Part 15. Glossary

Abandoned well:
a well whose use has been permanently discontinued and has been plugged.
Annulus:
the space between two casings, between a casing and the tubings or between the casing and the adjacent formations.
Aquifer:
any stratum or zone below the surface of the earth capable of producing water from a well.
Blowout:
the uncontrolled flow of oil, gas or water from a geological formation that a drilled hole has penetrated.
Blowout Preventer (BOP):
a stack or assembly of valves and equipment attached to the top of the casing during drilling or workover operations to control well pressure.
Bottomhole:
the lowermost portion of the well.
Brine:
saline water naturally occurring in porous sedimentary rock formations; fluid resulting from the dissolution of salt formations with fresh water for the purposes of salt solution mining.
Brine Well:
a well used for dissolving salt from a salt formation, adding brine to, or taking brine from a salt cavern.
Brining (solution mining):
the process of dissolving salt formations using fresh water pumped and circulated into and through wells for the purposes of salt solution mining.
Cable Tool Drilling:
a method of drilling where a heavy metal bit is repeatedly raised and dropped to fracture rock by percussion, thereby drilling a well.
Casing:
metallic or non-metallic pipe placed in the bore hole for the purpose of supporting the sides of the bore and to act as a barrier preventing subsurface migration of fluids out of or into the bore hole e.g. protection of fresh water zones.

Conductor Casing or Drive Pipe:
the initial pipe, usually metallic, used to seal off near-surface or shallow water, prevent the caving or sloughing of overburden into the hole, and as a conductor of the drilling mud through loose, unconsolidated shallow layers of sand, clays, and shales into the well bore.
Surface Casing:
a string of pipe installed into the bore hole, usually metallic and the first string of pipe run into bedrock and cemented in place.
Intermediate Casing:
a string of pipe installed into the bore hole inside the surface casing and cemented in place. The length of the intermediate casing is such that it serves to seal-off any fluid bearing zones, secondary production zones or incompetent rock formations prior to drilling into the target zone. It is also used for the purposes of well control and blowout preventers are installed on it prior to drilling ahead into the target zone.
Production Casing:
a pipe, usually metallic, placed into the borehole and cemented into place inside intermediate casing. The length of the production casing is such that it ends at, or into the producing formation or the storage zone.
Casing Inspection Log:
a log or combination of logs which:
  1. determines the percent penetration of anomalies;
  2. distinguishes between external and internal corrosion; and
  3. detects holes, pits, perforations, metal loss and metal thickness.
Casing Shoe:
a reinforcing collar of steel screwed onto the bottom joint of casing to prevent abrasion or distortion of the casing as it forces its way past obstructions on the wall of the bore hole.
Cathodic Protection:
an electro-chemical, anti-corrosion technique for protection of metal structures such as well casings, pipelines, tanks, buildings whereby weak electric currents are set up to offset the current associated with metal corrosion.
Cementing:
the operation whereby a cement slurry is pumped and circulated down a well through the center of the casing and then upwards into the annular space behind the casing in order to firmly fix the casing in the hole and to buttress the casing string from formation, production or injection pressures and to protect the casing from corrosion due to exposure to formation fluids.
Centralizer:
a casing accessory installed on the outside of a casing string to center the casing string inside the borehole or larger casing;
Communication:
the passage of hydrocarbons or waters through porous and permeable connections from one reservoir to another in a single formation; from formation to formation; or from any formation to any ground water aquifer or to the surface;
Connate Water:
water trapped within the interstices of a sedimentary rock at the time the rock was deposited.
Drill Sump or Pit:
an excavation below ground level, constructed for the purpose of circulating drilling fluids during well drilling operations.
Drilling Mud:
a mixture of clay, water and chemical additives circulated into a well bore during the drilling a well by injection in the drill pipe and through the drill bit to control formation pressure, to lubricate the drill pipe, keep the drill bit cool and to transport the drilled material to the surface.
Flow Rate:
the volume measure of the flow of a fluid per unit of time through an orifice, pump, turbine, conduit or channel.
Fluid:
any material or substance which flows or moves and which is in a semisolid, liquid, sludge, or gas state.
Formation:
a body of rock characterized by a degree of homogeneous lithology that forms an identifiable geologic unit that can be mapped on the earth's surface or is traceable in the subsurface.
Fracturing:
a method of stimulating production or improving deliverability from a formation by inducing fractures and fissures in the formation by applying an external force either through hydraulic pressure or explosive force to the face of the target formation.
Fracture Gradient:
the pressure gradient, if applied to subsurface formations, will cause the formations to physically fracture.
Gradient (operating):
the pressure gradient (pressure at casing seat/metre of overburden) existing during cavern operation and is a function of the mode of operation (brine/hydrocarbon injection/withdrawal), the rate of fluid injection or withdrawal and its relative density and the tubing/casing string sizes.
Gradient (pressure):
the ratio of pressure per unit depth.
Injection Well:
a well into which fluids other than the fluids associated with active drilling operations are being injected
Liner (casing):
casing installed within production casing normally for remedial repairs.
Lithology:
the study or characterization of rock formations.
Neat Cement:
is cement that does not contain any extenders or density reducing additives that affect the curing time and compressive strength of the cement.
Overburden:
loose or unconsolidated sediments, which overlie lithified rock formations.
Packer:
an expanding plug used in a well to seal off certain sections of the tubing or casing when cementing, acidizing, or when a production formation is to be isolated. Packers are run on the tubing or the casing, and when in position can be expanded mechanically or hydraulically against the pipe wall or the wall of the well bore.
Permeability:
the degree of connectivity of the pore spaces within reservoir rock which facilitates the movement of fluids through it; a measure of the rock's capacity to transmit fluids.
Porosity:
the state or quality of being porous; the volume of the pore space within a formation expressed as a percent of the total volume of the rock mass containing the pores.
Preflush:
one or more separate volumes of fluid that are pumped ahead of the cement as a compatible buffer between the cement and drilling fluid and to clean the drilling mud from the annulus in preparation for cementing.
Reservoir:
a porous, permeable sedimentary rock formation containing quantities of hydrocarbons enclosed or surrounded by layers of less permeable or impervious rock; a structural trap; a stratigraphic trap.
Rotary Drilling:
drilling a borehole for a well with a drill bit attached to joints of hollow drill pipe which are rotated to accomplish penetration of rock formations.
Salt Formation:
a rock formation comprised of predominantly sodium chloride deposits which is generally impervious to liquid or gaseous hydrocarbons, has compressive strength comparable to that of concrete, moves plastically to seal fractures or voids, and can be easily mined by dissolution with water.
Salt Cavern:
a cavern constructed within a soluble rock formation, commonly rock salt, by circulating fresh water in a controlled manner for the purposes of creating an underground hydrocarbon storage chamber.
Salt Dome:
a domed-shaped incursion of salt into overlying formations caused by low-density salt deposits rising through higher density formations overlying the salt deposit.
Shoe Joint:
a short section of casing, usually the bottom joint of the string, bounded by the casing shoe and the float collar which is used to contain the tail end cement slurry.
Shut-in Pressure:
the pressure recorded at the wellhead or subsurface when valves are closed to shut-in the flow from or injection into the well.
Solution Mining:
the process of injecting fluid through a well to dissolve rock salt or other readily soluble rock or mineral and production of the artificial brine so created.
Spud:
with respect to a well, means the commencement of actual drilling of the well’s surface casing hole using a cable tool or rotary drilling rig, but does not include activities to prepare a site for drilling the well, including the installing of conductor pipe.
Stimulate or Stimulation:
the treating of a well bore by any chemical or mechanical method such as acidizing, fracturing, perforating or solvent treatment to increase production, injection or recovery of oil, gas, brine or any other substance.
TD Date:
means the date when the drilling of a well reaches the total depth of the well.
TD:
the total depth of a well.