Definitions and conversion factors

Definitions and conversion factors for oil and gas

A deposit is an accumulation of petroleum in a geological unit, delimited by rocks with stratigraphical or structural boundaries, contact surfaces between petroleum and water in the formation, or a combination of these, so that the petroleum concerned is everywhere in pressure communication through fluid or gas.

A discovery is one or more deposits, which testing, sampling or logging have shown probable mobile petroleum.

A field is one or more discoveries which the licensees have decided to develop and for which the authorities have approved or granted exemption from a Plan for Development and Operation, PDO.

Resources originally in place are resources which, using geological and petroleum technological methods, are calculated to be in place in a deposit prior to start of production.

Originally recoverable resources/reserves are the resources and reserves which can be recovered from a deposit from the start of production to its termination, based on current understanding of the quantities in place and the recovery factor.

Reserves are resources in classes 0, 1 and 2. A distinction is made between originally recoverable reserves and remaining recoverable reserves.

Oil equivalents (abbreviated o.e.) are used when oil, gas and NGL are to be summed. The term is linked to the amount of energy which will be released when these various types of petroleum are burned. Based on typical calorific values for the Norwegian continental shelf, the Directorate uses the following conversion factors:

1000 Sm³ of gas corresponds to 1 Sm³ o.e.
1 Sm³ of oil corresponds to 1 Sm³ o.e.
1 ton of NGL corresponds to 1.3 Sm³ o.e.

1 Sm³ = 6.293 barrels
1 Sm³ = 35.3 cubic feet

Exploration and development wells
Definitions and well terms.
Exploration well is a generic term for wildcat and appraisal wells.
A wildcat well is the first well drilled on a new, clearly defined geological structure (a prospect).
An appraisal well is a well which is drilled to determine the extent and size of a discovery.
A development well is a generic term for wells which are used to produce oil and gas from a field. It covers production wells, injection wells and observation wells.
Well designations consist of the following parts:
0000¹/00²-A³-00⁴A⁵ X⁶ T2⁷
¹ quadrant
² block
³ space for exploration well, A, B, C, etc. denote production installations, U for shallow borehole, T for test production well
⁴ serial number in the block
⁵ A, B, C, etc. for sidetracking (new wells), S for exploration well planned to be drilled inclined, R for re-opened exploration well, H for development well completed on the sea floor
⁶ space, 2, 3, 4, etc. for number of times an exploration well is re-opened, X for well abandoned for technical reasons
⁷ well serial number. The first well path is not denoted (space), thereafter T2, T3, etc.
Examples:

31/2-5 Exploration well

31/2-5 SR2 Exploration well which was planned to be drilled inclined and was then re-opened twice or has been temporarily abandoned

30/9-A-25 AX Development well which was sidetracked from 30/9-A-25 and which failed to reach the reservoir

Success rate can be defined in many ways. Here, we have included all discoveries in resource classes 0-5, i.e. those which are profitable or may be profitable in the long run. If we include the discoveries in class 6, which are not expected to be profitably developed, the success rate will be somewhat higher. This may be called the "technical success rate". It is also common to only consider those discoveries which are developed or are clearly profitable today, i.e. classes 0-3. The success rate will then be lower.

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