How is “a good mud tank” supposed to be like?

ultra short radius drilling

Currently I’m on duty in an oil well YYYYY. It’s a side track ultra short radius drilling (USRD) in Melandong area, Indramayu, West Java, Indonesia. Simply, it’s an extension of the old well but it plans to be drilled horizontally with short radius curve drilling which has the build rate around 1.5 – 3 °/ft? I guess so. . It needs special tools for sure that could spend a lot of money for it. USRD is use for special drilling purpose. Just heard about that, this kind of drilling is the first time which is being applied in that oil company. It’s really something new for me. But, actually this isn’t what here I want to explain about. It needs separated chapter.

Well, I’m a second mud engineer who now having ” a learning” with my senior. Firstly, I was so happy because I thought I’ll get a new knowledge about this, but then I shocked because everything here wasn’t established properly. I was doubt when I saw them in spite of their new appearance. The reality is extremely different. so, don’t be get fooled by the appearance of anything  Here, I suddenly become tank engineer and welding supervisor. I’ve been complaining all time coz most of the pit equipment and design aren’t supposed to belike that. Everyday, I ask to the welder to put some new tools, install it, modify and then test again. well, It is a lesson too, right? 🙂

All mistakes found in the rig

Well, let’s get detailed one by one:

Surface line/discharge

The design of surface line needs a lot of improvement. It has 4 active pit but only one that has discharge line from the hopper. I don’t know who has designed such pit. we couldn’t make much more mud though the space is actually available. It couldn’t transfer to other pit. So I can say that all pits they made are useless. sorry to say. Another vital mistakes founded is the window between active pit and the slug tank. It possibly contaminates each other. It needs to be closed / isolate permanently. Then, what we need to do is make a new dumped valve on the active pit. Every kind of pit need a dump valve and it isn’t supposed to be combined.

some mistakes

Standing valve

Standing valve is valve on the suction either to mud pump or hopper. They have 14 but none of them are in a good condition. It was leaking and we just know it be when there’s a mud pump test. We shocked since we saw the mud level in the pit was getting down gradually. the isolation of each tank is a MUST. We couldn’t know either kick or lost of circulation occurs. A good standing valve must be a choke. It easier settled down without getting any leaks or such things.

other mistakes

Shale Shaker

It’s first equipment that solid contaminated mud will be coming through. It handles 100% of circulating volume. It removes solids larger than 74 µm by straining it through the screen. It must have a high performance and in a good condition. Once it doesn’t, your mud system will be messed up. It’s hard to be cured unless it’s dumped and of course it costly (if we need to dump the mud all the time). All mud engineers know that the biggest contamination in a mud is solid. No other else. So, the role of all solid control equipment is urgent. What we need to do just to make sure this equipment is ok.

linear motion shale shaker

Here I found the weirdest shale shaker ever. It combined the typical derrick shaker and Brandt (Derrick and Brandt are two of well-know oilfield tool manufacturer). It uses a hard spring so its motion looks rigid. And the motor of the shale shaker is not balance; one motor has 2.5 HP, another 1.5 HP causing   motion become worst. My senior said that the Derrick’s shale shaker typically has a curve shape of the primary screen. It also has a scalper which be placed above it. The scalper has around 20 mesh in size. The Brandt’s shale shaker commonly has only one screen on it. It has pyramid shape and the surface is flat. What I found is the shale shaker is a modification between them i.e has a curve shape of primary screen but using flate screen on it. And it is getting worst by installing a rigid spring on it. The motor rotation direction is must be counter current, one vibrator must have a clockwise rotation and another counterclockwise.

Dump valve-sand trap

Dump valve is important when we plan to dump a contaminated mud or an excess on the system. It must be easy to be opened at once and doesn’t make any mess around the pit. Simply, everything that must be installed in the pit must have a safety consideration. A dumped valve in the sand trap must be a butterfly as it has a frequent time to dump the mud over there.

Gumbo Trap

A gumbo trap must be equipped with a channel to pass through the mud when it is getting full. Here I found that no channel on it, it could make a mess around there and of course it doesn’t safety.

Genset

There, the Genset was unstable which make our operation find some problem. Oh Please,,,make it in a good condition!

mud cleaner

Mud cleaner

Mud cleaner consist of desilter / desander mounted over fine mesh shale shaker. It uses in weighted and / or expensive fluid systems or to discards drilled solids while retaining expensive barite, chemicals and liquids in the fluid system. The hydrocyclone in desander is able to remove sand size (+74 micron) solids and desilter remove silt size (+20 micron) solids. When we had running test, to begin with, we have to adjust the pump suction opening for the roper piping and head pressure gauge as follow:

mud cleaner working principle

P opt = Pump suction head (~75 ft) x 0.052 x MW (ppg)

Or we can also use the rule of thumb:

P opt = 4 X MW (ppg)

Once the optimum pressure gauge achieve, the separation must be good. And the discharge of each cone must be an umbrella shape (cone not overloaded). A vibrator/motor for mud cleaner is less powerful compared to shale shaker. It commonly uses 1.5 HP each. When it runs on drilling activity, we need to check the nozzle on it (to make sure it isn’t plugged. Presence of vacuum at underflow indicates internal vortex and to assure the orifices are clear.

Agitator

Used on all active compartments to cool mud for return, keep mud blended for better sampling, suspend solids so that pumps and solids control equipment works more efficiently.

mud pit interior

The agitator must also be designed to make a flow regime on the pit become turbulent. So the impeller must be designed for that purpose. Axial mixing is a MUST. It minimizes the gradient of concentration in a whole mud system. When I had a field training there, my senior was arguing about the direction of it whether is begin from up to down. Well, when I see from Brandt presentation, it went up to down. But, I think it does the same. No much differences between them as long as it still an axial flow. So, does anybody could explain me which one is better? Oh, suddenly I remember my fluid mechanics lecture in college. He must know about it and could simulate it in CFD (computational fluids dynamics).

axial flow

Mud Guns

Mud gun is placed in every compartment for spot stirring only. The shearing action of nozzle causes solids degradation. It commonly used when there is sludge at bottom of tank due to settling of solid. We know it when the mud isn’t stirred but the mud weight is getting down.

Gas Separator

gas separator

In the mud world there is a term called gas cut mud. This is a soluble gas in the mud. It reduces mud weight, reduces hydrostatic head in well bore, causes centrifugal pumps to stop working and causes corrosion and scale problems. It also can accumulate in the hole and reduce the hydrostatic pressure gradually and possibly could make a kick.

When we found our mud has lower density due to the high gas content (based on mud logging unit) we need to pass the mud through separator. Mud and gas are diverted from the flow line and into the separator. Gas is released as the fluid impacts the baffles.  “Free” gas is collected at the top of the vessel and vented a safe distance for flaring or discharge to atmosphere. The drilling fluid returns to the active mud system where vacuum degassers remove additional entrained gas.

Degasser

Degasser

Vacuum degassers operate by separating gas-cut mud into thin layers followed by drawing off the gas with a vacuum pump.  The thin layers are achieved by flowing the mud over a series of baffles.