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Classification of Reserves
The estimation of reserves of natural gas, gas condensate and crude oil can be broken down into two components: (i) geological reserves, or the quantities of natural gas, gas condensate and crude oil contained in the subsoil and (ii) extractable reserves, or the portion of geological reserves whose extraction from the subsoil as of the date the reserves are calculated is economically efficient given market conditions and rational use of modern extraction equipment and technologies and taking into account compliance with the requirements of subsoil and environmental protection.
The Russian reserves system differs significantly from SEC standards and PRMS standards, in particular with respect to the manner in which and the extent to which commercial factors are taken into account in calculating reserves. Reserves that are calculated using different methods cannot be accurately reconciled.
Russian reserves system
The Russian reserves system is based solely on the analysis of geological attributes. Explored reserves are represented by categories A, B, and C1; preliminary estimated reserves are represented by category C2; potential resources are represented by category C3; and forecasted resources are represented by categories D1 and D2. Natural gas reserves in categories A, B and C1 are considered to be fully extractable. For reserves of oil and gas condensate, a predicated coefficient of extraction is calculated based on geological and technical factors.
Category A reserves are calculated on the part of a deposit drilled in accordance with an approved development project for the oil or natural gas field. They represent reserves that have been analysed in sufficient detail to define comprehensively the type, shape and size of the deposit; the level of hydrocarbon saturation; the reservoir type; the nature of changes in the reservoir characteristics; the hydrocarbon saturation of the productive strata of the deposit; the content and characteristics of the hydrocarbons; and the major features of the deposit that determine the conditions of its development (mode of operations, well productivity, strata pressure, natural gas, gas condensate and crude oil balance, hydro and piezo-conductivity and other features).
Category B represents the reserves of a deposit (or portion thereof), the oil or natural gas content of which has been determined on the basis of commercial flows of oil or natural gas obtained in wells at various hypsometric depths. The type, shape and size of the deposit; the effective oil and natural gas saturation depth and type of the reservoir; the nature of changes in the reservoir characteristics; the oil and natural gas saturation of the productive strata of the deposit; the composition and characteristics of crude oil, natural gas and gas condensate under in-situ and standard conditions and other parameters; and the major features of the deposit that determine the conditions of its development have been studied in sufficient detail to draw up a project to develop the deposit.
Category B reserves are computed for a deposit (or a portion thereof) that has been drilled in accordance with either a trial industrial development project in the case of a natural gas field or an approved technological development scheme in the case of an oil field.
Category C1 represents the reserves of a deposit (or of a portion thereof) whose oil or natural gas content has been determined on the basis of commercial flows of oil or natural gas obtained in wells (with some of the wells having been probed by a formation tester) and positive results of geological and geophysical exploration of non-probed wells.
The type, shape and size of the deposit and the formation structure of the oil- and gas-bearing reservoirs have been determined from the results of drilling exploration and production wells and by those geological and geophysical exploration techniques that have been field-tested for the applicable area. The lithological content, reservoir type and characteristics, oil and natural gas saturation, oil displacement ratio and effective oil and natural gas saturation depth of the productive strata have been studied based on drill cores and geophysical well exploration materials. The composition and characteristics of crude oil, natural gas and gas condensate under in-situ and standard conditions have been studied on the basis of well testing data. In the case of an oil and natural gas deposit, the commercial potential of its oil-bearing fringe has been determined. Well productivity, hydro- and piezo-conductivity of the stratum, stratum pressures and crude oil, natural gas and gas condensate temperatures and yields have been studied on the basis of well testing and well exploration results. The hydro-geological and geocryological conditions have been determined on the basis of well drilling results and comparisons with neighbouring explored fields.
Category C1 reserves are computed on the basis of results of geological exploration work and production drilling and must have been studied in sufficient detail to yield data from which to draw up either a trial industrial development project in the case of a natural gas field or a technological development scheme in the case of an oil field.
Category C2 reserves are preliminary estimated reserves of a deposit calculated on the basis of geological and geophysical research of unexplored sections of deposits adjoining sections of a field containing reserves of higher categories and of untested deposits of explored fields. The shape, size, structure, level, reservoir types, content and characteristics of the hydrocarbon deposit are determined in general terms based on the results of the geological and geophysical exploration and information on the more fully explored portions of a deposit. Category C2 reserves are used to determine the development potential of a field and to plan geological, exploration and production activities.
Category C3 resources are prospective reserves prepared for the drilling of (i) traps within the oil-and-gas bearing area, delineated by geological and geophysical exploration methods tested for such area and (ii) the formation of explored fields which have not yet been exposed by drilling. The form, size and stratification conditions of the assumed deposit are estimated from the results of geological and geophysical research. The thickness, reservoir characteristics of the formations, the composition and the characteristics of hydrocarbons are assumed to be analogous to those for explored fields. Category C3 resources are used in the planning of prospecting and exploration work in areas known to contain other reserve bearing fields.
Category D1 resources are calculated based on the results the region’s geological, geophysical and geochemical research and by analogy with explored fields within the region being evaluated. Category D1 resources are reserves in lithological and stratigraphic series that are evaluated within the boundaries of large regional structures confirmed to contain commercial reserves of oil and natural gas.
Category D2 resources are calculated using assumed parameters on the basis of general geological concepts and by analogy with other, better studied regions with explored oil and natural gas fields. Category D2 resources are reserves in lithological and stratigraphic series that are evaluated within the boundaries of large regional structures not yet confirmed to contain commercial reserves of oil and natural gas. The prospects for these series to prove to be oil-and gas-bearing are evaluated based on geological, geophysical and geochemical research.
The evaluation of natural gas reserves in newly discovered natural gas or oil-and-gas deposits is carried out under the Russian reserves system using the volume method. The volume method determines the volume of reserves by examining the filtration and capacitive parameters of the deposit based on (i) the area of the deposit; (ii) the effective depth of hydrocarbon saturation; and (iii) the porousness of the deposit and the level of saturation of the hydrocarbons, taking into account thermobaric conditions.
The evaluation of natural gas reserves in deposits already under development is carried out under the Russian reserves system using both the volume method and the material balance method. The material balance method takes into account temporal changes in the effective reservoir pressure as a result of the extraction of the hydrocarbons and the resultant influx of water.
In accordance with the Law on Subsoil mineral reserves in Russia are subject to mandatory state examination, and subsoil users cannot be granted a production license with respect to a field that was not examined. The state examination of reserves is conducted by subsidiary organizations of the Federal Agency on Subsoil Use, including the State Reserve Commission, Central Reserve Commission and its regional departments. If the commercial feasibility of certain reserves is approved by any such organization, the reserves are entered in the State Balance of Mineral Products. Once a subsoil user is granted an exploration, development or production license, it is required to file annual statistical reports reflecting changes in reserves. In addition, subsoil users’ reserve reports are submitted annually for examination and approval by the Central Reserve Commission or its regional organizations or, if there has been a substantial change in reserves, by the State Reserve Commission.
Estimation of reserves, as examined by the state expert organizations and reflected in subsoil users’ annual statistical reports, are accumulated in the State Balance of Mineral Products.
SEC standards differ in certain material respects from PRMS standards. The principal differences include the following:
Certainty of Existence. Under PRMS standards, reserves in undeveloped drilling sites that are located more than one well location from a commercial producing well may be classified as proved reserves if there is “reasonable certainty” that they exist. Under SEC standards, it must be “demonstrated with certainty” that reserves exist before they may be classified as proved reserves.
Duration of License. Under PRMS standards, proved reserves are projected to the economic production life of the evaluated fields. Under SEC standards, oil and gas deposits may not be classified as proved reserves if they will be recovered after the expiration of a current license period unless the license holder has the right to renew the license and there is a demonstrated history of license renewal. The Subsoil Resources Law of the Russian Federation provides that a license holder may request an extension of an existing license where extractable reserves remain upon the expiration of the primary term of the license, provided that the license holder is in material compliance with the license. The SEC has not provided definitive guidance on whether in these circumstances such extractable reserves could be considered proved under SEC standards.
Accordingly, information relating to an estimated proved natural gas, gas condensate and crude oil reserves under SEC standards is not necessarily indicative of information that would be reported under SEC standards in an offering document registered with the SEC. In addition, SEC standards do not permit the presentation of reserves other than proved reserves. SEC Regulation S-X Rule 4-10 paragraph (a) defines proved reserves as follows:
Proved oil and gas reserves. Proved oil and gas reserves are the estimated quantities of crude oil, natural gas, and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable in future years from known reservoirs under existing economic and operating conditions, i.e., prices and costs as of the date the estimate is made. Prices include consideration of changes in existing prices provided only by contractual arrangements, but not on escalations based upon future conditions.
(i) Reservoirs are considered proved if economic producibility is supported by either actual production or conclusive formation test. The area of a reservoir considered proved includes:
(A) that portion delineated by drilling and defined by gas-oil and/or oil-water contacts, if any; and
(B) the immediately adjoining portions not yet drilled, but which can be reasonably judged as economically productive on the basis of available geological and engineering data. In the absence of information on fluid contacts, the lowest known structural occurrence of hydrocarbons controls the lower proved limit of the reservoir.
(ii) Reserves which can be produced economically through application of improved recovery techniques (such as fluid injection) are included in the “proved” classification when successful testing by a pilot project, or the operation of an installed program in the reservoir, provides support for the engineering analysis on which the project or program was based.
(iii) Estimates of proved reserves do not include the following:
(A) oil that may become available from known reservoirs but is classified separately as “indicated additional reserves;”
(B) crude oil, natural gas, and natural gas liquids, the recovery of which is subject to reasonable doubt because of uncertainty as to geology, reservoir characteristics, or economic factors;
(C) crude oil, natural gas, and natural gas liquids, that may occur in undrilled prospects; and
(D) crude oil, natural gas, and natural gas liquids, that may be recovered from oil sales, coal, gilsonite and other such sources.
Proved developed oil and gas reserves. Proved developed oil and gas reserves are reserves that can be expected to be recovered through existing wells with existing equipment and operating methods. Additional oil and gas expected to be obtained through the application of fluid injection or other improved recovery techniques for supplementing the natural forces and mechanisms of primary recovery should be included as “proved developed reserves” only after testing by a pilot project or after the operation of an installed program has confirmed through production response that increased recovery will be achieved.
Proved undeveloped reserves. Proved undeveloped oil and gas reserves are reserves that are expected to be recovered from new wells on undrilled acreage, or from existing wells where a relatively major expenditure is required for recompletion. Reserves on undrilled acreage shall be limited to those drilling units offsetting productive units that are reasonably certain of production when drilled. Proved reserves for other undrilled units can be claimed only where it can be demonstrated with certainty that there is continuity of production from the existing productive formation. Under no circumstances should estimates for proved undeveloped reserves be attributable to any acreage for which an application of fluid injection or other improved recovery technique is contemplated, unless such techniques have been proved effective by actual tests in the area and in the same reservoir.
While the Russian reserves system focuses on the actual physical presence of hydrocarbons in geological formations, and reserves are estimated based on the probability of such physical presence, PRMS standards take into account not only the probability that hydrocarbons are physically present in a given geological formation but also the economic viability of recovering the reserves (including such factors as exploration and drilling costs, ongoing production costs, transportation costs, taxes, prevailing prices for the products, and other factors that influence the economic viability of a given deposit).
Under PRMS standards, reserves are classified as “proved,” “probable” and “possible,” based on both geological and commercial factors.
Proved reserves include reserves that are confirmed with a high degree of certainty through an analysis of the development history and/or volume method analysis of the relevant geological and engineering data. Proved reserves are those that, based on the available evidence and taking into account technical and economic factors, have a better than 90% chance of being produced.
Probable reserves are those reserves in which hydrocarbons have been located within the geological structure with a lesser degree of certainty because fewer wells have been drilled and/or certain operational tests have not been conducted. Probable reserves are those reserves that, on the available evidence and taking into account technical and economic factors, have a better than 50% chance of being produced.
Possible reserves are those unproven reserves that, on the available evidence and taking into account technical and economic factors, have a 10% chance of being produced.
An evaluation of proved, probable and possible natural gas reserves naturally involves multiple uncertainties. The accuracy of any reserves evaluation depends on the quality of available information and engineering and geological interpretation. Based on the results of drilling, testing and production after the audit date, reserves may be significantly restated upwards or downwards. Changes in the price of natural gas, gas condensate or crude oil may also affect our proved and probable reserves estimates, as well as estimates of its future net revenues and net present worth, because the reserves are evaluated, and the future net revenues and net present worth are estimated, based on prices and costs as of the audit date.