All about Reserves Estimation

Well Test Analysis, Pressure and Production Monitoring........ etc.

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adrian
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Solution Gas

Solution gas, also (incorrectly) called casinghead gas,* is natural gas that is dissolved in reservoir oil under reservoir conditions of pressure and temperature and is liberated from solution by reduction in pressure and temperature as the oil is produced through surface gas-oil separation equipment.

* Casinghead gas is gas produced from an oil well, which may include both solution gas and gas cap gas.
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Lease Condensate

Lease condensate (also called condensate or distillate) is a hydrocarbon liquid
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Classifications of Reserves

Background



Over the years, there have been numerous classifications of oil and gas reserves advocated by various individuals and organizations. The principal purposes of aclassification system are to (1) promote uniformity and (2) identify the degree of risk for each class of reserve. Unfortunately, the terms reserves and resources have been used interchangeably, which has caused confusion.
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Post by FANARCO »

adrian,

Could you please post the reserve categories according to SPE
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Post by zeyadaam »

Adrian, thanks a lot for this informative post!
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Post by adrian »

zeyadaam wrote:Adrian, thanks a lot for this informative post!
You are welcome dear,,,

Follow this topic and i will provide more
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Lahee’s Classification

Among the earliest classifications of reserves were those advocated by Lahee at the 1944 meeting of the American Petroleum Institute (API) and in 1955 at the World Petroleum Congress. As shown in Table 1 , Lahee’s 1955 system classified reserves as proved, probable, possible, or hypothetical.

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From this table, it may be noted that the term reserves was used to include oil and gas yet to be discovered (clause C.2 in the definitions). As discussed below, current practice generally is to restrict usage of the term reserves to the hydrocarbons in discovered accumulations that are commercially recoverable. There are situations, however, where possible reserves might be assigned to untested prospects in a trend of proved production.
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The McKelvey Box

The basis for current terminology for the classification of reserves and resources of all minerals, including oil and gas, is based on work by McKelvey (1972), a former director of the United States Geological Survey (USGS). As shown by Table 2 , which illustrates what has been called a "McKelvey box," resources are assigned two attributes: (1) degree of geologic assurance and (2) feasibility of economic-i.e., commercial — recovery

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Table 2
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Where there is a high degree of geologic assurance regarding the resource, it is classified as identified (or discovered). Conversely, where there is a low degree of geologic assurance, the resource is classified as undiscovered. Reserves are that part of the resource base that has been discovered and for which there is a high feasibility of commercial recovery. The classifications promulgated by the Society of Petroleum Engineers (1987), which are discussed below, are identified in boldface type in Table 2 .
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Post by adrian »

In the context of oil and gas, preferred terminology for resources and reserves is illustrated by Figure 1 , which is adapted from a comparable figure used by the Energy Information Administration of the United States Department of Energy (USDOE/EIA).

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Figure 1[/align]

The term "recoverable resources" is equivalent to the reservoir engineer’s term "ultimate recovery." The term ultimate recovery carries no implication as to whether these volumes are considered proved, probable, or possible reserves. Reserves are time dependent; thus, when reporting reserves, the "as of" date should always be stated. Otherwise, the term original reserves or ultimate recovery should be used.
In the context of this terminology, the term "recoverable reserves" is redundant since the term "reserves" implies recoverable. The term "in-place reserves" is ambiguous; the preferred term is "in-place resources."
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Society of Petroleum Engineers

In 1987 the Society of Petroleum Engineers (SPE) promulgated definitions for proved, probable, and possible reserves of crude oil, condensate, natural gas, natural gas liquids, and "associated substances." Associated substances include sulfur, helium, and carbon dioxide, which may be associated with naturally occurring petroleum deposits, and which may be of sufficient commercial value to warrant extraction and sale as separate products. (The SPE also promulgated definitions prior to 1987; these definitions, however, were for proved reserves only and were in close agreement with definitions promulgated by the American Petroleum Institute.)


Table 3 is a matrix that identifies the terminology for possible combinations of reserve classification, development status, and producing category that are implied in the SPE definitions.

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Table 3[/align]

For example, the term "producing" identifies a well category, not necessarily a reserve classification. There are circumstances that warrant assigning both proved and probable reserves to a producing well.


The United States Securities and Exchange Commission (SEC) also has promulgated definitions for reserves (USA Federal Securities Laws 1982). These definitions, however, are for proved reserves only, as the SEC does not require public companies to report other classes of reserves. For reserves attributable to improved recovery methods, the current SEC definitions are more restrictive than those of the SPE. The SEC definitions require that an improved recovery technique must be proved effective in the "same reservoir." The SPE definitions, however, require "successful testing" in the reservoir or "one in the immediate area with similar rock and fluid properties."

It is apparent that to classify reservoir volumes as proved, they must be in reasonable proximity to productive wells in the same reservoir. The definitions allow utilization of geophysical data to define only possible reserves. This reliance on subsurface (well) data, to the exclusion of geophysical data, to define proved reserves may not be consistent with recent advances in geophysical methods of reservoir definition. Thus, reserve estimators may have to exercise considerable judgment in classifying reserves in newly developing fields where modern geophysical methods have been incorporated in the subsurface interpretation.

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Reserve Definitions and Classifications

(Reserve definitions approved by the Board of Directors, SPE, Inc. Feb. 27, 1987.)

Reserves

Reserves are estimated volumes of crude oil, condensate, natural gas, natural gas liquids, and associated substances anticipated to be commercially recoverable from known accumulations from a given date forward, under existing economic conditions, by established operating practices, and under current government regulations. Reserve estimates are based on interpretation of geologic and/or engineering data available at the time of the estimate.


Reserve estimates generally are revised as reservoirs are produced, as additional geologic and/or engineering data become available, or as economic conditions change.


Reserves do not include volumes of crude oil, condensate, natural gas, or natural gas liquids being held in inventory. If required for financial reporting or other special purposes, reserves may be reduced for on-site usage and/or processing losses.


The ownership status of reserves may change due to the expiration of a production license or contract; when relevant to reserve assignment, such changes should be identified for each reserve classification.
Reserves may be attributed to either natural reservoir energy or improved recovery methods. Improved recovery includes all methods for supplementing natural reservoir energy to increase ultimate recovery from a reservoir. Such methods include (1) pressure maintenance, (2) cycling, (3) waterflooding, (4) thermal methods, (5) chemical flooding, and (6) the use of miscible and immiscible displacement fluids.


All reserve estimates involve some degree of uncertainty, depending chiefly on the amount and reliability of geologic and engineering data available at the time of the estimate and the interpretation of these data. The relative degree of uncertainty may be conveyed by placing reserves in one of two classifications: proved or unproved. Unproved reserves are less certain to be recovered than proved reserves and may be sub-classified as probable or possible to denote progressively increasing uncertainty.
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Proved Reserves

Proved reserves can be estimated with reasonable certainty to be recoverable under current economic conditions. Current economic conditions include prices and costs prevailing at the time of the estimate. Proved reserves may be developed or undeveloped.


In general, reserves are considered proved if commercial producibility of the reservoir is supported by actual production or formation tests. The term "proved" refers to the estimated volume of reserves and not just to the productivity of the well or reservoir. In certain instances, proved reserves may be assigned on the basis of electrical and other type logs and/or core analysis that indicate that the subject reservoir is hydrocarbon bearing and is analogous to reservoirs in the same area that are producing, or have demonstrated the ability to produce on a formation test.


The area of a reservoir considered proved includes (1) the area delineated by drilling and defined by fluid contacts, if any, and (2) the undrilled areas that can be reasonably judged as commercially productive on the basis of available geologic and engineering data. In the absence of data on fluid contacts, the lowest known structural occurrence. of hydrocarbons controls the proved limit unless otherwise indicated by definitive engineering or performance data.


Proved reserves must have facilities to process and transport those reserves to market that are operational at the time of the estimate, or there is a commitment or reasonable expectation to install such facilities in the future.


In general, proved, undeveloped reserves are assigned to undrilled locations that satisfy the following conditions: (1) the locations are direct offsets to wells that have indicated commercial production in the objective formation, (2) it is reasonable certain that the locations are within the known proved productive limits of the objective formation, (3) the locations conform to existing well spacing regulations, if any, and (4) it is reasonably certain that the locations will be developed. Reserves for other undrilled locations are classified as proved undeveloped only in those cases where interpretations of data from wells indicate that the objective formation is laterally continuous and contains commercially recoverable hydrocarbons at locations beyond direct offsets.


Reserves that can be produced through the application of established improved recovery methods are included in the proved classifications when (1) successful testing by a pilot project or favorable production or pressure response of an installed program in that reservoir, or one in the immediate area with similar rock and fluid properties, provides support for the engineering analysis on which the project or program is based and (2) it is reasonably certain the project will proceed.


Reserves to be recovered by improved recovery methods that have yet to be established through repeated commercially successful applications are included in the proved classification only (1) after a favorable production response from subject reservoir from either (a) a representative pilot or (b) an installed program, where the reponse provides support for the engineering analysis on which the project is based, and (2) it is reasonably certain the project will proceed.
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Unproved Reserves


Unproved reserves are based on geologic and/or engineering data similar to that used in estimates of proved reserves, but technical, contractual, economic, or regulatory uncertainties preclude such reserves being classified as proved. They may be estimated assuming future economic conditions different from those prevailing at the time of the estimate.


Estimates of unproved reserves may be made for internal planning or special evaluations, but are not routinely compiled.


Unproved reserves are not to be added to proved reserves because of different levels of uncertainty.


Unproved reserves may be divided into two subclassifications: probable and possible.
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Please i need API bulletin 14D ESTIMATION RESERVES

Post by ginoil »

hi adrian maybe do you have this material api bull 14d for upload
regards
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Post by adrian »

Probable Reserves

Probable reserves are less certain than proved reserves and can be estimated with a degree of certainty sufficient to indicate they are more likely to be recovered than not.


In general, probable reserves may include (1) reserves anticipated to be proved by normal stepout drilling where subsurface control is inadequate to classify these reserves as proved, (2) reserves in formations that appear to be productive based on log characteristics but that lack core data or definitive tests and which are not analogous to producing or proved reserves in the area, (3) incremental reserves attributable to in-fill drilling that otherwise could be classified as proved but closer statutory spacing had not been approved at the time of the estimate, (4) reserves attributable to an improved recovery method that has been established by repeated commercially successful applications when a project or pilot is planned but not in operation and rock, fluid, and reservoir characteristics appear favorable for commercial application, (5) reserves in an area of a formation that has been proved productive in other areas of the field but the subject area appears to be separated from the proved area by faulting and the geologic interpretation indicates that the subject area is structurally higher than the proved area, (6) reserves attributable to a successful workover, treatment, retreatment, change of equipment, or other mechanical procedure, where such procedure has not been proved successful in wells exhibiting similar behavior in analogous reservoirs, and (7) incremental reserves in a proved producing reservoir where an alternate interpretation of performance or volumetric data indicates significantly more reserves than can be classified as proved.
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