PETROPHYSICAL EVALUATION CORE COPYRIGHT. Petrophysical Evaluation Approach and Shaly Sands Evaluation. By the end of this lesson, you will be able to:

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1 PETROPHYSICAL EVALUATION CORE Petrophysical Evaluation Approach and Shaly Sands Evaluation LEARNING OBJECTIVES By the end of this lesson, you will be able to: Discuss how to approach a petrophysical evaluation including data sources and required parameters Explain why, at a minimum, we need a porosity log and a resistivity log to calculate water saturation Tell about the difference in traditional log analysis and statistical log analysis 1

2 FURTHER STEPS IN EVALUATION Introduce Petrophysical Evaluation Process Flow Re-visit net terminology Discuss porosity and statistical models Introduce saturation models for shaly sands Influence of shale on logs and production Shaly sand evaluation: models based on V shale and R shale Saturation models based on electrical double layer theory Objective: To make you aware of some petrophysical evaluation considerations beyond quick-look. INTERPRETATION DETAIL VERSUS APPLICATION? Level of Detail One point from one zone in a well Petrophysicist A few zones in one works closely well with geologist and reservoir An entire well engineer to Many wells in tailor approach. a field Application Pick top, marker bed, casing, test or core point Completion/testing decisions Reserves, well to well correlations Field study, mapping, ϕ, OOIP, etc. 2

3 DATA GATHERING HOW MUCH? RECONNOITERING Start with overall view Use a 1" 2" per 100' log scales (1/500 or 1/1000 scale for log depths in meters) Sources of Data LWD Mudlogs Wireline logs Core analyses Wireline testing Produced fluid analysis Test results Look for trends Visit with other disciplines. Does the story make sense? Quick-look key areas Shales versus sands Porous zones Permeable zones 3

4 MODEL SELECTION CONSIDERATIONS For clean formations For shaly sandstones Use Archie equations including thin beds, and clay mineral effects: Use resistivity and ϕ readings DETERMINING CALCULATION PARAMETERS Bare minimum Sometimes useful Lithology parameters For multi-mineral, mixed lithologies m, n, R w R mf including carbonates and evaporites Use statistical models Shale parameters Preliminary cutoffs for net pay ρ ma, Dt ma, etc. GR sh, fn sh, r sh, R sh, etc. Ø, S w, V sh, B vw, etc. 4

5 CALCULATIONS Computer analysis packages (petrophysical software) Spreadsheets for petrophysical evaluations and pay summaries Quick-look methods: Cross-plots, R wa, etc Service company statistical analysis Provide petrophysical answer products Understand the process and inputs Scientific calculators and nomograms PETROPHYSICAL EVALUATIONS: PROCESS FLOW (1) Petrophysics is all about integration of data and its interpretation! 5

6 PETROPHYSICAL EVALUATIONS: PROCESS FLOW (2) INTERPRETATION REMINDERS In the case of a field study, be ready to iterate. Log Used Objective Parameters Required SP, GR Density, Neutron, Sonic, P e Laterlog Induction Find reservoir rocks Ø Find Porosity & Lithology S w Find Water Saturation Neutron Matrix Setting ma, t, b t ma, t f, t SFL or MSFL Density, Neutron, S x0 Find S x0 hy Determine hydrocarbon type h Find pay thickness OIP Find Oil in Place N Recoverable volumes R t, R w, Ø a, m & n R x0, R mf, Ø a, m & n Ø N, Ø D Sw maximum Ø minimum H, Ø, S w OIP, Area Recovery Factor o or g 6

7 A FEW MORE WORDS ON POROSITY Due to presence of mixed mineral lithologies, porosity and lithology often determined with Statistical Log Analysis software. Traditional Log Analysis Statistical Log Analysis LEARNING OBJECTIVES You should are now now: able to: Discuss how to approach a petrophysical evaluation including data sources and required parameters Explain why, at a minimum, we need a porosity log and a resistivity log to calculate water saturation Tell about the difference in traditional log analysis and statistical log analysis 7