Oil and gas reserves and resource quantification

in Canada As with other mineral resource estimation, detailed classification schemes have been devised by industry specialists to quantify volumes of oil and gas accumulated underground (known as subsurface). These schemes provide management and investors with the means to make quantitative and relative comparisons between assets, before underwriting the significant cost of exploring for, developing and extracting those accumulations. Classification schemes are used to categorize the uncertainty in volume estimates of the recoverable oil and gas and the chance that they exist in reality (or risk that they do not) depending on the resource maturity. Potential subsurface oil and gas accumulations identified during exploration are classified and reported as prospective resources. Resources are re-classified as reserves following appraisal, at the point when a sufficient accumulation of commercial oil and/or gas are proven by drilling, with authorized and funded development plans to begin production within a recommended five years. Reserve estimates are required by authorities and companies, and are primarily made to support operational or investment decision-making by companies or organisations involved in the business of developing and producing oil and gas. Reserve volumes are necessary to determine the financial status of the company, which may be obliged to report those estimates to shareholders and "resource holders" at the various stages of resource maturation. Currently, the most widely accepted classification and reporting methodology is the 2018 petroleum resources management system (PRMS), which summarizes a consistent approach to estimating oil and gas quantities within a comprehensive classification framework, jointly developed by the Society of Petroleum Engineers (SPE), the World Petroleum Council (WPC), the American Association of Petroleum Geologists (AAPG), the Society of Petroleum Evaluation Engineers (SPEE) and the Society of Economic Geologists (SEG). Public companies that register securities in the U.S. market must report proved reserves under the Securities and Exchange Commission (SEC) reporting requirements which shares many elements with PRMS. Attempts have also been made to standardize more generalized methodologies for the reporting of national or basin level oil and gas resource assessments. ==Reserves and resource reporting==

An oil or gas resource refers to known (discovered fields) or potential accumulations of oil and/or gas (i.e undiscovered prospects and leads) in the subsurface of the Earth's crust. All reserve and resource estimates involve uncertainty in volume estimates (expressed below as Low, Mid or High uncertainty), as well as a risk or chance to exist in reality, depending on the level of appraisal or resource maturity that governs the amount of reliable geologic and engineering data available and the interpretation of those data. Estimating and monitoring of reserves provides an insight into, for example, a company's future production and a country's oil & gas supply potential. As such, reserves are an important means of expressing value and longevity of resources. In the PRMS, the terms 'Resources' and 'Reserves' have distinct and specific meaning with respect to oil & gas accumulations and hydrocarbon exploration in general. However, the level of rigor required in applying these terms varies depending on the resource maturity which informs reporting requirements. Oil & gas reserves are resources that are, or are reasonably certain to be, commercial (i.e. profitable). Reserves are the main asset of an oil & gas company; booking is the process by which they are added to the balance sheet. Contingent and prospective resource estimates are much more speculative and are not booked with the same degree of rigor, generally for internal company use only, reflecting a more limited data set and assessment maturity. If published externally, these volumes add to the perception of asset value, which in turn can influence oil & gas company share or stock value. The PRMS provides a framework for a consistent approach to the estimation process to comply with reporting requirements of particularly, listed companies. Energy companies may employ specialist, independent, reserve valuation consultants to provide third party reports as part of SEC filings for either reserves or resource booking. Reserves Reserves reporting of discovered accumulations is regulated by tight controls for informed investment decisions to quantify differing degrees of uncertainty in recoverable volumes. Reserves are defined in three sub-categories according to the system used in the PRMS: Proven (1P), Probable and Possible. Reserves defined as Probable and Possible are incremental (or additional) discovered volumes based on geological and/or engineering criteria similar to those used in estimating Proven reserves. Though not classified as contingent, some technical, contractual, or regulatory uncertainties preclude such reserves being classified as Proven. The most accepted definitions of these are based on those originally approved by the SPE and the WPC in 1997, requiring that reserves are discovered, recoverable, commercial and remaining based on rules governing the classification into sub-categories and the declared development project plans applied. Probable and Possible reserves may be used internally by oil companies and government agencies for future planning purposes but are not routinely or uniformly compiled. Proven reserves Proven reserves are discovered volumes claimed to have a reasonable certainty of being recoverable under existing economic and political conditions, and with existing technology. Industry specialists refer to this category as "P90" (that is, having a 90% certainty of producing or exceeding the P90 volume on the probability distribution). Proven reserves are also known in the industry as 1P. PD reserves are reserves that can be produced with existing wells and perforations, or from additional reservoirs where minimal additional investment (operating expense) is required (e.g. opening a set of perforations already installed). Reasons for assigning a lower probability to recovering Possible reserves include varying interpretations of geology, uncertainty due to reserve infill (associated with variability in seepage towards a production well from adjacent areas) and projected reserves based on future recovery methods. The probabilistic, cumulative sum of proven, probable and possible reserves is referred to in the industry as "3P" (proven plus probable plus possible) where there is a 10% chance of delivering or exceeding the P10 volume.(ibid) Resource estimates Resource estimates are undiscovered volumes, or volumes that have not yet been drilled and flowed to surface. A non-reserve resource, by definition, does not have to be technically or commercially recoverable and can be represented by a single, or an aggregate of multiple potential accumulations, e.g. an estimated geological basin resource. There are two non-reserve resource categories: Contingent resources Once a discovery has been made, prospective resources can be reclassified as contingent resources. Contingent resources are those accumulations or fields that are not yet considered mature enough for commercial development, where development is contingent on one or more conditions changing. The uncertainty in the estimates for recoverable oil & gas volumes is expressed in a probability distribution and is sub-classified based on project maturity and/or economic status (1C, 2C, 3C, ibid) and in addition are assigned a risk, or chance, to exist in reality (POS or COS). Prospective resources Prospective resources, being undiscovered, have the widest range in volume uncertainties and carry the highest risk or chance to be present in reality (POS or COS). At the exploration stage (before discovery) they are categorized by the wide range of volume uncertainties (typically P90-P50-P10). In the PRMS the range of volumes is classified by the abbreviations 1U, 2U and 3U again reflecting the degrees of uncertainty. Companies are commonly not required to report publicly their views of prospective resources but may choose to do so voluntarily. ==Estimation techniques==

The total estimated quantity (volumes) of oil and/or gas contained in a subsurface reservoir, is called oil or gas initially in place (STOIIP or GIIP respectively). The ratio between oil and gas in place and recoverable volumes is known as the recovery factor (RF), which is determined by a combination of subsurface geology and the technology applied to extraction. When reporting oil & gas volumes, in order to avoid confusion, it should be clarified whether they are oil in place or recoverable volumes. The appropriate technique for resource estimations is determined by resource maturity. There are three main categories of technique, which are used through resource maturation to differing degrees: analog (substitution), volumetric (static) and performance-based (dynamic), which are combined to help fill gaps in knowledge or data. Both probabilistic and deterministic calculation methods are commonly used to calculate resource volumes, with deterministic methods predominantly applied to reserves estimation (low uncertainty) and probabilistic methods applied to general resource estimation (high uncertainty). The combination of geological, geophysical and technical engineering constraints means that the quantification of volumes is usually undertaken by integrated technical, and commercial teams composed primarily of geoscientists and subsurface engineers, surface engineers and economists. Because the geology of the subsurface cannot be examined directly, indirect techniques must be used to estimate the size and recoverability of the resource. While new technologies have increased the accuracy of these estimation techniques, significant uncertainties still remain, which are expressed as a range of potential recoverable oil & gas quantities using probabilistic methods. In general, most early estimates of the reserves of an oil or gas field (rather than resource estimates) are conservative and tend to grow with time. This may be due to the availability of more data and/or the improved matching between predicted and actual production performance. Appropriate external reporting of resources and reserves is required from publicly traded companies, and is an accounting process governed by strict definitions and categorisation administered by authorities regulating the stock market and complying with governmental legal requirements. Other national or industry bodies may voluntarily report resources and reserves but are not required to follow the same strict definitions and controls. Analog (YTF) method Analogs are applied to prospective resources in areas where there are little, or sometimes no, existing data available to inform analysts about the likely potential of an opportunity or play segment. YTF is conceptual and is commonly used as a method for scoping potential in frontier areas where there is no oil or gas production or where new play concepts are being introduced with perceived potential. However, analog content can also be substituted for any subsurface parameters where there are gaps in data in more mature reserves or resource settings (below). Volumetric method Oil & gas volumes in a conventional reservoir can be calculated using a volume equation: Recoverable volume = Gross Rock Volume * Net/Gross * Porosity * Oil or Gas Saturation * Recovery Factor / Formation Volume Factor Deterministic volumes are calculated when single values are used as input parameters to this equation, which could include analog content. Probabilistic volumes are calculations when uncertainty distributions are applied as input to all or some of the terms of the equation (see also Copula (probability theory)), which preserve dependencies between parameters. These geostatistical methods are most commonly applied to prospective resources that still need to be tested by the drill bit. Contingent resources are also characterized by volumetric methods with analog content and uncertainty distributions before significant production has occurred, where spatial distribution information may be preserved in a static reservoir model. Performance-based methods Once production has commenced, production rates and pressure data allow a degree of prediction on reservoir performance, which was previously characterized by substituting analog data. Analog data can still be substituted for expected reservoir performance where specific dynamic data may be missing, representing a "best technical" outcome. In order to achieve international goals for decarbonisation, the International Energy Agency said in 2021 that countries should no longer expand exploration or invest in projects to expand reserves to meet climate goals set by the Paris Agreement. == Unconventional reservoirs ==

The categories and estimation techniques outlined in the PRMS above apply only to conventional reservoirs, where oil & gas accumulations are controlled by hydrodynamic interactions between the buoyancy of oil & gas in water versus capillary forces. Such reservoirs are commonly believed to be regionally pervasive that may be interrupted by regulatory or ownership boundaries with the potential for large oil & gas volumes, which are very hard to verify. Non-unique flow characteristics in unconventional accumulations means that commercial viability depends on the technology applied to extraction. Extrapolations from a single control point, and thereby resource estimation, are dependent on nearby producing analogs with evidence of economic viability. Under these circumstances, pilot projects may be needed to define reserves. Any other resource estimates are likely to be analog-only derived YTF volumes, which are speculative. ==See also==

References Notes Working definitions ==External links==