1. BASIS OF PREPARATION (CONTINUED) (d) Use of estimates and judgements (continued) (iv) Estimation of oil and gas reserves (continued) Proved reserves are estimated by reference to available reservoir and well information, including production and pressure trends for producing reservoirs and, in some cases, subject to definitional limits, to similar data from other producing reservoirs. Proved reserves estimates are attributed to future development projects only where there is a significant commitment to project funding and execution and for which applicable governmental and regulatory approvals have been secured or are reasonably certain to be secured. Furthermore, estimates of proved reserves only include volumes for which access to market is assured with reasonable certainty. All proved reserves estimates are subject to revision, either upward or downward, based on new information, such as from development drilling and production activities or from changes in economic factors, including product prices, contract terms or development plans. Probable reserves are those unproved reserves which analysis of geological and engineering data suggests are more likely than not to be recoverable. In this context, when probabilistic methods are used, there should be at least a 50% probability that the quantities actually recovered will equal or exceed the sum of estimated proved plus probable reserves. In general, changes in the technical maturity of hydrocarbon reserves resulting from new information becoming available from development and production activities have tended to be the most significant cause of annual revisions. In general, estimates of reserves for undeveloped or partially developed fields are subject to greater uncertainty over their future life than estimates of reserves for fields that are substantially developed and depleted. As a field goes into production, the amount of proved reserves will be subject to future revision once additional information becomes available through, for example, the drilling of additional wells or the observation of longterm reservoir performance under producing conditions. As those fields are further developed, new information may lead to revisions. Changes to the Group’s estimates of proved and probable reserves, particularly proved and probable developed reserves, also affect the amount of depreciation and amortisation recorded for oil and gas assets and rights and concessions related to revisions. A reduction in proved and probable developed reserves will increase depreciation and amortisation charges (assuming constant production) and reduce income. Although the possibility exists for changes in reserves to have a critical effect on depreciation and amortisation charges and, therefore, income, it is expected that in the normal course of business, the Group will continue to prioritise exploration and timely project delivery which ultimately results in maximisation of reserve recovery and will thus constrain the likelihood for changes to occur. Integrated Report 2023 201
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