SEMINAR PETROLEUM GEOPHYSICAL EXPLORATION | Year:2015 | دوره:2 |Papers Count:6

HIGH DEMAND OF THE INDUSTRIAL WORLD TO HYDROCARBON MAKES THE PETROLEUM INDUSTRY TO SEARCH FOR NEW RESERVES IN MORE COMPLICATED GEOLOGICAL AREAS. TO REACH THIS AIM, IT IS CRUCIAL TO LOOK FOR CUTTING-EDGE TECHNOLOGIES IN EXPLORATION GEOPHYSICS. IN THIS PAPER, WE MAINLY ATTEMPT TO BRIEFLY REVIEW SOME OF NEW ADVANCES IN EXPLORATION SEISMIC ESPECIALLY IN IMAGING DOMAIN. IT SHOWS HOW THE FULL WAVEFORM INVERSION SCHEME CAN PROVIDE US THE HIGHER RESOLUTION PHYSICAL MODEL COMPARED TO CONVENTIONAL TRAVEL-TIME TOMOGRAPHY. IF ADDITIONAL SOURCES OF PRIOR INFORMATION (ADDITION TO SEISMIC DATA) EXIST, IT WOULD BE REALLY VALUABLE TO USE THEM AS A CONSTRAINT FOR SEISMIC INVERSION SCHEME, ESPECIALLY IN TIME-LAPSE APPLICATION WHERE SEVERAL PRIOR DATA ARE AVAILABLE. ANOTHER ADVANCE IN GEOPHYSICS IS RELATED TO TIME-LAPSE IMAGING WHERE IT IS POSSIBLE TO ESTIMATE QUANTITATIVELY THE RESERVOIR PARAMETER CHANGES DURING PRODUCTION PHASE. AT THE END, CHOOSING A PROPER COMPUTATIONAL DOMAIN FOR ANALYZING THE SEISMIC DATA IS IMPORTANT. PROBABLY FITTING THE DATA IN ANOTHER SPACE WOULD BE EASIER AND LEAD TO MORE ROBUST RESULTS COMPARED TO THE ORIGINAL DOMAIN.

VELOCITY ANALYSIS IS PROBABLY THE MOST CRITICAL STAGE OF PROCESSING FLOW SINCE IT IS AN INITIAL INTERPRETATION OF THE DATA. HOWEVER, IT IS STILL ONE OF THE MOST TIME CONSUMING PARTS OF SEISMIC PROCESSING. CONVENTIONAL VELOCITY SCAN METHOD IS PERFORMED BY MEASURING ENERGY ALONG HYPERBOLIC PATHS FOR A RANGE OF VELOCITIES. FOR A TWO DIMENSIONAL DATA IT RUNS IN COMPLEXITY O (N3) WHICH WILL BE COMPUTATIONALLY EXPENSIVE FOR DATA OF DIMENSION N WHEN N IS LARGE. HERE WE PROVIDE THE BUTTERFLY ALGORITHM AS AN ALTERNATIVE METHOD WHICH WILL LEAD TO SPEED UP OF SEVERAL ORDERS OF MAGNITUDE, O (N2LOGN).

DETERMINATION OF DIFFERENT STRUCTURAL AND STRATIGRAPHIC FEATURES PRIOR TO ANY COSTLY IMPLEMENTATION IS A GREAT AID IN THE OIL AND GAS EXPLORATIONS AND DEVELOPMENTS THAT COULD BE EFFICIENTLY ACHIEVED BY 3D SEISMIC ATTRIBUTE ANALYSIS. IN THIS STUDY POST STACK SEISMIC INVERSION IS USED IN CONJUNCTION WITH DIFFERENT SEISMIC VOLUME ATTRIBUTES SUCH AS INSTANTANEOUS PHASE, SWEETNESS, CURVATURE, SEMBLANCE, SPECTRAL DECOMPOSITION, ETC., TO DETECT CHANNEL FEATURES IN ADDITION TO EVALUATE THEIR INFILL LITHOLOGY VARIATION IN ONE OF THE IRANIAN OFFSHORE HYDROCARBON FIELDS. AFTER EXTRACTING SEISMIC VOLUME ATTRIBUTES, SEISMIC FACIES ANALYSIS IS PERFORMED TO RECOGNIZE MEANINGFUL VARIABILITY WITHIN THE 3D SEISMIC DATA IN ORDER TO HIGHLIGHT GEOLOGIC FEATURES, GENERALLY HIDDEN WITHIN THE REDUNDANT SEISMIC NOISE, AND RENDER THE RESULTS AS A SEISMIC FACIES MAP. FOR THIS REASON, PRINCIPAL COMPONENT ANALYSIS (PCA) IS USED TO PERFORM DIMENSION REDUCTION OF A MULTIVARIATE DATASET BY COMPRESSING THE BULK OF THE VARIANCES IN THE SEISMIC DATA INTO AS FEW VECTOR COMPONENTS AS POSSIBLE. GENERATED RESULTS REVEALED A MAJOR, VERY DISCREET CHANNEL FEATURE CUTTING EAST-WEST ACROSS THE MIDDLE PART OF THE FIELD IN THE ILAM FORMATION.ANOTHER CHANNEL FEATURE IS ALSO DETECTED TO THE SOUTH OF THE FIELD IN THE SARVAK FORMATION BASED ON INVERSION RESULTS. CONSEQUENTLY, INFILL LITHOLOGY VARIATIONS OF DETECTED CHANNELS WERE EVALUATED BY SEISMIC INVERSION RESULTS VARYING FROM DENSE (HIGH ACOUSTIC IMPEDANCE VALUES) TO POROUS (LOW ACOUSTIC IMPEDANCE VALUES) IN DIFFERENT INTERVALS. THE RESULTS OF THIS STUDY IN CONJUNCTION WITH GEOLOGICAL STUDIES COULD BE USED TO CHOOSE NEW WELL LOCATIONS WITH MORE CONFIDENCE.

SEISMIC DATA FREQUENCY FILTERING IS ONE OF THE IMPORTANT STEP IN SEISMIC STUDIES. THE AIM OF FILTERING IS TO CLARIFY SOME FEATURES OF SUBSURFACE AREA WHICH CAN’T BE SEEN IN THE AVAILABLE SEISMIC DATA. GEOPHYSICIST USUALLY DESIGN FILTERS BASED ON THEIR EXPERIENCE, THEY MANUALLY PICK SOME FREQUENCIES FROM AMPLITUDE SPECTRUM OF DATA WITHOUT ANY MATHEMATICAL REASON. HERE WE USE A LEAST SQUARE SCENES IN SPECTRAL RECOMPOSITION CONTEXT TO EXTRACT MOST IMPORTANT PEAK FREQUENCIES IN ORDER TO DESIGN FILTER. RESULT SHOW THAT THE PROPOSED METHOD WORK BETTER THAN ORMSBY FILTERING, A COMMONLY USED FILTERING METHOD BY GEOPHYSICIST.

ACOUSTIC IMPEDANCE (AI) INVERSION ALLOWS MAPPING THE SEISMIC REFLECTION DATA TO LITHOLOGY AND HENCE IT PLAYS AN IMPORTANT ROLE IN RESERVOIR CHARACTERIZATION AND INTERPRETATION OF POST-STACK SEISMIC DATA. THE AI IS OBTAINABLE FROM THE INVERSION OF THE EARTH REFLECTIVITY SERIES. EFFICIENT DECONVOLUTION METHODS HAVE BEEN DEVELOPED FOR RECOVERING THE REFLECTIVITY SERIES FROMBANDLIMITED POST-STACK DATA. HOWEVER, THE EXISTING AI INVERSION METHODS OFTEN ARE UNSTABLE.SPECIFICALLY, THEY FAIL TO GENERATE AN ACCEPTABLE IMPEDANCE MODEL WHEN DEALING WITH COMPLEX STRUCTURES BECAUSE OF PROCESSING THE DATA IN A SINGLE CHANNEL SCHEME. CALCULATION OF THE AI FROM THE REFLECTIVITY, WHEN CONSIDERING THE SPATIAL CORRELATION OF THE IMPEDANCE PARAMETERS, DEMANDS SOLUTION OF A CONSTRAINED NONLINEAR INVERSE PROBLEM.IN THIS PAPER, I PROPOSE AN EFFICIENT ALGORITHM FOR SOLVING THE NON-LINEAR IMPEDANCE PROBLEM IN MULTICHANNEL FORM WITH THE TOTAL-VARIATION (TV) CONSTRAINT IN ORDER TO RECOVER IMPEDANCE MAPS WITH BLOCKY STRUCTURES. THIS ALLOWS STABILIZING THE IMPEDANCE MODELS EVEN IN VERY COMPLEX STRUCTURES. NUMERICAL TESTS USING TWO- AND THREE-DIMENSIONAL FIELD DATA CONFIRMED THAT THE PROPOSED ALGORITHM GENERATES MORE ACCURATE WITH HIGHER RESOLUTION IMPEDANCE MODELS COMPARED WITH THE CONVENTIONAL METHODS WHICH ARE CURRENTLY USED IN THE INDUSTRY.

IN THIS PAPER, AT FIRST, WE PRESENT METHODS TO PRODUCE HIGH RESOLUTIONSHORT-TIME FOURIER TRANSFORMBY COMPUTING OPTIMAL INSTANTANEOUS WINDOW-LENGTH. SECOND, WE USE THE GENERATED TIME-FREQUENCY MAP FOR EXTRACTIONINSTANTANEOUS TRAVELTIME ATTRIBUTE FOR AUTOMATIC PICKING OF TRAVELTIME OF SEISMIC EVENTS. NUMERICAL EXAMINATIONS OVER A THREE-COMPONENT SYNTHETIC SIGNAL IDENTIFY HIGH PERFORMANCE OF THE PROPOSED TIME-FREQUENCY ANALYSIS METHOD. ALSO, TO SHOW CAPABILITY OF THE METHOD FOR AUTOMATIC TRAVELTIME PICKING, WE APPLIED IT ON A RAW FILED DATA.