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Well examination schemes – commonly observed weaknesses


OG status:
Fully open
Author unit / section:
Target audience:

 OSD Wells Inspectors, other OSD and HID inspectors conducting inspections of offshore installations, landward oil and gas borehole sites, underground gas storage sites and offshore installation verification schemes

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To brief wells inspectors and other inspectors involved in inspection of offshore installations and oil and gas borehole sites of common weaknesses found when inspecting well operators’ well examination schemes.


Well operators, as duty holders for oil and gas wells, are required to have a scheme of examination for each and every well to verify that it is designed, constructed and maintained in a safe condition throughout its life from initial design to final abandonment. The examination must be carried out by someone who is competent to do so and independent of line management for the well.

Since the introduction of a regulatory requirement for well examinations schemes in 1996 most duty holders’ schemes have been inspected by HSE. These inspections have uncovered weaknesses in schemes that are common to those of many well operators.


Under the Offshore Installation and Wells (Design and Construction, etc) Regulations 1996, regulation 18 requires well-operators to have arrangements in writing for the examination of wells as an independent check to assure the well operator that the well is designed and constructed properly, and that it is maintained adequately thereafter. The arrangements must be in place before design of a well is commenced. The arrangements also apply to wells predating the regulations. A copy of the arrangements and any reports and recommendations arising from them must be kept at a designated address in Great Britain (i.e. England, Scotland or Wales) and for six months beyond the end of the arrangements.

Observed weaknesses

Ownership and responsibility for Scheme

It is a common error to believe the well examiner is responsible for a well examination scheme. Responsibility for the well examination scheme lies squarely with the well operator. Responsibility covers all aspects of the scheme. The well operator is responsible for ensuring that the scheme is in place, for ensuring that the well examiner is both competent and independent, for ensuring that the scheme is and continues to be effective and that suitable action is taken on any recommendations that the well examiner may make. The person with overall responsibility for the scheme should be clearly identified; his roles and responsibilities should be clearly defined.

Inclusion of all wells

Duty holders occasionally miss part of their well inventory from the well examination scheme. Those most frequently omitted include suspended wells or wells on production or injection that have not been worked over for some time. This is especially true of subsea wells inherited from a previous asset owner. Duty holders must ensure that their entire well inventory is covered by the scheme. It is recommended that, on inheriting wells from another well operator, duty holders review the previous well examination scheme and records for each well in question.

Life Cycle of Well

Some well operators’ schemes lack continuity. The purpose of a well examination scheme is to cover the design, construction and ongoing maintenance of the well, continuously throughout its life from initial design to its final plugging and abandonment. With some well operators the well examination scheme is seen as a responsibility of the company’s drilling department. As a consequence once a well has been drilled, completed and handed over to the production department, the well examination scheme ceases to be applied unless and until the drilling department once again takes over the well for a major work-over. Well operators must also ensure that wells on production or injection or suspended are also actively included in the scheme.

Interface with Installation Verification Schemes

The interface between well examination schemes and installation verification schemes must be properly managed. It is an aspect of schemes that is frequently overlooked. There is a potential for gaps to occur between the two schemes. The intent of well examination is to parallel installation verification schemes; they could not be merged because of the different duty holder structure for installations and wells. Nonetheless some well equipment, in particular Xmas trees and blowout prevention equipment, is suitable for inclusion in either scheme. To avoid unnecessary duplication of work, equipment can be covered by either scheme but need not be included in both. Where well equipment is covered by an installation scheme, for example a mobile drilling unit’s blowout preventers, the well operator must satisfy himself as to the adequacy of the installation verification scheme.

All modifications to design and construction of wells

Major modifications arising from full workover of wells are usually fully covered in examination schemes. Other modifications arising from minor well interventions or from tree and wellhead maintenance are often neglected. It is important that the well examiner is informed of all modifications to wells; minor changes, for example to wellhead or tree fittings, can have a significant impact on safety. Drilling and production engineers should be properly briefed to ensure that this happens.

Inclusion of Mobile Equipment

Not all schemes make adequate provision to cover mobile temporary well control equipment. When such equipment, for example a wire-line BOP and lubricator, is installed on a well, it forms part of the pressure containing envelope and must be covered by the well examination scheme. The permanent pressure-containing parts of well, such as casings and well-head, are invariably fully covered by the scheme, while other well control equipment such as drilling BOPs are usually included by the complementary installation verification arrangements. Temporary, portable well control equipment is frequently overlooked by both schemes. It is suggested that well operators issuing contracts for the provision of such equipment should audit the supplier’s arrangements for ensuring that the equipment remains fit for purpose.

Independence of the examiner

Interpretative guidance to the regulations, published by HSE, explains the degree of independence that well examiners must have from those responsible for the design construction and operation of the well. The guidance explains that the well examiner must be independent and separate from the immediate line management of the work that he is examining. Although it is permissible for the well examiner to be an employee of the well operator’s organisation, it is imperative that he has a high degree of impartiality and independence from pressures from the well-operator, especially of a financial nature. Promotion, pay and reward systems must not be allowed to compromise his financial judgement. Some duty holders fail to achieve the level of independence required, usually by appointing a well examiner that has some line responsibility for the design and construction of the well. Few duty holders carry out audits of their schemes to ensure that a suitable level of independence exists

Competence of the examiner

Competence required for a well examiner is explained in the guidance. It should be someone with sound knowledge and experience of the work to be examined. Competence must cover the full life cycle of the well from design to final abandonments and include any well servicing and change in use that may occur during its lifetime. It is recognised that all the competencies required may not reside with one individual and several individuals may be required to cover all of them. The weakness of many schemes is a lack of any procedure to check the competence of the well examiner, for both breadth and depth of knowledge. As with independence, few duty holders carry out audits of their schemes to verify the competence of well examiners.

Information, instruction, training and supervision of staff

A common weakness of schemes is not to fully inform and instruct those staff in the scheme and to consider it solely a matter for the person responsible for the scheme and the examiners themselves. Well operators have overall responsibility for the effectiveness of their well examination schemes. The purpose of such a scheme is to verify that a well complies with the regulations covering its design and construction. To achieve this it is important that everyone who has responsibility for any aspect of well safety is fully conversant with the scheme. Training in the scheme should be provided for all drilling and production engineers involved in the design of well and the development of well programmes. Training should include clear guidance on the type of information that should be fed into the scheme. Similar training should be provided for operators’ drilling and well service supervisors as well as key personnel employed by drilling and well service contractors.

Guidance on ALARP

Well examiners are, in general, given no guidance on the ALARP principle. Regulations on the design and construction of wells are based on the principle of reducing risk to the health and safety of persons from the well or anything in it to as low as is reasonably practicable. The principle is commonly referred to by the acronym ALARP; the term “reasonably practicable” is defined in law. Explanations of ALARP, including information on legal precedents can be found on the HSE website in an item entitled ALARP “at a glance” .

Misunderstandings about the ALARP principle are common in the upstream oil and gas industry and since it is a cornerstone of the regulations for the design and construction of wells it is imperative that well examiners are well grounded in the principle.

Resolution of disputes

There must be clear guidance on the resolution of disputes between the well examiner and the well operator. The person with overall responsibility for the scheme should have the delegated authority to allow him to resolve disputes.


The quality of audits of well examination arrangements is variable. The regulations require the well-operator to review revise the examination arrangements as often as may be appropriate. This requires effective audit of the scheme. It is suggested that audit should cover the compliance with the scheme, the independence and competence of well examiners and the completeness and effectiveness of the examination scheme. Auditing of the scheme should not be a role of the well examiner.

Further information

Further information can be obtained from Head of Discipline – Well Engineering and Operations OSD 2.4.


Updated 2012-03-27