United States: Potential Revisions To The API Numbering System

Oil and gas operators understand that each well is identified by a unique "API" number, however many do not understand how the well numbering system in the US works -- nor that changes may be coming. Here is a short course on how the system works and where it may be going.

API Numbers were established by the American Petroleum Institute in 1962 and grew out of the Institute's Well History Control System product which was first offered in 1956. There have been several revisions to the standard, most recently in 1979 in API Bulletin D12A-79. Further modifications to the standard were drafted in 1995, but those revisions were never published or adopted. Thus, the 1979 standard is still in effect, although the publication is no longer available directly from the API.

One of the original recommendations of the API was that the unique identifying numbers should be assigned by state regulatory agencies as part of the oil and gas permitting process. Thus, since January 1967, nearly all API Numbers have been assigned by the regulatory bodies of each state.

Recently, experts have noted that the API numbering system (sometimes referred to as the "D12A" numbering system), in its current form, does not adequately support the oil and gas industry as it is unclear how to apply the standard to modern well configurations such as horizontal or multi-leg drilling. Furthermore, inconsistencies in how the standard is applied in each state creates confusion for operators both in their relations with state agencies and in merging well data from various states.

Currently, an API Number has up to 14 digits. Following is an example of an API Number and explanation of each segment of the number:


42: STATE of the surface location of the well (for example, 42 is Texas; California is 04). The states are numbered alphabetically from 01 (Alabama) through 49 (Wyoming). The District of Columbia is 08 and Alaska and Hawaii, which joined the US after the system was originally created, are 50 and 51, respectively. Codes 52-54 are reserved for future states. Codes above 55 are for offshore federal waters, also called "pseudo-states." Similarly, Canadian provinces and districts are assigned initial codes running from 71 to 89. (Alberta is 71.)

439: COUNTY of the surface location of the well (439 is Tarrant County in Texas; Kern County, California is 029). All of these codes are odd numbers except for certain counties in Arizona, New Mexico and California.

35076: UNIQUE WELL IDENTIFIER for the well. A unique number for a particular well in the identified county. Most wells designated with the identifying number 00000 are pre-API Number wells (historical) and most states use 10000-50000 for current wells. This was meant to be the "parent" well number (i.e. the number for the hole in the ground).

01: DIRECTIONAL SIDETRACK CODE for the wellbore. The original completion is usually coded 00, then 01, 02 and so on for each subsequent bottom-hole location. This was meant to be a wellbore identifier which differentiates each and all wellbores for the "parent" well.

00: EVENT SEQUENCE CODE for the wellbore. This code is meant to be used to indicate if a wellbore has been deepened, recompleted or worked-over.

In 2008 the American Petroleum Institute was approached by Jim Stolle regarding potential updates to the API numbering system. The API indicated that it no longer wished to be the custodian of the API numbering standard set forth in Bulletin D12A, but would consider turning it over to an interested and qualified organization to further its use. The Professional Petroleum Data Management Association (PPDM) asked for API's support in assuming custodianship of the standard and the API accepted. The PPDM is a not for profit, international standards body that has developed data management standards within the oil and gas industry for the past 20 years.

The PPDM is undertaking to:

  1. Work with industry experts, both within and outside of the PPDM membership, to review and revise the D12A well numbering standard.
  2. Where possible, consider and review other existing well numbering standards.
  3. Encourage regulatory agencies, vendors and operators to adopt the revised well numbering standards, and provide mechanisms that will facilitate this process.

    It is recognized that this will be a very long process, and success is not guaranteed.

A PPDM planning committee began meeting in summer 2009 to discuss a revised standard, and the project formally launched in early 2010. The process is still ongoing, but it seems likely that the familiar API standard is likely to be revised over the next year or two. The PPDM hopes to modernize the system to sufficiently account for current drilling methods and technology and gain widespread acceptance by state regulatory bodies and industry. Additional updates may be found at The Professional Petroleum Data Management (PPDM) Association.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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