All about Reserves Estimation

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

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All about Reserves Estimation

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Dear All,

I hope to enjoy my new thread and hope to find it helpful.

This topic is dedicated to Reserve Estimation and procedure to calculate it...
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Reserves Estimation: Introduction

The term "reserves" means different things to different people. To the banker, reserves are the amount of capital retained to meet probable future demands. To the oil and gas operator, reserves are volumes of crude oil, natural gas, and associated products that can be recovered profitably in the future from subsurface reservoirs.
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Reasons for Reserve Estimates


Estimates of oil and gas reserves are required for different purposes by different segments of the industry and at different stages in the life of a particular oil and gas property. Segments of the industry concerned with oil and gas reserves include
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Depending on the scope of their operation, operators of oil and gas properties require reserve estimates at various stages of exploration, development, and production. Of concern are
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Uncertainties in Reserve Estimates

Estimates of oil and gas reserves are inherently uncertain. The extent and nature of commercially recoverable hydrocarbons from the subsurface cannot be determined with a high degree of precision. Recovery from subsurface reservoirs depends largely on the heterogeneities of the reservoir rock and the type of reservoir drive mechanism. Neither of these factors can be determined with a reasonable degree of certainty until after an accumulation has been developed and placed on production. Desorcy (1979) has discussed the source and probable magnitude of many of the errors associated with estimates of oil and gas reserves.
In addition to these physical uncertainties, there are commercial uncertainties. In the long run, oil and gas recovery is controlled by
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Typically, these costs are incurred over a period of many years, with significant expenditures frequently being required a year or more before any income is realized.


The commercial environment
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Geologic Complexity


The degree of geologic complexity in a group of properties may vary widely. At one extreme, the properties may be in an area of low structural relief, little or no faulting, no unconformities, and oil and gas reservoirs in the same general type of depositional unit (e.g., the lower Tuscaloosa (Cretaceous) trend in the southeastern USA). At the other extreme, the properties may be in an area of considerable structural relief, extensive faulting, numerous unconformities, and multiple depositional units (e.g., the North Sea).

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Maturity


We can describe the maturity of an oil and gas property in terms of three stages of development and production:
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Thanx adrian..

I'm following,,,
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Quality and Quantity of Data


The minimum data necessary to estimate reserves with a reasonable degree of confidence vary widely from one property to the next and depend, in part, on the geology and maturity of the property. For a property that is monitored from its discovery and produces by primary reservoir drive mechanisms, acquisition of most or all of the following data is recommended:
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In reservoirs with improved recovery projects, this list should be expanded to include surveillance of monthly injected volumes and pressures from each injection well. Data requirements for improved recovery projects tend to be method and project specific. Talash (1988) has discussed data requirements for waterflood projects. The National Petroleum Council (1984) has published an extensive bibliography of papers on improved recovery methods which can provide insight into data requirements for such methods.
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Operating Environment


The operating environment of an oil and gas property is one of the major factors controlling the costs of developing and operating the property. These costs, and the market price of the production, have a direct impact on the minimal size of a commercially exploitable accumulation and, thus, whether any portion of the accumulation may be classified as "reserves."

In the North Sea, for example, an accumulation containing 30 million barrels of oil in place was considered marginal (Home et al. 1988). It was a candidate for commercial exploitation only because it was near an existing production platform and could be produced from satellite facilities. In contrast, in West Texas
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Definitions and Classifications of Petroleum Fluids and Reserves


Definitions of Petroleum Fluids

The following definitions are adopted, in part, from Martinez et al. (1987)
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Petroleum

Petroleum is a general term that applies to all naturally occurring mixtures that consist predominantly of hydrocarbons. Petroleum includes natural gas, crude oil, and natural bitumen. (The reserve estimation techniques discussed here do not consider natural bitumen.)

Crude Oil

Crude oil is the portion of petroleum that exists in the liquid phase in natural underground reservoirs and remains liquid at atmospheric conditions of temperature and pressure. Crude oil may contain small amounts of nonhydrocarbons produced with the liquids. Crude oil has a viscosity equal to or less than 10,000 millipascal seconds (centipoise) at original reservoir temperature and atmospheric pressure, on a gas-free basis. (This is approximately the viscosity of 8
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Natural Gas

Natural gas is the portion of petroleum that exists either in the gaseous phase, or in solution in crude oil, in natural underground reservoirs, and is gaseous at atmospheric pressure and temperature. Natural gas may include amounts of nonhydrocarbons.

Natural gas may be subclassified as associated or nonassociated gas. Associated natural gas is found in contact with, or dissolved in, crude oil in a natural underground reservoir. Nonassociated natural gas is found in a natural underground reservoir that does not contain crude oil. (Many gas reservoirs classified as "nonassociated" contain oil columns that are too thin to support a statutory oilwell completion.)
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