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W ELL CONTROL In workover and well-servicing situations, well control commands special considerations By Richard DeBuys, Wild Well Control utmost importance to minimize damage servicing operations as there are fields. Editor’s note: Mr DeBuys, under the auspices to the producing formations and still It may be as simple as a pump truck of the IADC Well Servicing Committee, pre- safely control the well. showing up and pumping a volume into pared this article detailing the substantial the tubing, or the crew just bleeding the The formation is the cash register. There differences in well control procedures and well down. But one thing is certain: The challenges between drilling and workover/ must be enough recoverable oil and gas best well control method is the pre-work well-servicing operations. to warrant financing workover and well- planning you put into it, then the execu- servicing operations, with a reserve to tion of that plan. Poor plan, poor well WHAT DO YOU call an operation properly abandon the well. Damage the control; good plan, good well control. that works with live hydrocarbon pro- formation, and your cash register con- ducing wells on a daily basis? If work- tains less, perhaps even ruining the well Many wells are still producing, decades over and well servicing sprang to mind, of economical recoverable reserves. after their initial completion, in an you’re right! While conventional drilling environment where not only the surface usually operates with a mud column conditions but also downhole conditions sufficient to hold formation pressures MUD VS CLEAR FLUIDS may be more hostile to equipment than in check to prevent an inflow of forma- Drilling operations are usually per- originally planned. The effect of down- tion fluids, workover and well-servicing formed with weighted fluids – mud – to hole harmonics, deterioration of met- personnel typically confront wells with prevent the well from flowing. A kick is als and the wear and tear on tubulars, exposed flow-capable hydrocarbon- avoided at all costs. Workover and well cement and surface equipment often bearing zones, and often begin their day servicing often use field water or clear require additional well control concerns. killing the well. brines. Both fluids have the same func- tion – to keep the well under control However, the majority of derrick-type This article will focus on fluids used and while work is being performed and to rig-based workover operations are con- other differences in operations, well con- minimize damage to formations. ducted in reservoirs where the driving trol and equipment between drilling and pressure has long been depleted. Pulling/ workover/well services. Mud consists of a liquid portion, usually water or oil, and solids, such as weight tripping operations are commonplace to I know the majority of the readers of this materials, clays and chemicals, to give it replace or repair downhole equipment. magazine are the drilling contractors. desired flow and carrying capacity. Both And it’s usually the routine operation On occasion, they are called to perform the solids and liquids may plug and dam- that has unanticipated well control prob- completions and even workover opera- age the formation. It is possible for the lems. tions. It has been said that drilling is liquid portion to filter into the formation Often, detecting a problem depends on easy; all you worry about are kicks, lost and swell native clays, whereas native different criteria than those used in drill- circulation and stuck pipe. Workover and field water may not. The solids may form ing (e.g., increase in flow, pit gain, etc ) . It well servicing have these problems and a wall cake, which may minimize the may be popping, pinging or other sounds many more, often unknown until you get mud’s liquid phase from entering the from the tubing or well, change in type into the well. formation and often allow heavier-weight or color of fluids from the well, smell fluids to minimize kick potential. The table on Page 103 contrasts com- or other signs and indicators that may plexities in workover/well servicing with There have been cases where an over- signify the onset of a well control event. those of balanced/overbalanced drilling balance of the drilling mud damages the Other areas may have ongoing forma- operations. These are generalizations, formation, and workover operations are tion injection processes, and if a well is do not include all problems and are not needed to acidize, stimulate or fracture opened prior to allowing the pressures to arranged in order of importance. the formation to get it to produce again. subside, a well control event may occur. THE DRIVING ECONOMICS A workover fluid, on the other hand, is This may be compounded by high- usually clear with few or no solids. It temperature (e.g., steam and fire flood During a producing well’s lifespan, it may enter the formation easily, even at injections) operations with equipment may go from primary hydrocarbon recov- the same weight as the original drilling and fluids hot enough to scald unwary or ery, i.e., an initial free-flowing well, to mud or less. Hydrocarbon and formation untrained personnel. one requiring secondary and tertiary depletion, loss of the formation’s drive recovery techniques, such as pumping mechanism, especially in areas that Th is discussion will be focused on der- and formation stimulation techniques. wells are fractured, all lead to problems rick-type rig-based workover operations Equipment may be added or changed between the formation’s pressure and where conventional well control methods out to try to squeeze as much as pos- the hydrostatic pressure of a fluid used (e.g., wait and weight, driller’s, con- sible from the formation. This may be a to keep the well from flowing prior to current, bullhead, etc ) aren’t typically well-orchestrated plan or reactionary, workover. utilized, such as pumping equipment, depending on what’s going on downhole, weight materials and mixing facilities sometimes both. CONTROLLING THE WELL may be nonexistent in the area or not readily available. Some of the techniques In workover and well-servicing opera- There are perhaps as many philosophies unique to workover include the “pill and tions, identifying the problem(s) is on how to keep the well static from flow- kill,” “rolling the hole” and “trickle” key. Regardless of what is done, it is of ing while performing workover and well- 102 March/April 2009 DRILLIN G CONTRACTOR W ELL CONTROL methods . Their use and effectiveness in WORKOVER AND COMPLICATION DRILLING controlling the well largely depend on WELL SERVICING the type of formation, type of fluids pro- Cementing DDduced, well pressures and experience in the area. Corroded/damaged tubulars D X The pill and kill technique usually uses Damaged casing D X field brine as the controlling fluid. A Daylight operations X sufficient quantity is pumped into the D well to keep it static, allowing workover Fish downhole D X operations to proceed. The brine may be pumped either down the tubing, casing Formation damage DDor both, usually the side the pressure Formation pressure and hydrocarbon depletion D X is on. The volume pumped usually is adequate to provide sufficient hydro- Fractured formations D X static pressure to prevent the well from Gas at surface D Not desirable flowing. Good mixing/pumping facilities X D Some formations may slowly accept the control liquid’s water and will begin High day rates X D to flow after a while. Still other areas Efforts made may use heavier brines to keep the well High potential for blowouts D static. In certain areas, concerns also to minimize exist regarding the stability of a fluid Efforts made left in the annulus. Over time, particles High potential for kicks D to minimize within a completion fluid, packer fluid or drilling muds may settle out or fall down Kick Detection Equipment X D to the top of the packer and can damage formations once the packer has been Kill fluid on location or ability to mix it Not always D released. It’s almost as much art as it is Logging DDscience, and personnel working in the field are experts on fluid type selection Lost circulation (LC) DDand how to keep the well static. LC mud and brines DDThe rolling the hole technique is used Multiple supervisory personnel X D to capture the oil inside the tubing. By pumping field brine into the annulus, the Oil at surface D Not desirable well will naturally “U-Tube” as the heavi- Operations start with killing well X er brine displaces a lighter oil up the D tubing. Once the brine reaches surface, Parted casing D X workover operations can begin. Pollution potential from oil/gas flow D X The above techniques may be inad- equate, especially when tripping out Potential for damaging formation DDof the well. The level of the controlling Pressure at surface D Not desirable liquid’s hydrostatic may drop due to the tubing’s displacement to a point where Pumps on location Not always D the well may begin to flow. Also, swab- Re-completing and perforating D X bing is a concern when pulling tight clearance equipment downhole, such as Re-establish production D X packers, and is also dependent on the Several trips per day X trip rate. Faster is not always quicker if D a well control event takes place. Stuck pipe DDWhen losses to the formations and/ Swabbing (intentional) D X or tripping displacement are concerns, some operations use a trickle method. Swabbing (unintentional) DDThis can be as simple as a hose con- Unweighted “clear” fluids DDnected to a nearby brine storage tank to operations involving pumps and pits Weighted drilling fluids D X with weighted brines.

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