directional drilling 2

[ahmedchn]

Directional drilling?
hi.i have a very big confusion in directional drilling. my question is if i have to drill a trajectory like build hold and drop so suppose i have drilled the the build and hold section . now i am making my bottom hole assembly to drill the drop section.so my BHA has to drill the drop section but it passes from the build and hold section so how it can drill ?

 

[DrillerNic]

Three options:

drill each section with a dedicated dumb iron BHA: a build assembly, a hold assembly and a drop assemblt. The difference in each is basically the stabiliser arrangement: RIH with a drop assembly through the build and the hold sections shouldn't be a problem... the BHA will want to take teh easy route going downhole rather than kick off a new hole. Just be careful RIH! Downside of this is that it's lot of trips and rig time, you can't really control the well trajectory (other than by tweaking your drilling parmeters).

Drill with an adjustable gauge stabiliser, so a hold BHA can be converted to a drop BHA without a round trip. You still have the problems of controllability, but you can do more than adjust the WOB...

Drill with a steerable assembly of some kind- either a bent motor or a full rotary steerable system. Both will happily drill the build, hold and drop sections in one go, are highly controlable (ie if you drop slightly on the hold, you can nudge the trajectory back). Rotary steerable systems are often faster (pipe rotates all teh time) and deliver a cleaner hole (pipe rotates all the time) and smoother hole (pipe steers all the time, so loweer totuosity as no steer/ straight, steer / straight you get from a motor). But they are more exapensive

 

[ahmedchn]

thank you for your answer. i have a one very basic question also and that is while drilling the directional well using dedicated dumb iron BHA so does the hole drilling string (from rotary table to bit) rotates in every section like (build,hold and drop) ? please tell me that what type of BHA rotates and what not ?

 

[shawnpeter]

a dumb iron BHA = everything from the bit, collars, etc will be in rotation.

 

[ahmedchn]

but how it can be possible that every thing rotates especially when we are in inlination?can u give any example ?plz plz plz help me !!!!!

 

[shawnpeter]

well, scratch that... in our case we called it "dumb iron" when the bha was a locked assembly, rotary/top driven. you could have the same bha in addition to a mud motor.

what I/we call dumb iron may be different from other definitions.

 

[DrillerNic]

What I call a dumb iron assembly is just that- lumps of steel. You rely on different stabiliser arrangements to produce different fulcrum effects to either lift the drill bit or drop the drill bit, or in the packed hole, hold assembly, to eliminate any fulcrum effects to drill straight ahead. Everything rotates, but you have to remember that while drill pipe looks quite string and rigid, in the scale of a drill string thousands of feet long and 5" across, it resembles a human hair and is quite flexible (if you've ever dropped a stand of drill pipe in the derrick you'll know exactly how flexible drill pipe is!). So the normal build rate is 3° per 100ft- ie a circle with a circumference of 12,000ft.

When steering with a bent motor, the size of the bend in the motor is usually about 0.6° (more than that and the motor wears out and the directional drilling company gets upset), and you drill in two modes: sliding and rotating. When sliding, the bend is oriented the direction you want to steer, the mud motor only turns the bit and the rest of the drill pipe is stationary and you shove the drill string along, for say 15 feet. You then rotate everything for 20ft and drill a straight section of hole, before orientating again and slide drilling another 15ft, repeating the process until you have achieved the turn you want.

A rotary steerable system rotates everything all the time with the steering being done automatically by a tool just behind the bit, either pushing the bit sideways in the direction you want to go or pointing the bit in the direction you want to go. The different service companies either have 'point-the-bit' or 'push-the-bit' systems and will spend a lot of time telling why their point the bit philosophy is better than the other guy's push the bit idea....

Generally steering with dumb iron is almost unheard of now, and I doubt if there's many people alive who can still do it and reliably get where you want to go. Steering with a motor is a bit of an art, and you have to know what the DD is doing (check his slide sheets to make sure he's not being lazy and giving you a 3°/ 100ft hole with high dog legs- ie all the steer in 20ft, then rotate for 80ft while he has a coffee in the DD shack!). Rotary steerable systems give you lovely smooth holes, and keeping the hole clean is much easier as the pipe rotates all the tiome, which is a big problem when sliding, especailly in high angle holes. You can have teh trajectory pre porgrammed in and off it goes- you can even hook teh rotary steering head up with the logging tools and it will steer automatically for you! But they are very, very very, expensive. And most DD's I know don't really like them, as they don't get to go up to the drill floor and tell the driller what to do every 20 ft... "I just stay here in the shack watching the computer- all the fun's gone out of it!" is a comment I've heard a lot.

 

[docellen]

I've heard that the relief well has to hit the casing in the old well precisely centered and at 90 degrees, or they won't be able to drill thru the casing. Does that mean their turning rate will be much faster than 3 degrees per 100 feet?

I've heard also that they are going to send high-frequency pulses down the old well casing to serve as a guidance signal for the driller. How far away can they pick up that signal? What are the chances of hitting center the first time?

 

[DrillerNic]

docellen- they know where the target well is with pretty good certainly- they have a definitve survey- so the turn rate won't be a problem.

The one time I've done an intersect well, we used magnetic ranging, which was good for about 3- 400ft. It took us several attempts to hit the well (but we'd previously milled out too much of the target well's casing by accident, so the accuracy was lower. Also teh direction drilling company weren't necessarily the best available...)

Electronic ranging might have a longer range; I don't know. I'm not sure how they would get the high frequency electrical pulses down the well: a long cable from surface and an ROV?

 

[docellen]

I would expect the bottom of the casing to act as a very good upside-down antenna. The problem might be in driving the top of the casing with enough power to get past the conductive layers, which will short the antenna to ground. Maybe it will take a megawatt transmitter at the top to get a few watts at the bottom, but then it should be quite easy to get a direction on the signal through a few hundred feet of rock.

All this is just my guessing as an electrical engineer. I have no experience with the actual equipment.

 

[waross]

There is portable equipment for locating pipes and cables on the surface. It will probably take more power on a subsea casing but probably not in the megawatt nor even the high kilowatt range.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[docellen]

All depends on how much conductivity there is in the water-filled layers above where you want to detect the signal. Let's assume we have 1000 feet of mud and rock saturated with seawater, and we need to get a 1 milliwatt RF signal through that layer. The optimum frequency will probably be what makes the "antenna" below the conductive layer resonate, let's say 100kHz. How much attenuation do we get in that 1000 feet? If it's 90dB, you will need a megawatt at the top to get a milliwatt at the bottom.

Could the conductive layer be more than 1000 feet? I see from the casing diagram that they used seawater for drilling the first 2891 feet, then switched to oil-based mud. The seawater left around the outside of the casing could provide a pretty good shunt to ground.

 

[DrillerNic]

docellen- what they are trying to pick up is proabably the magnetic field interference due to the target well's casing (ie a disturbance in the regional earth's magnetic field ) ... I can't see how they can get an electric signal down the target well: a 5000ft cable, an ROV and a big jubilee clip?

 

[ahmedchn08pg]

hi.i would like to ask from all drilling professionals that is there any particular type of drilling fluid recommended by API in a particular formation? if i have to drill sandstone,limestone,dolomite so there are different drilling fluid used in them ? could you please name drilling fluid in a particular formation type ?

 

[DrillerNic]

There are two main considerations in drilling fluid design: the rehology (ie the physical characterisitcs) and the chemistry.

Rehology: you want a fluid that is viscous enough to carry drill cuttings, but not so visocus that you can't pump it. You also want a fluid that will lock up or gel when you stop pumping to hold the cuttings in suspension. These things push you towards a no-newtonian fluid: a shear thinning fluid like tomato ketcup or HP sauce. Drilling fluids do this by adding polymers: clays like bentonite or natural polymers like guar gum or xanthan gum or a whole host of acronyms: CMC, HEC, PAC, PHPA.

In terms of chemistry the big problem is hydrating clays: clays absorb water to become mud; it's what clays do. Some clays absorb water really easily and quickly, and if these reactive clays are in the drilled formations, the wellbore will start to collapse and you lose BHAs and all sorts of bads things. The easiest way to avoid this problem is to remove the water: drill with an oil based mud. But OBM has environmental and safety implications. So start drilling with what is called an inhibitive fluid, a fluid that inhibits the absorbtion of water by clays.

The simplest (and cheapest) inhibitive fluid is a calcium mud (or gyp mud which uses gypusm to supply the calciumm). The Ca++ ion blocks the water molecules from getting to the reactive clays. As the reactivity of the clays increases, you move to Potassium Chloride, and the K+ ions does teh same thing. This is why one of the important parts of a mud reports is the salinity and the Ca++ or K+ content: how inhibitive is the fluid? The "KCL-polymer" mud has become the standard water based mud in the industry: KCL brine plus a couple of polymers such as PHPA and PAC, bentonite, a pH modifyer such as soda ash and perhaps a weighting agent.

The next step up in inhibitive water based muds are the silicate muds. They are expensive, and I've never used them as OBM has always been a cheaper alternative on my wells (even with cuttings disposal factored in).

The other chemistry problem is drilling salt: WBM dissolves salts and you get big washouts. So remove the water by using OBM, or stop dissolution by using salt saturated mud.

The main thing to check is what you are drilling through: salts, reactive shales (check the CEC- cation exchange capacity- to see if you have reactive clays).

In terms of drilling sandstone, dolomite and limestone you shouldn't have any problems from chemistry: a gyp mud or KCL mud should be OK. Speak to the mud companies and ask them to recommend something!

 

[amyamster]

if you are looking for information on directional drilling, check out

http://www.directionaltech.com.

It has extensive explanations on installing water, sewer, gas, fiber and other applications of using this technique.