англ тэк

(334)jective to identitential, which is defined as fol-

Definition of Occurrences

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—Financial Analysis: capital cost, cashflow forecast, investment cost, inflation forecast, operating cost, sensitivity studies, closure cost, rehabilitation cost.

—Risk Assessment.

A sensitivity study may require independent verification in certain circumstances.

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Урок 4

СРАВНИТЕЛЬНЫЙ АНАЛИЗ СИСТЕМ КЛАССИФИКАЦИИ ЗАПАСОВ И РЕСУРСОВ НЕФТИ И ГАЗА, ПРИНЯТЫХ В РОССИИ И ЗА РУБЕЖОМ

RESERVES/RESOURCE CLASSIFICATIO> SCHEMES USED I> RUSSIA A>D WESTER> COU>TRIES:

A REVIEW A>D COMPARISO>

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RESERVES/RESOURCE CLASSIFICATIO> SCHEMES USED I> RUSSIA A>D WESTER> COU>TRIES:

A REVIEW A>D COMPARISO>

Introduction

The international oil industry currently uses a number of schemes for hydrocarbon reserves and resources classification. These serve different purposes, and are used variously by Governmental agencies, oil companies, scientific societies, research institutes and by the US Securities and Exchange Commission. Although the schemes have many features in common, much attention has been paid in recent years to the development of a single, universal classification.

Russia, unlike many other countries, uses only one reserves classification scheme. Interest is growing in the comparison of the Russian scheme with those used elsewhere. A number of Russian oil and gas companies (e. g. Lukoil, Yukos and Gazprom) have already introduced Western standards for reserves evaluation in order to facilitate foreign investment. Conversely, Western companies operating in the Russian Federation are translating the Russian classification scheme into more familiar terms and definitions.

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THE RUSSIA> RESERVES A>D RESOURCES CLASSIFICATIO> OF HYDROCARBO>

Use of the «Provisional Classification of Oil and Gas Reserves» (adopted by Government ordnance in early 2001) is mandatory in subsurface minerals exploration and development throughout the Russian Federation. According to this scheme, subsurface petroleum and associated components can be divided into reserves and

resources.

Reserves comprise oil, gas and condensate etc. present in discovered accumulations; and resources consist of oil, gas and condensate etc. in accumulations which may be discovered in the future: their presence is implied from the results of geological, geophysical and geochemical surveys.

Hydrocarbon reserves/resources which may have commercial value can be divided into geological reserves (resources), which comprise the oil, gas and condensate in place; and recoverable reserves (resources), which consist of that proportion of the oil and gas in place which can be commercially recovered at the time the estimate was made under market conditions with the use of modem production equipment, and with due regard to environment protection.

The initial volume of oil, gas and condensate in place (i. e. prior to commercial production) is known as the total initial resources (TIR). The TIR is composed of past production together with current reserves in discovered fields (i. e. categories A, B, C1 and С2); plus potential resources (category C3) and hypothetical resources (categories D1, D1+2). Within the TIR, total current resources (TCR) can be distinguished and are made up of reserves in discovered fields together with potential and hypothetical resources. Hydrocarbon reserves can be further divided into categories according to their stage of development, as follows (Table 1): categories А, В and C1 are explored; while category С2 is tentatively evaluated.

Likewise, oil and gas resources are divided into categories which are referred to as potential (Сз), hypothetical localized (D1) and hypothetical (D1 and D2). These definitions are based both on the stage of exploration and also on the reliability of the estimates. The relia-

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bility is not defined in quantitative terms but is defined according to a list of requirements set up for each individual category.

Unlike Western procedures for reserves estimates and stocktaking, the Russian classification scheme breaks both geological and recoverable reserves down into categories. Thus explored reserves (categories A, B, and C1) are used in production planning and in defining oil and gas production levels in explored fields and in fields under production. Tentatively evaluated (C1) reserves define the upside potential of a field, and are used as a basis for the further appraisal of oil and gas discoveries. Potential or Сз resources are used in the preparation of exploration programmes, and in planning the development of reserves in the C1 and C2 categories. Hypothetical localized or DI resources are used as a basis on which to plan geophysical surveys, and to prepare previously identified prospects for wildcat drilling.

Hypothetical resources (D1) are used to justify previouslyidentified leads and plays for further exploration, and in preparing long-term production plans. And the presence of hypothetical resources (D2) — the least well known — is merely implied from general geological concepts and by analogy with other areas; this category is used in planning regional exploration programmes and in identifying primary plays for reconnaissance exploration.

This provisional classification scheme is very similar to the scheme which was introduced in 1983 during the era of centralized planning and state regulation of the national economy. The 1983 scheme was successfully used for strategic development planning, in the preparation of economic and social development plans, in the planning of exploration campaigns, and in the design of oil and gas production facilities. It is adequate for purposes of oil and gas exploration and resource management. However, in the presentday market economy, the resource and reserves categories require some modification.

The new classification, in common with the previous one, is deterministic. However, as effective resource management and exploration planning must integrate commercial risk, the new classification also provides for probabilistic estimates.

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THE >ORWEGIA> PETROLEUM DIRECTORATE RESOURCE MA>AGEME>T CLASSIFICATIO>

The Norwegian Petroleum Directorate (NPD) classification is intended to meet the changing needs of Government to overview and control Norwegian petroleum resources. The basis of the scheme is to classify the originally-recoverable resources of a field or a discovery into one of 12 classes which are differentiated in terms of their place in the development chain (Table 2). Unlike the Russian scheme, the Norwegian scheme only applies to recoverable reserves and resources, and the oil in place is not classified. Furthermore, categories of reserves and resources in the NPD classification are not related to the stage of exploration, as is the case in the Russian classification.

The main definitions in the NPD classification scheme are as follows:

Reserves are defined as those quantities of petroleum which are either already produced (class 2), or which it is anticipated can be commercially recovered from known accumulations from a given date forward (class 3). The term «resources» applies to the hydrocarbons in accumulations which will be discovered in the future (classes 7 to 11), as well those in previously-discovered accumulations which are not planned for commercial production in the next two years (classes 3 to 6). It should be noted that the classification also provides for resource class 8, which consists of hydrocarbons to be recovered by the introduction of new measures for enhanced recovery.

An important feature of the NPD classification is that it provides for probabilistic methods for reserves and resources calculations, and the following concepts are used: a minimal estimate (downside potential) refers to the quantity of hydrocarbons whose certainty is no less than 90 %; a maximal estimate (upside potential) refers to the quantity of hydrocarbons whose certainty is more than 10 %; while a base estimate can be found by either deterministic or probabilistic methods; in the latter case, its certainty is 50 %.

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It is important that probabilistic estimates (minimal, maximal and base) are not only shown in the reports that oil companies submit to the NPD, but are also included in the Norwegian State Registry.

The Statoil classification scheme.

In its annual reports to the NPD on the status of reserves and resources, Statoil uses the NPD classification scheme. But for inhouse estimates and reserves stock-taking, it uses a proprietary classification which identifies ten resource categories (Table 3). The Statoil and NPD classifications use the same methodologies and have many features in common.

For each resource class in a field, basic resources are identified as those which can be produced without special measures such as enhanced recovery (these are marked with an F in Table 3); additional resources which can be produced using enhanced recovery methods are also identified, and these are marked with an M.

THE SECURITY A>D EXCHA>GE COMMISSIO>

CLASSIFICATIO> SCHEME.

The US Security and Exchange Commission (SEC) plays an important role in reserves definitions, and companies wishing to access capital markets in the USA have to comply with SEC regulations. A characteristic feature of the SEC classification is that it is targeted on conservative estimates to minimize risk to shareholders, so the SEC definitions are stricter than most others.

SEC regulations define only the proved reserves. Resources are not defined and not used in economic evaluations. 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 of estimate). Reserves which can be produced economically through application of improved recovery techniques (such as fluid injection) are included in the «proved» category when successful testing by a pilot project, or

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the operation of an installed programme in the reservoir, provides support for the engineering analysis on which the project or programme was based.

THE SPE, WPC A>D AAPG

JOI>T CLASSIFICATIO> SCHEME

The World Petroleum Congresses (WPC) and the Society of Petroleum Engineers (SPE) published a joint Reserves Definition in 1997. This was followed by publication of the Petroleum Resource Classification issued jointly by SPE, WPC and The American Association of Petroleum Geologists (AAPG) in 2000. These organizations represent worldwide professional interests, so the joint classification scheme was an important step towards developing a single scheme which could be used as a universal standard for the geological and economic evaluation of oil and gas resources. Some of the definitions used in the joint scheme are discussed below.

Total petroleum-initially-in-place is that quantity of petroleum which is estimated, on a given date, to be contained in known accumulations, plus those quantities already produced therefrom, plus those estimated quantities in accumulations yet to be discovered. In essence, this definition corresponds to the Total Initial Resources of the Russian classification.

Discovered petroleum-initially-in-place is that quantity of petroleum which is estimated, on a given date, to be contained in known accumulations, plus those quantities already produced therefrom. The discovered petroleum-initially-in-place can be subdivided into «commercial» and «sub-commercial» categories, with the estimated potentially recoverable portion being classified as reserves and contingent resources, respectively («non-commercial» in Russian terminology).

Reserves are defined as those quantities of petroleum which are anticipated to be commercially recovered from known accumulations from a given date forward.

Contingent resources are those quantities of petroleum which are estimated, on a given date, to be potentially recoverable from known accumulations, but which are not currently considered to be

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commercially recoverable. Contingent resources may include, for example, accumulations for which there is currently no viable market, «of where commercial recovery is dependent on the development of new technology.

Undiscovered petroleum-initially-in-place is that quantity of petroleum which is estimated, on a given date, to be contained in accumulations yet to be discovered. The estimated potentially recoverable portion of undiscovered petroleum-initially-in-place is clas-

sified as prospective resources.

The range of uncertainty reflects a reasonable range of estimated potentially recoverable volumes for an individual accumulation. Any estimation of resource and reserves quantities in an accumulation is subject to both geological, technical and commercial uncertainties, and should, in general, be quoted as a range defined as follows:

Low Estimate — proved reserves (IP),

Best Estimate — proved plus probable reserves (2P),

High Estimate — proved plus probable plus possible reserves

(3P),

The SPE, WPC and AAPG classifications allow for probabilistic methods; therefore, in general, there should be at least a 90 % probability that the quantities actually recovered will equal or exceed the Low Estimate. The Best Estimate corresponds to 50 % probability. In addition, a probability value of 10 % should, in general, be used for the High Estimate.

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DISCUSSIO>

The above comparison of classification schemes demonstrates that they have many common features. The principal concepts in each classification are reserves and resources. It should be noted that all the schemes clearly distinguish hydrocarbons in accumulations which are yet to be discovered (undiscovered in the SPE classification, and classes 8, 9, 10 and 11 in the NPD classification), and

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