Oilfield Glossary

D to F

Darcy – a unit of permability. That value which will allow flow of 1 milliliter/sec of 1 centipoise viscosity through 1 cm² under pressure of 1 atmosphere per cm.

Deconvolution – the process of undoing the effect of a filter.

Deepwater – Generally defined as operations in water depths of 1000 ft. or greater.

Deepwater Upper Completions - Offshore wells in water depths greater than 1000 feet are considered "deepwater". These wells are characterized by high drilling and intervention costs. Both "dry tree" and "wet tree" completion methods are common.

Depth migration – special seismic data processing used to focus subsurface events to their proper location in depth. Prestack depth migration, a computing-intensive process, has been highly successful for complex imaging, including subsalt formations.

Desander – a centrifugal device for removing sand from drilling fluid to prevent pump abrasion.

Development well – a well drilled in a proven field to complete a pattern of production.

Deviation – the angle between the wellbore axis (in the direction of the end, or bottom, of the well) and the downward vertical. Deviation values are always positive. Also called Inclination.

Dip – the angle that a refractor or reflector makes with the horizontal. Also, the angle of inclination of a geologic layer or sedimentary bed.

Directional drilling – the method of guiding a well along a predetermined path to a specific target. A directional drilling company provides technology and rig site supervision to efficiently meet directional drilling objectives.

DMO – Dip moveout offset – the difference in arrival times at different seismic detectors due to reflector dip.

Downhole motor - a tool directly above the drill bit in a drill string that converts the hydraulic energy of the circulating drilling fluid into mechanical energy to turn the bit independently of drill string rotation. May include a bent section to perform directional drilling. (See steerable motor)

Downhole oil/water separation – a system comprising a downhole hydrocyclone and electrical submersible pump that separates oil from water downhole, reinjects water, and produces oil to the surface.

Drill bit - the component at the end of the drill string that cuts the rock and makes hole. (See Tricone bit and PDC bit)

Drill collar - heavy-walled sections of pipe included at the bottom of the drill string to apply weight to the drill bit during drilling.

Drill ship - A vessel designed for drilling in deep water without legs or anchors holding it to the sea floor and using dynamic positioning to hold it over the subsea wellhead.

Drill stem – all components in a rotary drilling assembly from the swivel to the bit.

Drill Stem Testing - A method of determining the potential productivity of a subsurface formation in either open or cased hole.

Drill string – the total string of drill pipe with attached tools and bit.

Drill-in fluid – a specialty drilling fluid designed to minimize formation damage in the reservoir.

Drilling fluid – fluid used in the wellbore to lubricate and cool the bit, control bottom-hole pressures, and remove cuttings.

Drilling mud – see drilling fluid

DZO – Demigration to zero offset – in seismic processing an improvement over DMO in situations where velocity varies significantly as a function of depth.

Elastomer – an elastic synthetic rubber or plastic material – often the main component of packing material in downhole packers.

Electrical submersible pump (ESP) – a system comprised of a downhole pump, a downhole electric motor, cabling, and surface controller to lift larger quantities of fluids from wells that do not flow under their own pressure.

Emulsifier – a material that causes water and oil to form an emulsion, i.e.; fine oil droplets suspended in the water.

Expandables - Expandables refers to any of a series of systems and products based on expandable solid tubular, which relies on forcing an expansion device (i.e., mandrel or pig) through standard oilfield tubulars to permanently expand the diameter of the pipe downhole.

Exploration well – a well drilled in search of an undiscovered reservoir or to greatly extend the limits of a known reservoir.

Fishing – the process of recovering equipment lost or stuck in the wellbore. Tools and services that perform specialty and repair work downhole. Fishing activities include retrieving lost tools and repairing wellbore damage.

Float equipment – Check valves that permit fluid to pass downward, but not upward through the casing. A float collar is a special coupling device inserted one or two joints above the bottom of the casing string. A float shoe is positioned at the end of the casing.

Flocculation – the coagulation of solids in a fluid, produced by special additives or contaminants.

Flow Control Equipment - are mechanical devices that use conventional wireline techniques for the express purpose of directing, managing and controlling the flow of produced or injected fluids in the production tubing.

Fluid – a substance which deforms continuously under the action of a shear force, however small. Wellbore fluids include oil and water (with or without gas in solution) and free gas.

Foaming agent – A chemical used in gas wells to lighten the water column to promote gas production. Also, a chemical used while drilling wells with air or gas as the drilling fluid, to force water with the air and cuttings.

Fold – in seismic processing, the number of traces with different source-to-receiver separations summed into a single trace.

FORMation Junction™ – a Baker Oil Tools system using formed metal technology to create a multilateral junction of two 7-in. casing strings, the overall outside diameter (OD) of which is no more than 12.0 in. The technology allows the junction to pass through 13 3/8-in. casing or a 12 1/4-in. open hole. (see multilateral)

Fracturing (frac) – a method of stimulation production by opening new flow channels in the rock surrounding a production well by pumping proppant and fluid into the well at high pressure and volume.

Full Bore Isolation Valve (FBIV) - is a normally closed disc valve, designed to provide isolation within the tubing string, holding pressure from both above and below.