PETROPHYSICS ROCKLOGSEISMIC CALIBRATION John T Kulha Petrophysical Consultant

PETROPHYSICS: ROCK/LOG/SEISMIC CALIBRATION John T. Kulha Petrophysical Consultant July 2016

Petrophysical Evaluation 2

Petrophysics: data acquisition • Acquire digital log files in LAS format – – lithology: spontaneous potential, gamma ray resistivity: normal, lateral, induction porosity: density, neutron, compressional and shear acoustic others: caliper, microlog, cased-hole gamma ray/neutron, LWD/MWD, images, NMR • Review paper copy log data – verification of digital data – additions to existing digital data base (microlog, etc) • Acquire paper/digital copy of hydrocarbon logs – ROP, TG and CG curves; description of shows (fluorescence, cut, odor, etc); lithology • Rock data from multiple sources; petrophysical measurments 3

Petrophysics: data preparation • Build continuous digital file of all log curves in measured depth – LAS files (LIS, DLIS, ASCII) – digitize or scan to infill any missing data • Enter log header and log run information – mud parameters (weight, resistivities) – maximum temperature • Enter paleontological, geological correlation markers, perforations, test and core intervals – annotations of test results, production, core description, etc • Enter core data into digital log file – porosity, permeability, grain density, fluid saturations, etc 4

Petrophysics: data preparation • Perform selected edits of invalid data – “hand” edits (between runs, casing points, obvious bad data) – edits using similar response curves (conductivity) – edits using synthetic curves (acoustic or density) • Depth merge log curves to resistivity – porosity (neutron, bulk density, sonic) – lithology (gamma ray, spontaneous potential) – depth correlation between neutron and bulk density! • Enter directional information and perform TVD calculations (if applicable) 5

Petrophysics: data preparation • Perform environmental corrections and conversions – – – borehole and mud weight to gamma ray matrix conversion to neutron bulk density/density porosity shift spontaneous potential to a constant shale baseline resistivity invasion • Normalization of key log curves – neutron, bulk density and acoustic, gamma ray – only if reasonable data coverage and distribution exists – consistent “normalization” lithology interval in all wells – review quality of resistivity (“strange profiles”) – consistency in regional shales and/or other lithologies 6

Petrophysics: model development • Determine shale volume for clastic and carbonate reservoirs usingle curve and x-plot indicators – – – SP, gamma ray, neutron, bulk density, resistivity neutron-density, neutron-sonic and sonic-density crossplots average value for final shale volume minimum value for final shale volume calibrate to X-ray diffraction or other core-derived clay measurements – compare final composite shale volume curve to individual components – gamma ray and/or neutron-bulk density better in carbonates – calibrate with geological model • Use to calculate “effective” from total porosity 7

Petrophysics: model development • Determine total porosity – matrix porosity (macro- and micro-porosity) – secondary porosity: fracture, vugular – correct to effective porosity • Multiple porosity tools – – compensated neutron log and bulk density (PHIND) compensated neutron log and acoustic (PHINS) compare PHIND with PHINS compare acoustic and PHIND for secondary porosity • Single or two porosity tools – compensated neutron log and the bulk density (PHIND) – compensated neutron log and acoustic (PHINS) – acoustic or density (PHIS, PHID) 8

Petrophysics: model development • Parameter selection (Rw, m, n, CEC, Qv, Rsh) • Formation water resistivity (Rw) – – produced water: wireline, DST’s, intial tests or production offset wells water salinity catalogues analysis of spontaneous potential, need mud filtrate resistivity value (Rmf) • Rw and cementation exponent (m): Pickett crossplot – total porosity versus resistivity (log-log crossplot) – apply in wet reservoirs; hydrocarbons won’t define Rw 9

Petrophysics: model development • Special core analysis for cementation (m) and saturation (n) exponents – rock catalogues with analogous rock types – empirical relationships – estimated from cuttings • Clay electrical properties for cation-exchange capacity water saturation model – clay type, amount and mode of distribution – analytical measurements – empirical relationships • Log-derived shale properties for shale volume water saturation model – clay type and mode of distribution – average log values in adjacent or internal shales 10

Petrophysics: model development • Water saturation calculation (Archie model) – – resistivity from deepest investigating curve (invasion? ) total porosity formation water resistivity, Rw cementation, m, and saturation, n, exponents • Water saturation calculation (shale volume models) – – – Modified Simandoux, Indonesian, others resistivity from deepest investigating curve (invasion? ) effective porosity (shale values RHOB, NPHI, DT) shale volume, porosity and resistivity formation water resistivity, Rw cementation, m, and saturation, n, exponents 11

Petrophysics: model development • Water saturation calculation (cation-exchange capacity models) – – – – – Waxman-Smits, Dual Water (rigorous or simplified) resistivity from deepest investigating curve (invasion? ) total porosity cation exchange capacity equivalent conductance specific clay area bound water resistivity formation water resistivity cementation, m (m*), and saturation, n (n*), exponents shale volume and porosity 12

Petrophysics: model development • Pay distribution and reservoir properties are defined by cutoffs of key log curves – – porosity water saturation shale volume other curves, as needed (hydrocarbon pore volume, perm) • Cutoffs should be calibrated – – producing intervals in wells intervals that produce water analogue data consistent with permeability estimation • Reservoir property summation used in geological model, simulation, reserves and completion design 13

Petrophysics: example evaluation 14

Rock/Log/Seismic Calibration 15

Rock/Log/Seismic Calibration-1 • Relationships between “rocks/logs/seismic” – rocks/logs/seismic must be calibrated to provide a complimentary and realistic geoscience and engineering evaluation – petrophysics and “petro-geophysics” • Rocks and logs – logs calibrated to rock type/reservoir quality – standard petrophysical relationships – porosity, water saturation, reservoir quality, permeability, pay • Rocks and seismic – seismic calibrated to rock type/reservoir quality – elastic variables – velocity, bulk density, acoustic impedance • Logs and seismics – – seismic “calibrated” to corrected logs (rock type/reservoir quality) synthetic elastic logs lithology and fluid models synthetic seismograms 16

Rock/Log/Seismic Calibration-2 ROCKS PETROPHYSICAL ELASTIC VARIABLES RELATIONSHIPS LOGS VARIABLES SYNTHESIZED SYNTHETIC ELASTIC LOGS SEISMOGRAMS SEISMIC SYNTHESIZED MODEL ROCK/FLUID TIME/DEPTH SEISMIC LOG TRANSFORM DISTRIBUTION SIGNATURE AVO CALIBRATION 17

Rock/Log/Seismic Calibration-3 • Recorded acoustic and bulk density logs – inaccurate: miscalibration, erroneous tool response, service company problems – incomplete: intervals not logged, data not recorded, data lost – unavailable: logs not run, data lost, old wells (pre-sonic and bulk density) • Synthetic acoustic and bulk density logs – generated from resistivity/conductivity (primary independent variable) – generated from shale volume (secondary independent variable) – generated as a function of depth, rock type, correlation interval, geologic age, pressure regime (tertiary independent variables) – applied a common regression algorithm to a maximum number of wells within a project area • Problems resolved by synthetic logs – – – borehole rugosity and erroneous measurements effects of borehole alteration due to drilling fluid reaction and stress relief different service companies’ tools and associated tool response variations tool miscalibration; wrong log scales (paper logs) incomplete or unavailable logs 18

Rock/Log/Seismic Calibration-4 • Synthetic logs for in-situ conditions – – effects of lithology and rock type change wet reservoir response hydrocarbon response identify intervals of questionable measured data • Synthetic logs for modeled conditions – changes in lithology or reservoir quality – hydrocarbon fluid substitution – variations in reservoir quality and fluid content • Synthetic seismograms from synthetic logs – consistent character within a project area – provide usable well/seismic tie – provide synthetics where log data in not available or unusable 19

Rock/Log/Seismic Calibration-5 • Correlate intervals of similar rock properties – – rock properties related to wireline log responses guided by regional depositional model and environments guided by regional seismic correlation with preliminary log/seismic tie incorporate mudlog lithology and/or independent cuttings descriptions – “overlook” intervals of questionable or missing log data • Create shale volume curve – – lithology related wireline logs gamma ray, spontaneous potential, neutron/density, resistivity defined by either reservoir scale or seismic scale flexible to accommodate changes in lithology • Build calibration data set – – select intervals of acceptable measured log data “experience” driven and supplemented with other discipline input representative of all various independent variables inclusive of multiple well data sets 20

Rock/Log/Seismic Calibration-6 • Perform multivariable regression and calculate synthetic logs – – – – shale volume (VSH) log resistivity (RT) or conductivity (COND) log Other log curves, NPHI, PE, mudlog curves(? ) depth, geologic age, depositional environment, pressure regime regression coefficients, A 1, A 2, A 3, A 4 RHOB=A 1+A 2*(VSH)+A 3*(LOG (RT), COND)+A 4*(DEPT) DT=A 1+A 2*(LF, VSH)+A 3*(LOG (RT), COND)+A 4*(DEPT) may simplify to only two variables • Compare synthetic logs with calibration data set – modify calibration intervals, other independent variables – repeat process until correlation with measured data or tie to seismic is acceptable • Perform fluid substitution or calibrate directly – calibrate directly to in-situ fluid conditions – calculate wet reservoir condition and then substitute hydrocarbons – selected intervals from representative wells 21

Example well: 4 intervals 2950’- 4000’ 4400’- 5400’ T 1: SP-blue; GR-black, VSH-red T 2: RD-red; RM-green T 3: RHOB-black; RHOB-ED, red; CALI-green 6100’- 7600’ 8100’- 9750’ T 4: DT-black; DT-ED-red Yellow shading indicates amount of error between measured and synthetic (corrected) log curve 22