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

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

    of the Petroleum

    Resources Management System

    Chapter 4


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


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?

  • 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 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

  • 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 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 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

  • 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

  • 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


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 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 Volumetric Analysis


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 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 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-Stage Volumetric Analysis


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

  • 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 Methods

SPE/OERN Reserves ATW:

Sharing the Vision

John Lee

Texas A&M University

March 2011


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