Oil & Gas Glossary 1.0

The ratio of effective permeability to absolute permeability. The relative permeability of rock to a single fluid is 1.0 when only that fluid is present, and 0.0 when the presence of another fluid prevents all flow of the given fluid. Compare absolute permeability, effective permeability.

A measure of the ability of a single fluid to flow through a rock when another fluid is also present in the pore spaces. Compare absolute permeability, relative permeability.

A measure of the ability of a single fluid (such as water, gas, or oil) to flow through a rock formation when the formation is totally filled (saturated) with a single fluid. The permeability measure of a rock filled with a single fluid is different from the permeability measure of the same rock filled with two or more fluids. See effective permeability.

N:a unit of measure of permeability. A porous medium has a permeability of 1 darcy when differential pressure of 1 atmosphere across a sample 1 centimeter long and 1 square centimeter in cross section will force a liquid of 1 centipoise of viscosity through the sample at the rate of 1 cubic centimeter per second. The permeability of reservoir rocks is usually so low that it is measured in millidarcys.

A method of improved oil recovery in which chemicals dissolved in water are pumped into a reservoir through injection wells to mobilize off left behind after primary or secondary recovery and to move it toward production wells. The chemical solution includes surfactants or surfactant-forming chemicals that reduce the interfacial and capillary forces between oil and water, releasing the oil and carrying it out of the pores where it has been trapped. The solution may also contain cosurfactants to match the viscosity of the solution to that of the oil to stabilize the solution and to prevent its absorption by reservoir rock. An electrolyte is often added to aid in adjusting viscosity. Injection of the chemical solution is followed by a slug of water thickened with a polymer, which pushes the released oil through the reservoir, decreases the effective permeability of established channels so that new channels are opened, and serves as a mobility buffer between the chemical solution and the final injection of water.

The ability of a rock to transmit fluid through the pore spaces. - A key influence on the rate of flow, movement and drainage of the fluids. There is no necessary relation between porosity and permeability. A rock may be highly porous and yet impermeable if there is no communication between pores. A highly porous sand is usually highly permeable. A measure of the ease with which a fluid flows through the connecting pore spaces of rock or cement. The unit of measurement is the millidarcy. Fluid conductivity of a porous medium. Ability of a fluid to flow within the interconnected pore network of a porous medium.

A well drilled to permit more effective extraction of oil from a reservoir. Sometimes called a development well. See development well.

A reduction in the permeability of a formation caused by the invasion of water into the pores.

A petroleum- or water-bearing formation of relatively low porosity and permeability.

Preventing the passage of fluid. A formation may be porous yet impermeable if there is an absence of connecting passages between the voids within it. See permeability.

The procedure by which acid flow is confined to the natural permeability and porosity of the formation. Compare fracture acidizing.

A tube extending the effective packer seal bore; used where excessive tubing expansion or contraction is anticipated.

The percentage of the bulk volume of a rock sample that is composed of interconnected pore spaces that allow the passage of fluids through the sample. See porosity.

The reduction of permeability in a reservoir rock caused by the invasion of drilling fluid and treating fluids to the section adjacent to the wellbore. Often call skin damage.

Laboratory analysis of a core sample to determine porosity, permeability, lithology, fluid content, angle of dip, geological age, and probably productivity of the formation.

A percussion tool operated mechanically to give an upward thrust to a fish by the sudden release of a tripping device inside the tool. if the fish can e freed by an upward blow, the mechanical jar can be very effective. Also called a hydraulic jar.

The movement of fluids in a reservoir resulting from the force of gravity. In the absence of an effective water or gas drive, gravity drainage is an important source of energy to produce oil, and it may also supplement other types of natural drive. Also called segregation drive.

A method of killing a well in which the mud level in the pits is held constant while the choke size is reduced and the pump speed slowed. It is not effective, and therefore, is not recommended, because casing pressure increases to the point at which the formation fractures or casing ruptures, and control of the well is lost.

A procedure by which acid is forced into a formation under pressure high enough to cause the formation to crack. The acid acts on certain kinds of rocks, usually carbonates, to increase the permeability of the formation. Compare matrix acidizing.

A sealing device used to close off the annular space around the kelly in drilling with pressure at the surface, usually installed above the main blowout preventers. A rotating head makes it possible to drill ahead even when there is pressure in the annulus that the weight of the drilling fluid is not overcoming; the head prevents the well from blowing out. It is used mainly in the drilling of formations that have low permeability. The rate of penetration through such formations is usually rapid.

A device made up in the drill string that, when actuated, delivers a heavy downward blow to the string. A bumper jar has a hollow body that moves upward when the drill string is picked up. When the string is dropped quickly, the jar body produces a sharp downward blow on the tubing or pipe made up below the jar. If downward blows can free a fish, a bumper jar can be very effective.