But these are what we really measure with logs..

Transcription

1 The role of the petrophysicist in reservoir characterization and the analysis of reservoir performance. What do we bring to the table? What do we want to take home? Bob Cluff The Discovery Group Inc. consulting geoscientists and petrophysicists Denver, Colorado Presentation at SPE Applied Technology Workshop, Key West, Florida, 8 Feb 2007

2 The big 3 we all want to know. Porosity Permeability Fluid saturation

3 But these are what we really measure with logs.. Natural earth potentials (spontaneous potential) between beds Electrical conductivity Natural gamma ray radiation Neutron slowing down length Thermal neutron capture cross secton Speed of sound Electron density from gamma ray scattering Gamma ray photoelectric absorption Nuclear magnetic resonance relaxation time just about any property of matter you can think of.

4 Role of the petrophysicist Is to take the physical properties we can measure downhole,then turn them into something useful. That is, the reservoir properties of interest.

5 Two faces of Petrophysics Measurement science What physical properties can be measured that might be useful/interesting? Physics of the measurement Engineering how to make the measurement in a dark, noisy, dirty downhole enviroment Converting the raw measurements to something closer to the property of interest

6 Electron density Gamma rays are emitted by radioisotope source. GR s are scattered by the electron clouds surrounding the nearby atoms (Compton scattering). GR s detected at 1, 2 or 3 nearby detectors are attenuated, with the reduction directly proportional to the density of electrons between the source and the detectors.

7 Logging sonde US Patent 3,321,625 May, 1967

8 Electron density vs. bulk density 6 5 pyrite bulk density (g/c3) coal limestone quartz dolomite 1 0 water electron density (rhob x 2Z/A)

9 Spine and ribs plot

10 The second face. Interpretation science Interpreting physical measurements in terms of rock properties of interest determine porosity from bulk density determine hydrocarbon saturation from electrical conductivity and porosity Interpretation model development Integration of petrophysical properties with engineering and geology

11 Example: bulk density interpretation The raw tool count rates have been converted to bulk density and corrected for mudcake thickness by the logging service company, but we want to know the porosity of the formation, not the density.

12 Bulk density-density porosity plot Schlumberger, 2005

13 Porosity computation PhiD = (RhoMa( RhoB)/(RhoMa RhoFl) Where: RhoMa = the matrix density RhoB = measured bulk density RhoFl = fluid density Problem for the interpretation petrophysicist is: What is the matrix density? Rocks are rarely pure end member minerals- they are usually mixtures so the matrix density will not be a constant value. What is the fluid density? Water, oil, gas, or a combination thereof? At formation conditions. Do we need to know saturation to solve for porosity??

14 Density porosity solution Density Is this a change in matrix density (lithology) or a change in fluids?? LESA 6.1, Digital Formation, Inc. File: LA-LIME.LAS Well Name: LOUISIANA LIMESTONE GRCORR Plot: C-DN-S46.PLT Plot Name: Density vs. Comp. Neutron 0 (S-1991, [N/A] 300p.46) Gross Interval: 7950 to 8170 by 1 F Ranges: Time: 05:59 PM Date: Sat, Feb 03, 2007 Schlumberger Chartbook (1991) p.46 Kspar 0 Sulfur Salt Plagioclase Sandstone 20 Limestone Anhydrite Dolomite OCNL Illite 40 Kaolinite GRCORR 0 [N/A] Chlorite Density 1.95 G/C Neutron 0.45 V/V Sonic US/F Pe 40 0 [N/A] 20 Density 1.95 G/C Neutron 0.45 V/V Sonic US/F Pe 40 0 [N/A] 20

15 Sandstone Limestone Dolomite Log example Schlumberger Chartbook (1991) p.38 Salt Sulfur K-spar Plagioclase 0 Anhydrite LESA 6.1, Digital Formation, Inc. File: _Daniels 1.las Well Name: DANIELS Plot: Interactive Shale Point - English.plt Plot Name: Density vs. Pe (S-1991, p. 64) Gross Interval: to by 0.5 F Ranges: Time: 06:13 PM Date: Sat, Feb 03, 2007 Illite Shale Point Kaolinite Neutron Schlumberger Chartbook (1991) p.44 0 Limestone Limestone Sandstone Sandstone 0 Dolomite Chlorite Time Average Sylvite Field Observation Gypsum Salt Trona Polyhalite Sulfer Sonic Transit Time (us/ft) Density Density Anhydrite Shale Point Salt 15 Sandstone Anhydrite Limestone Limestone Dolomite Schlumberger Chartbook (1991) p.42 Time Average Field Observation Shale Point Schlumberger Chartbook (1991) p Salt Sandstone Dolomite Montmorillonite Limestone Kaolinite Illite Shale Point Neutron Pe [N/A] Chlorite Sonic Transit Time (us/ft) Density 0 10 Anhydrite 0 Density in Shale = Neutron in Shale = Dt in Shale = 65 Pe in Shale = 3.5

16 So what is it we do? We integrate the observed tool response with Our geologic understanding of the formation of interest. Core and ditch cutting samples Mud log observations All the other log measurements that respond to lithology and porosity to obtain a consistent & logical interpretation

17 Biggest challenges facing petrophysics in this decade #1 is people, people, people! Look around you. We re not getting younger. Largest potential pool of petrophysical talent will be the people retiring from big companies. Retirees don t t want to work in a traditional office or cubicle, 8-5, 8 commuting environment Expect to see micro-consultancies pop up in odd places like Key West, Maui, Tuscon,, etc. We are working towards a virtual office concept where our employees can be scattered around the world, we ll provide the infrastructure

18 Challenges #2 is also people! Frankly, we don t t work together very well. Still an inherent tension in this industry between engineers and geoscientists. Cross-disciplinary training and even understanding of what the other people are doing remains weak. There are HUGE gains to be made in how we interact and work together.

19 Challenges #3 is permeability Perm is the farthest property of interest from what we can measure with wireline or LWD tools Dynamic properties are difficult to determine from static measurements Inherently vector quantity when we mostly take scalar, omni-directional measurments Perm itself is poorly understood at the rock level We don t t do too bad a job in sandstone reservoirs, but carbonates and tight formations are tough

20 Challenges #4 is the evaluation of unconventional reservoirs Todays seals, tomorrows reservoirs We re producing TCF s of gas from rocks that are tighter than the seals over most offshore fields Tight gas sands are difficult, but gas shales are a whole different ballgame

21 What do we bring to the party? Understanding of the underlying measurements & physics we re putting the physics back into Petrophysics Geologic expertise and our understanding of the behavior of earth materials Ability to work with diverse data collected over many years, bringing it together into as coherent a package as possible

22 What do we need back from you? Ground truth. Integration of the static data with the dynamic data. Feedback to improve our models and representations if they are not providing a plausible reservoir description. Help us sort out non-unique answers.