Oil & Gas Terminology

A BHA is the lower section of the drill string, consisting of the drill bit, drill collars, stabilizers, and any special tools used to control the direction and quality of the wellbore.

A DDR is the official daily record of all drilling operations on a well, documenting activities, depths, equipment status, fluid properties, safety observations, and time breakdowns over a 24-hour reporting period.

Directional drilling is the practice of drilling a wellbore along a planned, non-vertical trajectory to reach subsurface targets that are not directly below the surface location.

Dogleg severity is the rate of change in the wellbore trajectory, measured in degrees per 100 feet (or degrees per 30 meters). It quantifies how sharply the wellbore is curving in three-dimensional space and is a critical parameter for well planning, casing design, and BHA component fatigue analysis.

ECD is the effective density exerted by the drilling fluid on the wellbore wall during circulation, equal to the static mud weight plus the annular pressure losses caused by fluid friction. It is the critical parameter for maintaining wellbore stability and preventing lost circulation or kicks.

Lost circulation is the partial or complete loss of drilling fluid into the formation through natural or induced fractures, vugs, or highly permeable zones. It reduces hydrostatic pressure in the wellbore, potentially causing kicks, and is one of the most common and expensive drilling problems worldwide.

LWD is a drilling technology that acquires formation evaluation measurements — such as gamma ray, resistivity, density, and neutron porosity — from sensors in the BHA while the well is being drilled, providing real-time petrophysical data without requiring a separate wireline run.

A motor stall occurs when the downhole mud motor's torque capacity is exceeded, causing it to stop rotating while the drill string continues to pump fluid. It is detected by a sudden spike in standpipe pressure and can damage the motor's elastomer, reducing its useful life and drilling performance.

MWD is a drilling technology that provides real-time measurement of wellbore inclination, azimuth, and toolface orientation from sensors located in the bottom hole assembly, transmitted to the surface during drilling operations.

NPT is any time during drilling operations where no progress is made toward the well's objectives, typically caused by equipment failures, weather delays, wellbore instability, or waiting on services. NPT directly increases well cost without adding value.

ROP is the speed at which the drill bit advances through rock, measured in feet per hour (ft/hr) or meters per hour (m/hr). It is the primary metric for drilling efficiency and directly impacts well cost and cycle time.

A Rotary Steerable System is a downhole directional drilling tool that enables continuous steering of the wellbore while the entire drill string rotates, eliminating the need for sliding with a mud motor. RSS technology delivers superior hole quality, higher ROP, and better hole cleaning compared to conventional motor assemblies.

Stuck pipe is a drilling condition in which the drill string cannot be moved freely — neither rotated nor reciprocated — due to mechanical obstruction, differential pressure, or wellbore geometry issues. It is one of the most expensive and time-consuming problems in drilling operations.

WITSML is an open-source, XML-based data standard for the exchange of drilling, completions, and production data between oilfield service companies, operators, and software systems. It is maintained by Energistics and is the de facto standard for real-time drilling data transfer.

WOB is the downward force applied to the drill bit by the weight of the drill collars and BHA, measured in thousands of pounds (klbs). It is one of the primary controllable parameters for optimizing rate of penetration and bit life.

Artificial lift refers to any method used to increase the flow of oil or gas from a production well when natural reservoir pressure is insufficient to bring fluids to the surface at economic rates.

BSW (Basic Sediment and Water) is the percentage of non-hydrocarbon material — primarily water and fine sediment — present in a crude oil sample. It is a critical quality parameter that directly affects oil pricing, pipeline acceptance, and net revenue calculations.

An Electric Submersible Pump (ESP) is a multi-stage centrifugal pump installed downhole and powered by an electric motor to lift large volumes of fluid from the wellbore to the surface. ESPs are the preferred artificial lift for high-rate wells.

Gas lift is an artificial lift method that injects compressed gas into the production tubing to reduce the hydrostatic pressure of the fluid column, allowing reservoir pressure to push fluids to the surface.

GOR (Gas-Oil Ratio) is the volume of gas produced per barrel of oil, expressed in standard cubic feet per stock tank barrel (scf/STB). It is a fundamental reservoir and production parameter that indicates drive mechanism, depletion stage, and fluid composition.

Plunger lift is an artificial lift method that uses a free-traveling piston (plunger) inside the production tubing to periodically remove accumulated liquids from a gas well, restoring gas flow without external energy input.

A rod pump is an artificial lift system that uses a surface pumping unit, sucker rod string, and downhole plunger pump to mechanically lift fluids from a wellbore to the surface. It is the most common artificial lift method worldwide.

A run ticket is the official document used to record the measurement and transfer of custody of crude oil from a lease storage tank to a purchaser's transport vehicle, serving as the basis for sales accounting and revenue distribution.

Tank gauging is the measurement of liquid levels in field storage tanks to determine the volume of crude oil, produced water, or other fluids on hand at a lease or production facility.

A well test is a controlled measurement of production rates, pressures, and fluid properties from an oil or gas well, used to evaluate reservoir characteristics, establish allocation factors, and determine regulatory compliance.

An AFE (Authorization for Expenditure) is a formal budget document that details the estimated costs of a proposed oil and gas well or project, submitted for management approval before capital is committed. It serves as the financial control document throughout the project lifecycle.

The Arps decline model is a set of empirical equations developed by J.J. Arps in 1945 that describe how oil and gas production rates decrease over time. The three decline types — exponential, hyperbolic, and harmonic — are defined by the b-factor parameter.

Decline Curve Analysis (DCA) is a reservoir engineering technique that uses historical production data to forecast future production rates and estimate ultimate recovery from oil and gas wells by fitting mathematical decline models to observed trends.

IRR (Internal Rate of Return) is the discount rate at which the net present value of all cash flows from an investment equals zero. It represents the annualized rate of return that a project is expected to generate over its economic life.

Monte Carlo simulation is a probabilistic analysis method that uses repeated random sampling from defined input distributions to generate a range of possible outcomes, producing P10, P50, and P90 estimates for reserves, economics, and risk assessment in oil and gas projects.

NPV (Net Present Value) is a financial metric that calculates the present value of all future cash flows generated by an investment, discounted at a specified rate, minus the initial capital expenditure. It is the primary decision criterion for oil and gas investment evaluation.

A petroleum fiscal regime is the set of laws, regulations, and contractual terms that govern how a host government taxes and collects revenue from oil and gas production within its jurisdiction. The fiscal regime determines the government's share of petroleum revenues and directly impacts project economics and investment decisions.

A Production Sharing Contract (PSC) is a petroleum fiscal arrangement where the host government retains ownership of the resource while the contractor finances exploration and development, recovering costs from a portion of production (cost oil) and sharing the remaining production (profit oil) with the government.

A royalty in oil and gas is a payment made to the mineral rights owner — whether a private landowner or sovereign government — calculated as a percentage of gross production revenue, before deduction of operating or capital costs.

A type curve is a representative production profile derived from analog wells that serves as a forecast template for new wells before they have sufficient production history for individual decline curve analysis.

ERP (Enterprise Resource Planning) for oil and gas is an integrated software platform that manages the core business processes of upstream, midstream, or downstream energy companies — including finance, procurement, inventory, human resources, and operations — adapted to the unique requirements of the petroleum industry.

Offshore and onshore operations represent the two fundamental operating environments in oil and gas, differing significantly in drilling methods, production systems, logistics, regulatory requirements, cost structures, and the software systems needed to manage them.

Oilfield inventory management is the tracking and control of equipment, spare parts, consumables, and tubulars across field locations, pipe yards, and warehouses to ensure operational readiness while minimizing excess stock and carrying costs in the oil and gas industry.

Production allocation is the process of distributing total measured production from a commingled facility (tank battery, separator, or pipeline) back to the individual wells that contributed to that production, using well test data, meter readings, or mathematical methods.

SCADA (Supervisory Control and Data Acquisition) is a control system architecture that uses computers, networked data communications, and graphical user interfaces to provide high-level process supervision and real-time monitoring of oil and gas field equipment and infrastructure.