MUD LOGGING

Directional drilling1. n. [Drilling] ID: 1341

The intentional deviation of a wellbore from the path it wouldnaturally take. This is accomplished through the use of whipstocks,bottomhole assembly (BHA) configurations, instruments tomeasure the path of the wellbore in three-dimensional space, datalinks to communicate measurements taken downhole to the surface,mud motors and special BHA components and drill bits. Thedirectional driller also exploits drilling parameters such as weighton bit and rotary speed to deflect the bit away from the axis of theexisting wellbore. In some cases, such as drilling steeply dippingformations or unpredictable deviation in conventional drillingoperations, directional-drilling techniques may be employed toensure that the hole is drilled vertically. While many techniquescan accomplish this, the general concept is simple: point the bit inthe direction that one wants to drill. The most common way isthrough the use of a bend near the bit in a downhole steerable mudmotor. The bend points the bit in a direction different from the axisof the wellbore when the entire drillstring is not rotating. Bypumping mud through the mud motor, the bit turns while thedrillstring does not rotate, allowing the bit to drill in the direction itpoints. When a particular wellbore direction is achieved, thatdirection may be maintained by rotating the entire drillstring(including the bent section) so that the bit does not drill in a singledirection off the wellbore axis, but instead sweeps around and itsnet direction coincides with the existing wellbore. Rotary steerabletools allow steering while rotating, usually with higher rates ofpenetration and ultimately smoother boreholes.

Rathole1. n. [Drilling] ID: 1537

A storage place for the kelly, consisting of an opening in the rigfloor fitted with a piece of casing with an internal diameter largerthan the outside diameter of the kelly, but less than that of the

upper kelly valve so that the kelly may be lowered into the ratholeuntil the upper kelly valve rests on the top of the piece of casing.

Mousehole1. n. [Drilling] ID: 1492

An opening in the rig floor near the rotary table, but between therotary table and the vee-door, that enables rapid connections whiledrilling. The mousehole is usually fitted underneath with a lengthof casing, usually with a bottom. A joint of drillpipe that will beused next in the drilling operation is placed in the mousehole, boxend up, by the rig crew at a convenient time (immediately after theprevious connection is made). When the bit drills down and thekelly is near the rotary table, another piece of drillpipe must beadded for drilling to continue. This next piece of pipe is standing inthe mousehole when the kelly is screwed onto it. Then the kellyand the joint of pipe in the mousehole are raised to remove the pipefrom the mousehole, the mousehole pipe screwed onto the rest ofthe drillstring, and the drillstring lowered, rotated, and pumpedthrough to continue drilling. Another piece of pipe is put in themousehole to await the next connection.

Blowout1. n. [Drilling] ID: 1224

An uncontrolled flow of reservoir fluids into the wellbore, andsometimes catastrophically to the surface. A blowout may consistof salt water, oil, gas or a mixture of these. Blowouts occur in alltypes of exploration and production operations, not just duringdrilling operations. If reservoir fluids flow into another formationand do not flow to the surface, the result is called an undergroundblowout. If the well experiencing a blowout has significantopenhole intervals, it is possible that the well will bridge over (orseal itself with rock fragments from collapsing formations)downhole and intervention efforts will be averted.

s

Blow out at rig site

BOP (blow out preventer)

Kick1. n. [Drilling] ID: 1454

A flow of reservoir fluids into the wellbore during drillingoperations. The kick is physically caused by the pressure in thewellbore being less than that of the formation fluids, thus causingflow. This condition of lower wellbore pressure than the formationis caused in two ways. First, if the mud weight is too low, then thehydrostatic pressure exerted on the formation by the fluid columnmay be insufficient to hold the formation fluid in the formation.This can happen if the mud density is suddenly lightened or is notto specification to begin with, or if a drilled formation has a higherpressure than anticipated. This type of kick might be called anunderbalanced kick. The second way a kick can occur is if dynamicand transient fluid pressure effects, usually due to motion of thedrillstring or casing, effectively lower the pressure in the wellbore

below that of the formation. This second kick type could be calledan induced kick.

Desander1. n. [Drilling] ID: 1328

A hydrocyclone device that removes large drill solids from thewhole mud system. The desander should be located downstream ofthe shale shakers and degassers, but before the desilters or mudcleaners. A volume of mud is pumped into the wide upper sectionof the hydrocylone at an angle roughly tangent to itscircumference. As the mud flows around and gradually down theinside of the cone shape, solids are separated from the liquid bycentrifugal forces. The solids continue around and down until they

exit the bottom of the hydrocyclone (along with small amounts ofliquid) and are discarded. The cleaner and lighter density liquidmud travels up through a vortex in the center of the hydrocyclone,exits through piping at the top of the hydrocyclone and is thenrouted to the mud tanks and the next mud-cleaning device, usuallya desilter. Various size desander and desilter cones are functionallyidentical, with the size of the cone determining the size of particlesthe device removes from the mud system.

Kelly1. n. [Drilling] ID: 1447

A long square or hexagonal steel bar with a hole drilled through themiddle for a fluid path. The kelly is used to transmit rotary motionfrom the rotary table or kelly bushing to the drillstring, whileallowing the drillstring to be lowered or raised during rotation. Thekelly goes through the kelly bushing, which is driven by the rotarytable. The kelly bushing has an inside profile matching the kelly'soutside profile (either square or hexagonal), but with slightly largerdimensions so that the kelly can freely move up and down inside.

Drawworks1. n. [Drilling] ID: 1352

The machine on the rig consisting of a large-diameter steel spool,brakes, a power source and assorted auxiliary devices. The primaryfunction of the drawworks is to reel out and reel in the drilling line,a large diameter wire rope, in a controlled fashion. The drilling lineis reeled over the crown block and traveling block to gainmechanical advantage in a "block and tackle" or "pulley" fashion.This reeling out and in of the drilling line causes the travelingblock, and whatever may be hanging underneath it, to be loweredinto or raised out of the wellbore. The reeling out of the drillingline is powered by gravity and reeling in by an electric motor ordiesel engine.

Desilter1. n. [Drilling] ID: 1329

A hydrocyclone much like a desander except that its designincorporates a greater number of smaller cones. As with thedesander, its purpose is to remove unwanted solids from the mudsystem. The smaller cones allow the desilter to efficiently removesmaller diameter drill solids than a desander does. For that reason,the desilter is located downstream from the desander in the surfacemud system.

Shale shaker1. n. [Drilling] ID: 1568

The primary and probably most important device on the rig forremoving drilled solids from the mud. This vibrating sieve issimple in concept, but a bit more complicated to use efficiently. Awire-cloth screen vibrates while the drilling fluid flows on top of it.The liquid phase of the mud and solids smaller than the wire meshpass through the screen, while larger solids are retained on thescreen and eventually fall off the back of the device and arediscarded. Obviously, smaller openings in the screen clean moresolids from the whole mud, but there is a corresponding decrease inflow rate per unit area of wire cloth. Hence, the drilling crewshould seek to run the screens (as the wire cloth is called), as fineas possible, without dumping whole mud off the back of theshaker. Where it was once common for drilling rigs to have onlyone or two shale shakers, modern high-efficiency rigs are oftenfitted with four or more shakers, thus giving more area of wirecloth to use, and giving the crew the flexibility to run increasinglyfine screens.

Kill line1. n. [Drilling] ID: 1458

A high-pressure pipe leading from an outlet on the BOP stack tothe high-pressure rig pumps. During normal well controloperations, kill fluid is pumped through the drillstring and annularfluid is taken out of the well through the choke line to the choke,which drops the fluid pressure to atmospheric pressure. If thedrillpipe is inaccessible, it may be necessary to pump heavydrilling fluid in the top of the well, wait for the fluid to fall underthe force of gravity, and then remove fluid from the annulus. Insuch an operation, while one high pressure line would suffice, it ismore convenient to have two. In addition, this provides a measureof redundancy for the operation. In floating offshore operations, thechoke and kill lines exit the subsea BOP stack and run along theoutside of the riser to the surface. The volumetric and frictionaleffects of these long choke and kill lines must be taken into accountto properly control the well.

Choke line1. n. [Drilling] ID: 1287

A high-pressure pipe leading from an outlet on the BOP stack tothe backpressure choke and associated manifold. During well-control operations, the fluid under pressure in the wellbore flowsout of the well through the choke line to the choke, reducing thefluid pressure to atmospheric pressure. In floating offshoreoperations, the choke and kill lines exit the subsea BOP stack andthen run along the outside of the drilling riser to the surface. Thevolumetric and frictional effects of these long choke and kill linesmust be considered to control the well properly.

kelly bushing1. n. [Drilling] ID: 1449

An adapter that serves to connect the rotary table to the kelly. Thekelly bushing has an inside diameter profile that matches that of thekelly, usually square or hexagonal. It is connected to the rotarytable by four large steel pins that fit into mating holes in the rotarytable. The rotary motion from the rotary table is transmitted to thebushing through the pins, and then to the kelly itself through thesquare or hexagonal flat surfaces between the kelly and the kellybushing. The kelly then turns the entire drillstring because it isscrewed into the top of the drillstring itself. Depth measurementsare commonly referenced to the KB, such as 8327 ft KB, meaning8327 feet below the kelly bushing.

Prime mover1. n. [Drilling] ID: 1532

The source of power for the rig location. On modern rigs, the primemover consists of one to four or more diesel engines. Theseengines commonly produce several thousand horsepower.Typically, the diesel engines are connected to electric generators.The electrical power is then distributed by a silicon-controlled-rectifier (SCR) system around the rigsite. Rigs that convert dieselpower to electricity are known as diesel electric rigs. Older designstransmit power from the diesel engines to certain rig components(drawworks, pumps and rotary table) through a system ofmechanical belts, chains and clutches. On these rigs, a smaller

electric generator powers lighting and small electricalrequirements. These older rigs are referred to as mechanical rigs ormore commonly, simply power rigs.

PHPA mud1. n. [Drilling Fluids] ID: 2197

A class of water muds that use partially-hydrolyzed polyacrylamide(PHPA) as a functional additive, either to control wellbore shalesor to extend bentonite clay in a low-solids mud. As a shale-controlmud, PHPA is believed to seal microfractures and coat shalesurfaces with a film that retards dispersion and disintegration. KClis used as a shale inhibitor in most PHPA mud designs. In low-solids muds, PHPA interacts with minimal concentrations ofbentonite to link particles together and improve rheology withoutincreased colloidal solids loading.

PDC bit ( FIXED-CUTTER, POLYCRYSTALLINE

DIAMOND BIT)

1. n. [Drilling] ID: 1514

A drilling tool that uses polycrystalline diamond compact (PDC)cutters to shear rock with a continuous scraping motion. Thesecutters are synthetic diamond disks about 1/8-in. thick and about1/2 to 1 in. in diameter. PDC bits are effective at drilling shaleformations, especially when used in combination with oil-basemuds.

Bit1. n. [Drilling] ID: 1216

The tool used to crush or cut rock. Everything on a drilling rigdirectly or indirectly assists the bit in crushing or cutting the rock.The bit is on the bottom of the drillstring and must be changedwhen it becomes excessively dull or stops making progress. Mostbits work by scraping or crushing the rock, or both, usually as partof a rotational motion. Some bits, known as hammer bits, poundthe rock vertically in much the same fashion as a construction siteair hammer

TRI- CONE BIT

Roller-cone bit1. n. [Drilling] ID: 1549

A tool designed to crush rock efficiently while incurring a minimalamount of wear on the cutting surfaces. Invented by HowardHughes, the roller-cone bit has conical cutters or cones that havespiked teeth around them. As the drillstring is rotated, the bit conesroll along the bottom of the hole in a circle. As they roll, new teethcome in contact with the bottom of the hole, crushing the rockimmediately below and around the bit tooth. As the cone rolls, thetooth then lifts off the bottom of the hole and a high-velocity fluidjet strikes the crushed rock chips to remove them from the bottomof the hole and up the annulus. As this occurs, another tooth makescontact with the bottom of the hole and creates new rock chips.Thus, the process of chipping the rock and removing the small rockchips with the fluid jets is continuous. The teeth intermesh on thecones, which helps clean the cones and enables larger teeth to beused. There are two main types of roller-cone bits, steel milled-tooth bits and carbide insert bits.

Workover1. n. [Drilling] ID: 1666

The repair or stimulation of an existing production well for thepurpose of restoring, prolonging or enhancing the production ofhydrocarbons.

Degasser1. n. [Drilling] ID: 1324

A device that removes air or gases (methane, H2S, CO2 andothers) from drilling liquids. There are two generic types that workby both expanding the size of the gas bubbles entrained in the mud(by pulling a vacuum on the mud) and by increasing the surfacearea available to the mud so that bubbles escape (through the use of

various cascading baffle plates). If the gas content in the mud ishigh, a mud gas separator or "poor boy degasser" is used, becauseit has a higher capacity than standard degassers and routes theevolved gases away from the rig to a flaring area complete with anignition source.

Drillstem test1. n. [Drilling] ID: 1373

A procedure to determine the productive capacity, pressure,permeability or extent (or a combination of these) of a hydrocarbonreservoir. While several different proprietary hardware sets areavailable to accomplish this, the common idea is to isolate the zoneof interest with temporary packers. Next, one or more valves areopened to produce the reservoir fluids through the drillpipe andallow the well to flow for a time. Finally, the operator kills thewell, closes the valves, removes the packers and trips the tools outof the hole. Depending on the requirements and goals for the test, itmay be of short (one hour or less) or long (several days or weeks)duration and there might be more than one flow period andpressure buildup period.

2. n. [Well Testing] ID: 8022

Well tests conducted with the drillstring still in the hole. Oftenreferred to as DST, these tests are usually conducted with adownhole shut-in tool that allows the well to be opened and closedat the bottom of the hole with a surface-actuated valve. One ormore pressure gauges are customarily mounted into the DST tooland are read and interpreted after the test is completed. The toolincludes a surface-actuated packer that can isolate the formationfrom the annulus between the drillstring and the casing, therebyforcing any produced fluids to enter only the drillstring. By closingin the well at the bottom, afterflow is minimized and analysis issimplified, especially for formations with low flow rates. Thedrillstring is sometimes filled with an inert gas, usually nitrogen,for these tests. With low-permeability formations, or where theproduction is mostly water and the formation pressure is too low tolift water to the surface, surface production may never be observed.In these cases, the volume of fluids produced into the drillstring iscalculated and an analysis can be made without obtaining surfaceproduction. Occasionally, operators may wish to avoid surface

production entirely for safety or environmental reasons, andproduce only that amount that can be contained in the drillstring.This is accomplished by closing the surface valve when thebottomhole valve is opened. These tests are called closed-chambertests.

Drillstem tests are typically performed on exploration wells, andare often the key to determining whether a well has found acommercial hydrocarbon reservoir. The formation often is notcased prior to these tests, and the contents of the reservoir arefrequently unknown at this point, so obtaining fluid samples isusually a major consideration. Also, pressure is at its highest point,and the reservoir fluids may contain hydrogen sulfide, so thesetests can carry considerable risk for rig personnel.

The most common test sequence consists of a short flow period,perhaps five or ten minutes, followed by a buildup period of aboutan hour that is used to determine initial reservoir pressure. This isfollowed by a flow period of 4 to 24 hours to establish stable flowto the surface, if possible, and followed by the final shut-in orbuildup test that is used to determine permeability thickness andflow potential.

Rheology1. n. [Geology] ID: 430

Generally, the study of how matter deforms and flows, includingits elasticity, plasticity and viscosity. In geology, rheology isparticularly important in studies of moving ice, water, salt andmagma, as well as in studies of deforming rocks.

2. n. [Drilling Fluids] ID: 2268

The science and study of the deformation and flow of matter. Theterm is also used to indicate the properties of a given fluid, as inmud rheology. Rheology is an extremely important property of

drilling muds, drill-in fluids, workover and completion fluids,cements and specialty fluids and pills. Mud rheology is measuredon a continual basis while drilling and adjusted with additives ordilution to meet the needs of the operation. In water-base fluids,water quality plays an important role in how additives perform.Temperature affects behavior and interactions of the water, clay,polymers and solids in a mud. Downhole pressure must be takeninto account in evaluating the rheology of oil muds.

X-Y plots of rheological models.

Rheology. Fluids are described as Newtonian or non-Newtoniandepending on their response to shearing. Shear stress of aNewtonian fluid (upper left) is proportional to the shear rate. Mostdrilling muds are non-Newtonian fluids, with viscosity decreasingas shear rate increases, and correspond more closely to one of theother three models shown.

Appraisal Wells1. n. [Geology] ID: 35

The phase of petroleum operations that immediately followssuccessful exploratory drilling. During appraisal, delineation wells

might be drilled to determine the size of the oil or gas field andhow to develop it most efficiently.

Reservoir heterogeneities1. n. [Well Testing] ID: 8148

The variations in rock properties in a reservoir. The variations canresult in directional variations in permeability. Geologicalprocesses, such as sedimentation, diagenesis and erosion, act toproduce nonuniformities in rock formations. Because there are somany types of reservoir heterogeneities, a unique interpretation oftest results from pressure data alone is often impossible. Expert testinterpreters rely heavily on experience, core analysis, well logs andknowledge of the geology specific to the region.