ARHT Media Inc V.ART.H

RE: RE: RE: RE: A short note about testing.

[GreatSwami]

In order to understand the time likely taken for testing it is important to understand what they actually do on a test and the mechanics of the whole process.

The first thing a test is designed to do is to prove or disprove that there is some permeability in the formations that have been drilled. Wireline logging operations will have either proven or disproven the presence of any porosity and quantified both its location as well as its magnitude. (The open hole log data can be processed to gain an inferred permeability - but this is a little indirect). The drilling itself will also no doubt have confirmed permeability from ongoing mud losses or fluid volume gains - or "kicks!"

The test does this by opening up the reservoir zone being tested to atmospheric pressure (modified by the hydrostatic head from a "water cushion" in the drill pipe perhaps? A water cushion is simply a column of water placed in the testing string pipe exerting greater than atmospheric pressure on the downstrream side of the test valve so that the pressure differential is reduced making potentially huge flows easier to control during initial valve open periods). Typically with fracture porosity there is huge permeability - although this can be reduced significantly by drilling solids plugging (and lost circulation material). Considering that at the reservoir depth of 3,558-3908m - normal reservoir pressures could be in the range of 34-36 Mega Pascals (thats a lot of pressure - about 4,800 psi - one atmosphere is approximately 0.11 Mega Pascals!).

The second thing that a test does is to recover and flow any fluids that are resident in the reservoir - both native and introduced - and fluids will be produced unless the zones being tested are absolutely dense and tight with no porosity or permeability. (Some matrix porosity in certain very special reservoirs can be completely sealed off by drilling fluid damage effects - but these cases are quite rare and are usually related to low pressure dessicated low to very low permeabilty zones).

When you run a test the testing cycle goes through several stages. The test tool is run in on drill pipe, the sealing packers are inflated and "set," the test valve is opened for a pre flow period. If no water cushion is present that 4,800 psi zone in the reservoir is suddenly open to 14-15 psi atmospheric pressure (plus the weight of the 3500m of air column above the test valve). Trust me - if there is any permeability at all - fluids will flow from that high pressure zone towards that low pressure opening! Typically the pre-flow is designed to last from 5-15 minutes and is simply a way to flush out any mud and drill solids plugging the pore throats. After that short valve open pre-flow the well testing valve is shut in and pressure build up in the sealed interval measured. Even if the pre-flow is not enough to uncork all the plugged pores allowing an obscene ingress of formation fluids (drilling mud, water, oil and/or gas) the pressure in the interval will have dropped on valve open and will rise back up again as soon as the valve is closed. The nature of that pressure rise tells an experienced tester evrything they need to know about the reservoir permeability - EVEN IF NO FLUIDS ARE PRODUCED! (The build up will appear almost instantaneous = excellent permeabilty; show a very steep rise followed by a rounded shoulder = moderate permeabilty; or show a much more gradual rise = low permeability; and even an erratically stepped profile = a horrendously damaged plumbing system. There are type charts for all the various possibilities of reservoir type and damage scenarios).

Following this initial shut in - which can be an hour or two hours - a second flow is started lasting anything from 90 minutes to 2 hours before the valve is shut in again. During this second flow stage fluids can enter the drill pipe and flow to surface where they can be collected, separated and measured. (Gas, oil and water). When the well is shut in the second time the valve shut time can extend from 2-3 hours (or longer?) and the shape of this pressure build up is compared to the shape of the build up after the preflow period. Typically they show a very similar profile and rise to the same end reservoir interval pressure. (Any amount by which the second shut in pressure is less than the initial shut in pressure can be interpreted to show potential reservoir depletion caused by removal of the amount of fluid flowed during the intervening valve open period.) For any huge reservoir there will be no measurable depletion.

The remainder of the test can be extended or terminated as desired. If there is a need to test the extent of a large reservoir then a very extended test is performed on a third valve open period which can extend for days or week as they remove a sizeably significant fluid volume before performing a final shut in pressure build up - a final shut in who's duration is typically double that of the preceeding flow period. The only testing time constraints relate to surface handling capability and the safty considering the nature of the fluids produced. (Really sour oil and gas zones introduce safety and corrosion hazards - and are not normally extended too long on initial testing programs).

Lets sum this up.

If there is no permeability - there is no reason to extend the testing. One you will know from the logs and testing itself very quickly if there is no permeabilty. (You will also know very quickly if there is good permeability but that it has been badly damaged).

If there is excellent permeabilty - once all the plugging drill mud and drill solids have been expelled the native reservoir fluids will show up - be they gas oil or water. If it is water - you do not need to flow it very long to determine if it is mud filtrate or native reservoir water. Similarly if it is gas - there is a need for some reasonable test times to get pressure data and test gas samples to determine if there could be a downdip oil leg to the reservoir. If it is oil - it doesn't take long to determine what it is and what its character is. But it does take an extended flow to determine any near well boundary conditions or to eliminate the possibility of the reserve being a small local accumulation.

The behaviour and reservoir engineering evaluation of both the flow periods and the shut in period pressure build up behaviour will determine most of the knowable reservoir parameters - and these forms of data are quite robust.

As to whether they would risk the ability to safely drill ahead by perforating the behind pipe pay zones of the upper Shiranish or Aaliji - even though they can do a cement squeeze to seal them off - I really do not think anyone would do this on such a well. The potential short term reward does not even begin to justify the potential (and very real) risks of jeopardising the risks involved. Far better to test the open hole section, get flow rates and useful data, then drill deeper if there are compelling reasons to do so, then (and only then) test the new hole followed by a staged testing of each other potential zone moving up the hole from deepest to shallowest. Waiting a few more weeks or a month for such results pales into insignificance against losing the ability to drill deeper from being both impatient and imprudent - if that is required or desired...

While it is concievably possible that they have simply had a bear of a time getting a proper test - I would have expected a news release if this was the case. (I fully expect that could quite easily have encountered a misrun or two on testing - that sort of thing is commonplace - but it only takes up a few days of rig time per misrun at most.)

There are some rumours that I may have been optimistic in how much of the Cretaceous they have opened up with this well - I do not have access to any well logs so I really cannot say. All we know for sure is that they are at least some 540-550m below the top of the Shiranish - so wherever that takes them is where they are? If they are not in any lower Cretaceous zones - then they could simply have an extremely thick Shiranish - but if that is so having 500m+ of oil filled fracture porosity cannot be construed as being a bad thing - right?!

GS