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

Petrophysical Evaluation

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

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

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)

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

Petrophysics: model development Determine shale volume for clastic and carbonate reservoirs using single 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

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) acoustic or density (PHIS, PHID)

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

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 Log-derived shale properties for shale volume water saturation model clay type and mode of distribution average log values in adjacent or internal shales

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 effective porosity (shale values RHOB, NPHI, DT) shale volume, porosity and resistivity

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

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

Petrophysics: example evaluation

Rock/Log/Seismic Calibration

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

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

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

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

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

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, A1, A2, A3, A4 RHOB=A1+A2*(VSH)+A3*(LOG (RT), COND)+A4*(DEPT) DT=A1+A2*(LF, VSH)+A3*(LOG (RT), COND)+A4*(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

Example well: 4 intervals 2950’- 4000’ 4400’- 5400’ T1: SP-blue; GR-black, VSH-red T2: RD-red; RM-green T3: RHOB-black; RHOB-ED, red; CALI-green T4: DT-black; DT-ED-red Yellow shading indicates amount of error between measured and synthetic (corrected) log curve 6100’- 7600’ 8100’- 9750’