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Drilling Fluid: Methods to Regain/restore CirculationThe only sure method for curing loss circulation is to set casing, this can't all waybe 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 fillthe annuals while making sure the drill string is in a safe zone. Then criticallyexamine the operating practices and the mud properties at the time the loss wasnoted.

Correct any deficiencies. Sometimes the waiting period and the neededmodifications are sufficient to restore circulation. If, however, the hole stillcannot be filled with water, determine the level at which the water stands.

Treatments to regain circulation usually are applied batch wise. "Soft plugs" donot require long periods of waiting, as does cement, nor do they cause

undesirable changes in the properties of the mud used in drilling. Bridging andplugging agents, should be mixed with bentonite-water mud to a consistency asthick as can be poured or pumped into the hole.

Under normally conditions, the most cost-effective method for preventing fluidloss to the formation is to add lost circulation materials (LCMs) to the drilling

fluid. LCMs consist of scrap materials, such as cottonseed hulls, crushed walnutshells, ground coal, ground battery casings, wood chips, expanded clay, andground rubber that act as bridging materials or filtrate control materials thatform pressure-tight seals across the lost-zone fractures or formation pores.

A mixture of sizes and types of lost-circulation materials usually is more effectivethan a single, un-graded material. Do not continue to pump away successivelarge volumes of mud of the same composition. Drilling blind (i.e., pumpingenough drilling fluid to cool the bit and lift the cuttings into the zone of loss) insome instances is the least expensive procedure.

Before pumping any slurry pull the bit to a safe area, The mix need to be bigenough to do the job and it is wise to give yourself 300 or 400 feet of plug outside and under the bit, By allowing the mix to gravitate and settle in withoutforce 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 cancirculate you can applying squeeze pressure (200-500 psi). if it does not hole oryou are pushing the LCM into the formation the procedure may have to berepeated 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 whenyou clean out. Depending on the well condition Well control wise is whether Icontinue to drill until the formation hardens up.

Then cure the loss. This can be done by lining one pump on the annuals to keepthe hole full and drill with the other pump letting the cutting go into the loss zone

"Drilling Blind"

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A rapidly filtering, high-solids slurry often is effective in sealing vugular andfractured formations by forming a bridging mass of particles. Diatomaceousearth, or diatomaceous earth and asbestos, is mixed in the proportions of onepound of solids per gallon of water and placed in the zone of loss. Fine fracturesare bridged by the cake formed