RE:RE:RE:RE:For CGX drilling teamHi Dirk,
Thanks for your comments regarding cementing through BHA. I understand that what you haven't done before may look like "insanity" to you but it is actually something that is done every now and then. No offencce, we all have several things we have never done in our careers, the job is just too diverse.
Here below I send come extracts from Spread on the subject, you're certainly familiar with it, right? There is also an SPE paper.
GLTA,
I am wondering what experience and comments the good folk of the community have in the following scenarios;
1) Max concentrations of LCM with just a mud motor (PDM) in the string.
2) Pumping a cement plug in bad lost circulation zones through (a) just a motor and (b) a BHA including a motor and MWD tool.
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I have had no problems pumping 80-100 ppb LCM pills, Thermatek and cement thru Pathfinders HDS-1L MWD. It is a simple probe style tool and very, very robust.
Unlike other tools there´s no need to dip the pumps when pills and potions pass thru, you can just keep on trucking. Also the tool surveys over a phenomenal flowrate range, so you will always have MWD even at 1/3 or less of your maximum flowrate. I have seen one that was re-runable even after three Thermatek pills and 6800 ton of barite had been thru it. The Pathfinder motors are the best in my opinion and again no problems with LCM or cement. As with all directional companies, they have ”˜LCM limits´, but needs must when the devil drives.
Circ subs can help, but you have to find a good, multi shot one. PBL subs are OK, but I would be willing to try another manufacturers sub. I would prefer to cement thru the bit rather than thru a circ sub and down the outside of the BHA.
I think that most the plugging problems pumping LCM at high concentrations or cement are a mix of poor fluid properties and poor drilling practices. I have even seen folk trying to ”˜pump & pull´ with LCM pills - too subtle a trick I think.
Here´s my take on good practices:
LCM Pill Preparation
Space out string to put bit or PBL sub above suspected loss zone. Also space out for BOP.
Be prepared for plugged suction/discharge screens on mud pumps. Remove screens if necessary before pumping LCM. Have relevant permits and tools in place for removing suction/discharge strainers etc.
Pump LCM with one pump only to prevent having both pumps blocked with LCM.
Pump LCM on the run, if possible.
Depending on LCM concentration/recipe pumped, dress shakers accordingly
Do not leave unpumpable volumes of LCM in bottom of the pill pit. Add fresh mud to get the LCM moving with the agitator.
Spotting Pills thru Bit
Do not stop pump until LCM pill is fully displaced thru bit
Overdisplace LCM by 5-10 bbls
Calculate top of LCM pill
POOH slowly until bit above top of LCM pill. Space out for BOP.
Rotate string at 20-30 rpm and break circulation - look out for blockages in the string. Stage up pumps and monitor loss rate. Establish maximum loss free circulating rate.
Wash back to bottom & drill ahead.
Spotting Pills thru PBL Sub
Do not stop pumps until LCM pill is fully displaced thru PBL Sub
Overdisplace LCM by 3- 5 bbls
Calculate top of LCM pill and mud volume below LCM pill/PBL Sub
POOH slowly until bit above top of LCM pill - trip will be wet, the vinyl ball is on seat in the PBL Sub. Space out for BOP.
Rotate string at 20-30 rpm and break circulation - look out for blockages in the string. Stage up pumps and monitor loss rate. Establish maximum loss free circulating rate.
Drop steel ball to clear ball seat of vinyl ball - confirm full circulation with correct flowrates & SPP through bit/BHA.
Wash back to bottom & drill ahead (if only it was that easy!)
Pumping cement would follow pretty similar lines, but you will have to WOC. You should get all the spacers and cement into your drillpipe so that you can displace without having to shut the pumps down. If you have a mixed DP string, then try and get all the flushes/spacer/cement in the larger DP before you displace. That way you can concentrate on your SPP and strokes to see what is going on.
If you think the cement is going to work, you might want to displace with water (you´ll need a float in the string to trip/strip out). That way you can ”˜see´ more surface pressure on your SPP gauge to tell you what is happening. A ”˜cheat sheet´ will help if you plan to squeeze some away.
Sometimes folk talk about the additional shearing that the cement sees when passing thru the bit nozzles and the possibility of flash setting. As far as I know, there is only one standard test involving shearing that all cement pilot tests get regardless of where in the well it goes or how it gets there. If you are concerned about the extra shearing thru the nozzles, slow the pumps when the cement passes thru.
Downhole circulating and static temp data from your MWD can help with your cement/thermatek pilot testing.
If you know there´s going to be losses, then make sure that the motor and MWD can still work at reduced flowrates. That´s the beauty of a rotary assembly, you can get any flowrate/RPM/WOB combination you want. People generally set up the MWD so that it operates near the low end of range when at drilling flowrates. I prefer to do it the other way and have the drilling flowrate at the top of the tools range, so that as you cut the pumps back, the tools will still work. An MWD that operates over a very large range (without requiring an orifice or choke) has benefits here.
If you are in an area with known severe problems,then you should really be looking at what tools are reliable and then pick the directional contractor that way.
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SPE Paper 128734-MS is a case history for large volume cement squeezes...some through the BHA/Motor...
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Most of our drilling procedures for drilling in vugular carbonatres include the use of close tolerance rotor/stator PDM's as well as a full component of MWD/LWD tools. We have routinely pumped in excess of 150 ppg LCM and cement through these BHA's. They key is no fibrous materials, the pills and slurries have been effectively sheared, and the PDM's have been relined with quality elastomers.
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When attempting to cure seepage losses through a mud motor using a blend of calcium carbonates in fine and medium size grades is good. Also better when combined with fine and medium grades of fibre type materials to enable blending and meshing of the materials in the fluid. This helps produce a webbing effect when trying to seal off micro fractures for example in the formation.
For dealing with severe downhole losses when you have a downhole motor included in the BHA it depends on the severity of the losses. If you have enough mud avaliable and can keep the hole full you can then POOH to lay down the motor and any measuring tools. This then enables you to RIH with a simple bit assembly without nozzles and you can then pump a volume of thixotropic cement to help seal off the loss zone fairly quickly and have enough time to pull the pipe out so BHA is well above the cement plug. This requires careful planning which needs to be done by the drilling team and the cement company together.
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Major operator has routinely pumped 8 to 14 lb/sk Diaseal M (or equivalent high fluid loss pill) in cement for severe to total losses through motor only and motor+MWD. Practice has been done for nearly ten yrs. Slow pump rate as LCM Cement pill passes through BHA. Small tools pose higher risk as noted in one of the other comments.
Halliburton Gulf of Mexico staff have procedures, recipes.
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Max LCM through MWD tools Baker , Schlumberger & Halliburton states 40 PPB, I have pumped up to 80 as long as there is no coarse material.
the best solution is to install a pump out sub in the BHA then you can go up to 120 PPB all sizes and types of LCM.
no problem to pump cement through MWD of bits for LCM.