Oil & Gas Glossary 1.0

The increase in bottomhole pressure expressed as an increase in pressure that occurs only when mud is being circulated. Because of friction in the annulus as the mud is pumped, bottomhole pressure is slightly, but significantly, higher than when the mud is not being pumped. ECD is calculated by dividing the annular pressure loss by 0.052, dividing that by true vertical depth, and adding the result to the mud weight.

A laboratory unit used in pilot testing. One gram or pound equivalent, when added to 350 ml of fluid, is equivalent to 1 lb/bbl.

The mass or weight of a substance per unit volume. For instance, the density of a drilling mud may be 10 pounds per gallon (ppg), 74.8 pounds per cubic foot (lb/ft), or 1,198.2 kilograms per cubic meter (kg/m3). Specific gravity, relative density, and API gravity are other units of density.

The atomic or formula weight of an element, compound, or ion divided by its valence. Elements entering into combination always do so in quantities proportional to their equivalent weights.

Volume flow rate of circulating drilling fluid expressed in gallons or barrels per minute

A laboratory unit used for evaluating or testing drilling fluids. One gram of material, when added to 350 milliliters of fluid, is equivalent to 1 pound of material when added to one 42-gal barrel of fluid.

The equipment included in the drilling fluid circulating system of a rotary rig. Basically, the components consist of the mud pump, rotary hose, swivel, drill stem, bit, and mud return line.

Barium sulfate; a mineral frequently used to increase the weight or density of drilling mud. Its relative density is 4.2 (or 4.2 times denser than water). See barium sulfate, mud.

A drilling mud that contains entrained formation gas, giving the mud a characteristically fluffy texture. Then entrained gas in not released before the fluid returns to the well, the weight or density of the fluid column is reduced. Because a large amount of gas in mud lowers its density, gas-cut mud must be treated to reduce the chance of a kick.

1. the ratio of the weight of a given volume of a substance at a given temperature to the weight of an equal volume of a standard substance at the same temperature. For example, if 1 cubic inch of water at 39 degrees F weighs 1 unit and 1 cubic inch of another solid or liquid at 39 degrees F weight 0.95 unit, then the relative density of the substance is 0.95. In determining the relative density of gases, the comparison is made with the standard of air or hydrogen.

A procedure whereby the formation immediately below the casing shoe is subjected to a pressure equal to the pressure expected to be exerted later by a higher drilling glut density or by the sum of a higher drilling fluid density and back-pressure created by a kick.

The cutting or boring element used in drilling oil and gas wells. This bit consists of a cutting element and a circulating element. The circulating element permits the passage of drilling fluid and utilized the hydraulic force of the fluid stream to improve drilling rates. In rotary drilling, several drill collars are joined to the bottom end of the drill pipe column, and the bit is attached to the end of the string of drill collars. Most bits used in rotary drilling are roller cone bits, but diamond bits are also used extensively.

Abbreviation: circulating bottomhole temperature

Circulating member with integral landing nipples

A solution that contains 1 gram-equivalent of a substance per liter of solution.

See relative density

The crew member who handles the upper end of the drill string as it is being hoisted out of or lowered into the hole. He is also responsible for the circulating machinery and the conditioning of the drilling fluid.

The pressure generated by the mud pumps and exerted on the drill stem

The pressure at which a well that has been closed in on a kick is circulated when well-killing procedures are begun

Porous unsized paper for filtering liquids. API filtration test specifies one thickness of 9-cm filter paper Whatman No. 50, S & S No. 576, or equivalent.

1. in mud terminology, refers to the density of a drilling fluid.

A measure of the density of a fluid (such as a drilling mud).

1. a measure of volume for petroleum products in the United States. One barrel is the equivalent of 42 U.S. gallons or 0.15899 cubic meters (9,702 cubic inches). One cubic meter equals 6.2897 barrels.

Abbreviation: radioactive densiometer; fluid-measuring device to measure density.

An accessory attached o the top of the drill pipe or tubing to form a connection with the mud system to permit circulation of the drilling mud. In some cases, it is also a rotating head.

The amount by which drilling fluid density is reduced by entrained formation fluids or air.

A mixture of barium sulfate, chemicals, and water of a unit density between 18 and 22 pounds per gallon

Lead sulfide (PbS). Technical grades (specific gravity about 7) are used for increasing the density of drilling fluids to points impractical or impossible with barite.

To increase the weight or density of drilling fluid by adding weighting material.

The unit weight of fluid, e.g., pounds per gallon.

Well-control fluid that has been reduced in density or unit weight as a result of entrainment of less-dense formation fluids or air

An earthy deposit made up of the siliceous cell walls of one-celled marine algae called diatoms. It is used as an admixture for cement to produce a low-density slurry.

Weight per unit volume of drilling fluid usually expressed in pounds per gallon or pounds per cubic foot. See hydrostatic pressure.

The pressure at which a well is circulated during well-killing procedures after killweight mud has filled the drill stem. This pressure is maintained until the well is completely filled with killweight mud.

Unit chemical weight of solute per million unit weights of solution. The epm of a solute in solution is equal to the ppm (parts per million) divided by the equivalent weight.

An indicator, mounted in the mud circulating system, that measures and indicates the amount of pressure in the drill stem. See drill stem.

A vibrating screen used to remove cuttings from the circulating fluid in rotary drilling operations. The size of the openings in the screen should be carefully selected to be the smallest size possible that will allow 100 percent flow of the fluid. Also called a shaker.

Formation fluid pressure equivalent to about 0.465 pounds per square foot of depth from the surface. If the formation pressure is 4,650 pounds per square inch at 10,000 feet, it is considered normal.

A beam balance consisting of a cup and a graduated arm carrying a sliding weight and resting on a fulcrum. It is used to determine the density or weight of drilling mud.

The amount of pressure exerted inside the drill pipe as a result of circulating pressure, entry of formation pressure into the well, or both.

A very soluble salt used to increase the density of water to points more than double that of water. Normally added to a system first saturated with calcium chloride.

Circulating fluid, one function of which is to force cuttings out of the wellbore and to the surface. Other functions are to cool the bit and to counteract downhole formation pressure. While a mixture of barite, clay, water, and chemical additives is the most common drilling fluid, wells can also be drilled by using air, gas, water, or oil-base mud as the drilling fluid. See mud.

The specific gravity or density of oil expressed in terms of a scale devised by the American Petroleum Institute. The lighter the oil, the greater the gravity; other factors being equal, the higher the API gravity, the better price the oil will bring.

2. the ratio of the mass of a given volume of a substance to the mass of a like volume of a standard substance, such as water or air.

The course of drilling fluid downward through the annulus and upward through the drill stem, in contrast to normal circulation in which the course is downward through the drill stem and upward through the annulus. Seldom used in open hole, but frequently used in workover operations. Also referred to as "circulating the short way," since returns from bottom can be obtained more quickly than in normal circulation.

A measure of the density of a drilling fluid expressed as pounds per gallon, pounds per cubic foot, or kilograms per cubic meter. Mud weight is directly related to the amount of pressure the column of drilling mud exerts at the bottom of the hole.

1. a scale of pressure differences in which there is a uniform variation of pressure from point to point. For example, the pressure gradient of a column of water is about 0.433 pounds per square inch per foot (9.794 kilopascals per meter) of vertical elevation. The normal pressure gradient in a formation is equivalent to the pressure exerted at any given depth by a column of 10 percent salt water extending from that depth to the surface 0.465 pounds per square inch per foot or 10.518 kilopascals per meter).

Density expressed as the ratio of the weight of a volume of substance to the weight of an equal volume of another standard substance. In the case of liquids and solids, the standard is water. In the case of natural gas or other gas materials, the standard is air.

The state in fluid dynamics of a fluid in motion is determined by the type of fluid (e.g., Newtonian, plastic, pseudoplastic, dilatant); the properties of the fluid such as viscosity and density; the geometry of the system; and the velocity. Thus, under a given set of conditions and fluid properties, the fluid flow can be described as plug flow, laminar (called also Newtonian, streamline, parallel, or viscous) flow, or turbulent flow.

A slurry of portland cement and water and sometimes one or more additives that affect either the density of the mixture or its setting time. The portland cement used may be high early strength common (standard), or slow setting. Additives include accelerators (such as calcium chloride), retarders (such as gypsum), weighting materials (such as barium sulfate), lightweight additives (such as bentonite), or a variety of lost circulation materials (such as mica flakes).

The force exerted by a body of fluid at rest. It increases directly with the density and the depth of the fluid and is expressed in pounds per square inch or kilopascals. The hydrostatic pressure of fresh water is 0.433 pounds per square inch per foot of depth (9.792 kilopascals per meter). In drilling, the term refers to the pressure exerted by the drilling fluid in the wellbore. In a water drive field, the term refers to the pressure that may furnish the primary energy for production.