Session 1 log-analysis
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The document discusses key concepts in petrophysics including: - Petrophysics integrates formation evaluation data like logs and cores. - It involves analyzing logs to determine properties like porosity, water saturation, and clay content using equations. - A petrophysicist links subsurface data between geology and reservoir engineering to provide quantitative assessments of formations. - Their work involves complicated reservoirs and new technologies, but provides important outputs used across disciplines.
Session 1 log-analysis
- 2. 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 2 *Petrophysics is the study of rock properties and their interactions with fluids (gases, liquid hydrocarbons, and aqueous solutions) *The petrophysicist is the link between the subsurface disciplines *Petrophysics is the science that integrates many valuable data together to have quantitative formation evaluation based on conventional/advanced logs and core analyses *Log analysis vs. petrophysics
- 3. Log Analysis Different Inputs CertainOutputs GR Resistivity Porosity ɸ 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 3 𝑆#𝑉%&
- 5. What We Provide... 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 5
- 6. Is it Complicated?!! J 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 6 *A 24/7 job *Presence of hydrocarbon is your call *Wells/lithology could be very complicated *Tough to learn in most companies *Skill shortage in the industry *Too much to learn *What to start with? *Where/How to start? …........BUT, is it worth really?
- 7. A Shed of Light... 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 7 *Everyone takes the petrophysicist outputs to use *You are the link between the geologist and the RE *You learn how to manage, work under stress and how to provide only what is accepted *You manage the LWD and wireline operations *You are dealing with data no one literally see or use *You are dealing with new technology, that makes you always think *Your output is seen at all management levels
- 9. Log Example 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 9 This log is drawn by hand for presentation purposes only
- 10. What To Do (Simply)? 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 10 *Estimate clay volume *Calculate the porosity *Read the resistivity *Calculate water saturation REMEMBER!! The key for log interpretation is to understand how to read the log
- 11. How to Read the Log? 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 11 This log is drawn by hand for presentation purposes only
- 12. Clay Volume Calculation 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 12 *A simple equation using GR log is used to evaluate the clay volume *The neutron/density could be used to calculate the clay volume with the same equation *The softwares use different evaluation appraoches, a bit complicated, depending on the inputs used *Porosity tools or even resistivity could be used to evaluate the clay volume 𝑮𝑹 𝐥𝐨𝐠 , 𝑮𝑹 𝒄𝒍 𝑮𝑹 𝒔𝒉 ,𝑮𝑹 𝒄𝒍 =shV
- 13. Density Porosity Calculation 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 13 * The density log is the most robust porosity tool * The porosity is calculated using simple equation: ∅ 𝑫 = 𝝆 𝒎𝒂 − 𝝆𝒍𝒐𝒈 𝝆 𝒎𝒂 − 𝝆 𝒇𝒍 * Matrix density differs by lithology * L.ST: 2.71 g/cc * S.ST: 2.65 g/cc * Dol.: 2.847 g/cc * The 𝝆 𝒇𝒍 is the density of the fluid saturating the rock immediately surrounding the BH, (usually mud filtrate)....SLB * The tool is affected by washouts, rugose holes and high tension
- 14. Density Porosity Chart 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 14 27 p.u. *Determine the porosity from the density log value of 2.4 g/cc for a dolomite reservoir?
- 15. Sonic Porosity Calculation 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 15 * The sonic log is the reflecting primary porosity only * The porosity is calculated using simple equation: * Matrix density differs by lithology *S.ST: 55.5-51.3 µs/ft (18000-19500 ft/s) *L.ST: 47.6-43.5 µs/ft (21000-23000 ft/s) *Dol.: 43.5-38.5 µs/ft (23000-26000 ft/s) * The tool is used for seismic tie, CMT job evaluation and secondary porosity evaluation ∅< = ∆>?@A,∆>BC ∆>D?,∆>BC
- 16. Sonic Porosity Chart 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 16 10.5 p.u. *Determine the porosity from the sonic log value of 70 µs/ft for a sandstone reservoir? 34 p.u.
- 17. Calculating Total Porosity 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 17 * With 3 inputs, the porosity could be the average of them * For Gas Intervals ϕFGϕ<GϕH I = Tφ φT = FLMNOGHLMNO P
- 19. Porosity-Resistivity Pick 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 19 This log is drawn by hand for presentation purposes only
- 20. Water Resistivity (Rw) 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 20 * This is a key parameter in saturation calculation * Rw is evaluated through different methods: * Reversed Archie Method * Pickett Plot * Formation Water Salinity * The uncertainty in the Rw value affects the saturation profile near the contact dramatically This log is drawn by hand for presentation purposes only
- 21. Rw From Pickett Plot 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 21 *Pickett plot is very important tool to detect the water resistivity *It should be used as a confirmation for the reversed Archie method with more accuracy *The m value is the slope of the line *(m) value is crucial in carbonates *The core data is usually needed to vary (m) parameter, otherwise the default value is used
- 22. Salinity Value From Slb Chart 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 22 *Easily used to detect the Rw and salinity using the formation temperature *The salinity should not change across different locations/wells in the same structure *The Rw changes with temperature/depth *The formation salinity could vary significantly from formation to another
- 23. Calculating Water Saturation 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 23 *There are several models for Sw calculations *Two main reservoirs exist; clean and shaly reservoirs *The clean formations are evaluated with Archie equation *Shaly reservoirs use different models depend on the clay distribution *Schlumberger/Laminated sand-shale simplified model is one simple model to evaluate the shaly sands 1 𝑅a = ∅P 𝑆𝑤P 1 − 𝑉cde ∗ 𝑎𝑅𝑤 + 𝑉cde 𝑅%& 𝒂 ∗𝑹𝒘 Ф 𝒎 ∗ 𝑹𝒕 =n)W(S
- 24. Log Example 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 24 This log is drawn by hand for presentation purposes only
- 25. The Effective Porosity (Oil) 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 25 *In oil bearing reservoirs, the effective porosity curve is divided into three curves, the bulk volume of water (BVW), movable oil and residual oil. Residual Oil Movable Oil Bulk Volume Water 0.5 0effФ
- 26. The Effective Porosity (Gas) 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 26 *In gas bearing reservoirs, the effective porosity curve is divided into three curves, the bulk volume of water, the movable fluids and the gas. 0.5 0effФ Residual Gas Movable Hydrocarbon Bulk Volume Water
- 27. Sw-BVW Relationship 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 27 *Bulk Volume of Water is the volume of the water relative to the total bulk volume of the rock. *Water saturation is the amount of water in the pore spaces. Sw= BVW/ ϕ ϕ*wBVW = S
- 28. References 12/08/2016 Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 28 *Schlumberger Chartbook 2009 *Schlumberger Log interpretation principles and applications 1989