Friday, August 13, 2010

Well there's yer problem right there

 I remember reading about how during drilling the original well, there was a point they got the drill head stuck, and actually had to sever the drill string and drilling head, leave it in the hole , back up, cement the hole, and re-drill in a different angle.

What would cause this...?

I remember reading about lost mud during the original drilling operation too.....

I stumbled on what is called " underbalanced drilling "

    " Underbalanced drilling, or UBD, is a procedure used to drill oil and gas wells where the pressure in the wellbore is kept lower than the fluid pressure in the formation being drilled. "

 "  Underbalanced drilling is usually more expensive than conventional drilling, and has safety issues of its own. This is true when combustible and corrosive gasses like processed flue gas and oxygen are injected into the drilling mud to lower its density. Drilling underbalanced may be pointless from a formation damage standpoint if the underbalanced condition can not be maintained - which can be difficult when the drillstring needs to be removed to change a bit, or if the flow must stop in order to allow mud pulse telemetry to be sent. Information is frequently needed from the bottom of the well (knowledge of bottom hole pressure is very important in underbalanced drilling, as is information for geosteering if it is a deviated well). When gas is injected into drilling mud, standard mud pulse telemetry becomes impossible. "Killing" the well (making it overbalanced) may be necessary to send information, inducing formation damage. Underbalanced drilling also increases the chances of the wellbore collapsing in on itself. "

 ....something I noticed from the analysis of the oil.....1800ppms of nitrogen....

   " If the formation pressure is relatively high, using a lower density mud will reduce the well bore pressure below the pore pressure of the formation. More commonly, inert gas is injected into the drilling mud to reduce its equivalent density and hence its hydrostatic force throughout the well depth. This gas is commonly nitrogen, as it is non-combustible and readily available, but air, reduced oxygen air, processed flue gas and natural gas have all been used in this fashion.   "

"  The problem of differential sticking is eliminated. Differential sticking is when the drill pipe is pressed against the wellbore wall so that part of its circumference will see only reservoir pressure, while the rest will continue to be pushed by wellbore pressure. As a result the pipe becomes stuck to the wall, and can require thousands of pounds of force to remove, which may prove impossible. Because the reservoir pressure is greater than the wellbore pressure in UBD, the pipe is pushed away from the walls, eliminating differential sticking. "

"   Differential sticking is a problem that occurs when drilling a well with a greater well bore pressure than formation pressure, as is usually the case. The drill pipe is pressed against the wellbore wall so that part of its circumference will see only reservoir pressure, while the rest will continue to be pushed by wellbore pressure. As a result the pipe becomes stuck to the wall, and can require millions of pounds of force to remove, which may prove impossible. In many cases the drilling fluid (mud) weight is simply reduced, thus relieving the pressure difference and releasing the stuck pipe string. "

 From Wikipedia, on wellbore stability and drilling muds.

  • Chemical composition and mud properties must combine to provide a stable wellbore. Weight of the mud must be within the necessary range to balance the mechanical forces.
  • Wellbore instability = sloughing formations, which can cause tight hole conditions, bridges and fill on trips (same symptoms indicate hole cleaning problems).
  • Wellbore stability = hole maintains size and cylindrical shape.
  • If the hole is enlarged, it becomes weak and difficult to stabilize, resulting in problems such as low annular velocities, poor hole cleaning, solids loading and poor formation evaluation
  • In sand and sandstones formations, hole enlargement can be accomplished by mechanical actions (hydraulic forces & nozzles velocities). Formation damage is reduced by conservative hydraulics system. A good quality filter cake containing bentonite is known to limit bore hole enlargement.
  • In shales, mud weight is usually sufficient to balance formation stress, as these wells are usually stable. With water base mud, chemical differences can cause interactions between mud & shale that lead to softening of the native rock. Highly fractured, dry, brittle shales can be extremely unstable (leading to mechanical problems).
  • Various chemical inhibitors can control mud / shale interactions (calcium, potassium, salt, polymers, asphalt, glycols and oil – best for water sensitive formations)
  • Oil (and synthetic oil) based drilling fluids are used to drill most water sensitive Shales in areas with difficult drilling conditions.
  • To add inhibition, emulsified brine phase (calcium chloride) drilling fluids are used to reduce water activity and creates osmotic forces to prevent adsorption of water by Shales.

 Now, I will admit,...I have been having trouble with idea of this being close to " over ".....I didn't after they initially got the " 3-ram capping stack " installed, in fact I was tickled.  But I immediately began to have doubts because of flip-flopping from Thad Allen , Ken Wells and all the other high-level persons involved in this .

 .......all of a sudden this is not appearing to be a cut-n-dry situation

 .......I think about the amount of sand/particulates in the crude....

.........where did it come from......? large a void has been created by letting this well run for almost 3 months....?

........perhaps one of the most bothersome things, for me, is the continued venting of gases from the sea-floor.

.......The hydrate stability zone only extends 1000' down.

.......Hydrates normally form in the mudline/stability zone because of contact with liquid and temperature/pressure ( P/T )

......let's say that a flow of crude has found it's way from a lower level leak around the wellbore.

.....let's also say that it has eroded a pathway through the solid lithofied layers of rock, all the way up to the mudline.

.....the oil would cool down, the contraction of the cooling oil , and the reduction in pressure from vertical migration would allow gases to sublimate from the fluid.

.....normally, this gas would start to form hydrates as soon as P/T and seawater allowed it.( as it migrated upwards through the silt/mud )

.....however, ...we have all been watching various gases venting from the seafloor for almost 4 weeks now. the mud/silt...there's water for the hydrates to form...

......there's gas necessary to form hydrates........

......the pressure is conducive to hydrate formations.....

......what's missing from the equation here.....?

......Temperature's cool enough to allow hydrates to form...that's what's missing.

......not only temperature,....but over-saturation of gases in the mudline.

......since any leaking oil migrating through alternate channels would be rising against ambient pressure in the seafloor, it would be rising slowly. my question after all that conjecture is :

Is crude oil building in a massive deposit under the mudline....?

Basically pooling under the mudline....?

I do not for one second think that only gases would be leaking form this well at any point of damage in the bore.

It is a physical impossibility ?

This video does not share characteristics of any natural methane seep footage I have watched, that is why I am starting to question whether these "seeps" are natural, skip to 1:50 if you want to see what I am curious about.


Drilling Fluids said...

Drilling fluids are of three types of viz. Oil Based Fluids (OBFs), Water Based Fluids (WBFs) and Synthetic Based Fluids (SBFs). These fluids are used for drilling of natural gas, oils and water wells.

Isaacnd said...

And what category would you put the emulsions in ?