of the formations and pressures associated with both target zones. In my case from a lack of understanding of the same idea, I worry about formation pressure differentials between these problematic upper sands and Parigi.
I hope this offers some clarification. .....any questions?