classification of reserves

8/9/2019 Classification of Reserves

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Hypothetical reserves assessed from indirectresults of geological, geophysical and drillingdata.

D1 and D2 based on degree of reliability ofavailable data.



Commercial reserves are assessed on the basisof:

1. Subsurface geological and reservoir data.

These reserves are classified into a,b,c1,c2 andza balance.



Conditions:

Detailed limits are established.

All the wells are drilled as per technological schemes

and production already started. Complete geometry of reservoir and reservoir

mechanics are known. All B.H. samples have beenanalyzed by P.V.T cell. Well productivity, dry

mechanism, composition and other details areknown.



Conditions:

Field is delineated commercial flow of oil and gashave been established.

Data is sufficient to implement a technologicalscheme.



Conditions: Structure has been delineated by seismic/ and geological data. Commercial flow established. DSD/ RFT data is available. Wells have been tested.

Complete studies of B.H. and production testing have been carried out.(Probable Reserves) The boundary condition estimation of C1 category reserves should be as

follows:a) Fluid parameters are established by conventional testing in one well. The pool

limits will be defined by1. Fluid contacts are seen2. Base of Origin in case no fluid contacts are seen or3. By the lowest depth of perforation.

b) In case the testing of the well is carried out by open hole DST, or in the case thereservoir fluid properties and calculating parameters are taken on the basis ofadjacent pools, the limit of estimation will be restricted to double spacing ofproducing wells in a near by area.

c) The limit of estimation will be restricted to one well spacing wherecommerciability is judged from the geological analysis.



The C2 reserves are estimatedA. Unexplored part of the field adjoining the areas having

higher category of reserves.Or

B. Where one well has been drilled or the electrologindications are positive. The pool limits will be definedeither by lowest depth up to which positive indication ofelectrologs are observed or lowest closed contourswhere there are no indications of fluid contacts on logs.

Or

C. Or where presence of hydrocarbon has been establishedby geological evaluation with partial fulfillment ofcriteria for estimation of C1 category reserves.

No recoverable reserves are quoted for C2 reserves.



These reserves cannot be developed profitablyat the present time owing to the limited size ofthe reserves, poor quality of oil gas, poor

productivity of the wells, difficult condition ofexploitation. These reserves can be conservedas quality 2 objects for commercial exploitationin the future with improvement in productiontechnology, logistics, geo-politicalenvironment. These reserves will require asubstantially higher price or a major costreducing advance in technology to becommercially producible.



Classification of reserves have been modified in 1986 and1990 by ONGC.

In western countries, the reserves of petroleum or theamount that can be produced at a profit from known fields,using known techniques in known time.

In India, the reserves are defined as estimates of oil/gas inplace which can be realistically apprised with existingknowledge of parameters such as structures, stratigraphy,depth, size, fluid properties, and reservoir mechanics. Therecoverable reserves are that part of in place reserves whichcan be economically exploited with existing technology.

With the opening of oil sector to multinationals, need wasfelt to change the categorization of reserves to US securitiesand exchange commission and SPE classification, which isby and large accepted by most of the countries.



Initially, in place hydrocarbons or the volumesof crude oil, condensed, natural gas, naturalgas liquids and associated substances

anticipated to be present in knownaccumulations at a given time.

The initial in place hydrocarbons are classifiedas proved and unproved.

The unproved will be further sub-classified asprobable and possible.



Proved OIIP and GIIP It is estimated volume/quantity, as of specified data,

which on evaluation of available geophysical,geological and engineering data demonstrates withreasonable certainty to be present in the reservoir.

The OIIP and GIIP are considered proven if theconditions:

Structure/trap has been delineated with fair degree ofcertainty.

Sustained flow has been established by wells located in

different parts of the structure. Reservoir geometry petrophysical and fluid parameters

and reservoir mechanism are well defined.



Probable OIIP and GIIP Probable OIIP and GIIP is less certain than proved OIIP or GIIP

because data required may not be complete or its analysis mynot be conclusive. Probable OIIP or GIIP includes Where structure/trap has been delineated by geophysical and

geological data with a fair degree of certainty.

Sustained flow has been established in at least one well.

The area will be defined by

a) Fluid contacts

b) Base of pay zone/reservoir in case no contacts are seen.

c) Lowermost zone of perforation

Possible OIIIP and GIIP Possible OIIP and GIIP is also estimated on the same basis as

proved or probable categories with less data or less conclusiveinterpretation than required for placement of this volume inprobably category.



Proved Reserves Reservoirs that are estimated to be commercially recoverable with a high degree of

certainty from known accumulations, under existing economic conditions by

established operating practices and under government regulations. Proved reserves must have facilities process and transport to market that are

optional at that time or reasonable expectation to install such facilities in the future.The reserves are considered proved if commercial production has been establishedby actual production or successful testing. Volumetrically thus structure, arealextent, volume and characteristics of the reservoir are well defined by a reasonableinterpretation of adequate well control and by known continuity of hydrocarbonsaturated material about known fluid contacts or about the lowest known structureof occurrence of hydrocarbons.

The proved reserves are further subclassified in Developed Undeveloped

Developed Reserves Developed reserves are expected to be recovered from existing wells. Improved

recovery reserves are considered only after the necessary equipment has beeninstalled or when the costs to do so are relatively low.

Undeveloped Reserves

Undeveloped reserves are expected to be recovered from New wells/completions in undrilled acreage or Where a relatively large expenditure is required to install production or

transportation facilities for primary or improved recovery projects.



Unproved Reserves

Unproved Reserves are based ongeologic and/or engineering datasimilar to the proved category but

various uncertainty precludes suchreserves being classified as proved.

Unproved Reserves may bedivided into two sub-classifications

Probable and Possible



Probable Reserves

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

Probable reserves may include the following conditions:

Incremental reserves attributable to infill drilling but statutoryspacing has not been approved by the time of estimates.

Reserves attributable to an improved recovery method that hasbeen established by depleted commercially successfulapplications when a project or a pilot is planned but not inoperation and rock, fluid and reservoir characteristics appears

favorable for commercial production. Incremental reserves in proved producing reservoirs where an

alternate interpretation of performance or volumetric dataindicate significantly more reserves than can be classified asproved.



Possible Reserves

Possible reserves are less certain than probable reserves andcan be estimated with a low degree of certainty, insufficientto indicate whether they are most likely to be recovered than

not. Volumes estimated to be recoverable from proved and/or

probable OIIP or GIIP of a reservoir.

Incremental reserves attributable to infill drilling that aresubject to technical uncertainty.

Reserves attributable in improved recovery method when aproject or pilot is planned but not in operation and rock,fluid and reservoir characteristics are such that areasonable doubt exists that a project will be commercial.

classification of reserves

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