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Drilling Fluid:
Methods to Regain
Circulation The only sure method for curing loss circulation is to set casing, this can't all way be done for one reason or another, so other method have to be considered. Other measures can frequently be successful. The first step to be taken when total loss of circulation occurs is to attempt to fill the annuals while making sure the drill string is in a safe zone. Then critically examine the operating practices and the mud properties at the time the loss was noted. Correct any deficiencies. Sometimes the waiting period and the needed modifications are sufficient to restore circulation. If, however, the hole still cannot be filled with water, determine the level at which the water stands. Treatments to regain circulation usually are applied batch wise. "Soft plugs" do not require long periods of waiting, as does cement, nor do they cause undesirable changes in the properties of the mud used in drilling. Bridging and plugging agents, should be mixed with bentonite-water mud to a consistency as thick as can be poured or pumped into the hole. Under normally conditions, the most cost-effective method for preventing fluid loss to the formation is to add lost circulation materials (LCMs) to the drilling fluid. LCMs consist of scrap materials, such as cottonseed hulls, crushed walnut shells, ground coal, ground battery casings, wood chips, expanded clay, and ground rubber that act as bridging materials or filtrate control materials that form pressure-tight seals across the lost-zone fractures or formation pores. A mixture of sizes and types of lost-circulation materials usually is more effective than a single, un-graded material. Do not continue to pump away successive large volumes of mud of the same composition. Drilling blind (i.e., pumping enough drilling fluid to cool the bit and lift the cuttings into the zone of loss) in some instances is the least expensive procedure. Before pumping any slurry pull the bit to a safe area, The mix need to be big enough to do the job and it is wise to give yourself 300 or 400 feet of plug out side and under the bit, By allowing the mix to gravitate and settle in without force you stand a better chance of building a base on which to build. A mixed LCM pill, using a concentration of 20-30 lb/bbl. is allowed to penetrate fractures/voids and let sit for a while before attempting to circulate if you can circulate you can applying squeeze pressure (200-500 psi). if it does not hole or you are pushing the LCM into the formation the procedure may have to be repeated until the formation will hold One of the major problems with total lose return is have you got past it. I have always found that if you stop where you first lose the problem is still there when you clean out. Depending on the well condition Well control wise is whether I continue to drill until the formation hardens up.
Then cure the loss. This can be done by lining one pump on the annuals
to keep the hole full and drill with the other pump letting the cutting go
into the loss zone "Drilling Blind"
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