Deterministic reserves assessment methods
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Deterministic Reserves Assessment Methods. SPE/OERN Reserves ATW: Sharing the Vision John Lee Texas A&M University March 2011. Source of Presentation Materials. Draft version of new SPE/ AAPG/ WPC/ SPEE/ SEG (available free of charge on SPE Website) Guidelines for Application

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Deterministic Reserves Assessment Methods

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Deterministic reserves assessment methods

Deterministic Reserves Assessment Methods

SPE/OERN Reserves ATW:

Sharing the Vision

John Lee

Texas A&M University

March 2011


Source of presentation materials

Source of Presentation Materials

  • Draft version of new SPE/ AAPG/ WPC/ SPEE/ SEG (available free of charge on SPE Website)

    Guidelines for Application

    of the Petroleum

    Resources Management System

    Chapter 4


Uncertainty and assessment methods what when range of uncertainty

Uncertainty and Assessment Methods: What, When, Range of Uncertainty


Which specific method is most appropriate

Which Specific Method Is Most Appropriate?

Depends on

  • Type, quantity, quality of geoscience, engineering, and economic data available and required for technical and commercial analyses

  • Geologic complexity, recovery mechanism, state of development, degree of depletion


How should the deterministic procedure work

How Should the Deterministic Procedure Work?

  • Conduct ‘scenario analysis’ to bracket uncertainty and sensitivity to estimated values of parameters

  • Scenarios should represent low, best (most likely), high cases for original in-place and associated recoverable hydrocarbons

  • Depending on stage of maturity, scenarios represent PRMS categories of reserves (1P, 2P, 3P), contingent resources (1C, 2C, 3C), or prospective resources (low, best, high)


Volumetric and analogy methods

Volumetric and Analogy Methods

  • Volumetric method uses static data to obtain estimates of petroleum initially in place

  • Analogy method used to estimate recovery efficiencies

  • Procedures useful during exploration, discovery, post-discovery, appraisal, and initial development stages of E&P life cycle for any petroleum recovery project


Technical principles

Technical Principles

  • best determined from analog reservoir

    • In absence of rigorous analog, near-analog may be used

    • Numerical simulation (even lacking history match, if production data limited) also possibility

    • Analytical methods common in petroleum literature, but rapidly being replaced by simulation

    • Empirical correlations also available, but usually less satisfactory than simulation


Example illustrates principles and application

Example Illustrates Principles and Application

  • Example focuses on assessment of risk, uncertainty, classification, and categorization

  • Oil reservoir example: Various stages of maturity, over full life cycle


Example resource estimates in exploration appraisal initial development stages

Example: Resource Estimates in Exploration, Appraisal, Initial Development Stages

  • Example represents typical accumulation in mature petroleum basin with

    • Extremely large structures

    • Well-established regional reservoir continuity

    • Numerous adjacent analog development projects


Pre discovery structure net pay maps

Pre-Discovery Structure, Net Pay Maps

  • Prospect developed with seismic, geological studies

  • 2D seismic defined structural spill point, provided no indication of fluid contact locations

  • Analog reservoir suggested 30-33o API crude oil


Pre discovery resource estimates

Pre-Discovery Resource Estimates

  • High estimate: Based on regional analogs, assume structure full to spill point at 6,410 ft SS

  • Low estimate: Assume oil down to only 6,120 ft SS

  • Best estimate: Assume oil to intermediate depth of 6,265 ft SS

  • Uniform net-gross ratio of 0.7 assumed, and net-pay maps prepared


Prospective resource estimates

Prospective Resource Estimates


Post discovery well analysis

Post-Discovery-Well Analysis

  • Wildcat well encountered significant oil column sufficient to declare “discovery”

  • Geologic model updated (figure), net-gross pay ratio 0.75, net pay 89 ft

  • OWC not identified, so LKH in well penetration taken as OWC for low estimate (6,155 ft SS)


Post discovery well analysis1

Post-Discovery-Well Analysis

  • High estimate (3C): Assume structure full of oil to spill point

    • Alternative geological model indicates larger closure and higher recovery efficiency

  • Low estimate (1C): LKH defines 1C limit

  • Best estimate (2C): vertical limit set at 6,283 ft SS (intermediate depth)

  • Oil gravity found to be 32o API (PVT properties determined using this gravity)


Post discovery well reservoir maps

Post-Discovery-Well Reservoir Maps


Post discovery well volumetric analysis

Post-Discovery-Well Volumetric Analysis


Post discovery well analysis2

Post-Discovery-Well Analysis

  • Economic analysis encouraging, but chance of commerciality still estimated to be only 60%

    • Reclassification as Contingent Resources appropriate

  • Chance of gas above HKH not ruled out, but ignored in this analysis, awaiting detailed PVT and pressure gradient data

  • Owners unwilling to commit funds to a development project without additional data

    • Appraisal program designed for further evaluation


Appraisal delineation stage

Appraisal/Delineation Stage

  • Appraisal program implemented

    • Two additional wells drilled, tested, samples taken for PVT analysis

    • 3D seismic data acquired

  • New wells established lower LKH depth to 6,240 ft SS

  • PVT analysis established that oil is undersaturated, eliminated potential for gas cap


Appraisal delineation stage1

Appraisal/Delineation Stage

  • Logs, well tests, PVT analysis established

    • Initial pressure, reservoir temperature, average porosity, initial water saturation, reservoir permeability, oil gravity and viscosity, bubble-point pressure, Boi, Rsi

    • Stabilized rates averaging 3,500 STB/D

    • More definitive net/gross ratio distribution throughout reservoir


Appraisal delineation stage maps

Appraisal/Delineation-Stage Maps


Appraisal stage volumetric analysis

Appraisal-Stage Volumetric Analysis


Recovery project implemented resources classified as reserves

Recovery Project Implemented, Resources Classified as Reserves

  • Pressure maintained with peripheral water injection (well established in several analog reservoirs)

  • Project economics favorable

  • No market, legal or environmental contingencies identified

  • Management committed funds to project

  • Recoverable volume estimates refined, reclassified as reserves


Process continued through stages of greater reservoir maturity additional projects

Process Continued Through Stages of Greater Reservoir Maturity, Additional Projects

  • Continue to conduct ‘scenario analysis’ to bracket uncertainty and sensitivity to estimated values of parameters

  • Scenarios continue to represent low, best (most likely), high cases for original in-place and associated recoverable hydrocarbons

  • Later scenarios focus on continued refinement of reserves categories (1P,2P,3P)

  • Applications Guidelines (Chapter 4) highly recommended for additional reading


Deterministic reserves assessment methods1

Deterministic Reserves Assessment Methods

SPE/OERN Reserves ATW:

Sharing the Vision

John Lee

Texas A&M University

March 2011


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