SEMINAR PETROLEUM GEOPHYSICAL EXPLORATION | Year:2013 | دوره:1 |Papers Count:6

FOURIER TRANSFORM PLAYS A KEY ROLE IN INTERPOLATION OF SEISMIC SECTIONS. FOURIER TRANSFORM ENABLES THE INTERPRETER TO EXTRACT THE FREQUENCY DATA WHICH IS NEEDED FOR REALIZING VARIOUS STRUCTURES. NON-STATIONARY SIGNALS BEHAVE EXTREMELY DIFFERENT THOUGH. WHEN WE ARE FACING A NON-STATIONARY SIGNAL, FINDING THE TIME-FREQUENCY MAP BECOMES A BIT COMPLICATED. THAT IS WHEN THE SHORT TIME FOURIER TRANSFORM (STFT) COMES IN HANDY. WE WILL DISTINGUISH THIS DIFFERENT BEHAVIOR OF NON-STATIONARY SIGNALS THROUGH THIS TEXT, AND WILL EXAMINE STFT IN PRACTICE.

ATTRIBUTE ANALYSIS IS CONSIDERED TO BE AN IMPORTANT STEP IN ANY SEISMIC RESERVOIR CHARACTERIZATION STUDY. DIVERSE ATTRIBUTES CAN BE INVESTIGATED IN ORDER TO OBTAIN A THOROUGH VIEW OVER THE CHARACTERISTICS OF DIFFERENT RESERVOIR LITHOFACIES. THE CHOICE OF DRILLING NEW LOCATIONS OR DEVELOPMENT PLANNING OF THE EXISTING WELLS RELIES CRITICALLY ON THE RESULTS ACQUIRED IN THIS STAGE.IN THIS STUDY, LAME PARAMETERS OF INCOMPRESSIBILITY AND RIGIDITY, POISSON IMPEDANCE AND POISSON DAMPENING FACTOR ARE ANALYZED TO COMPARE THEIR EFFECTIVENESS IN DISCRIMINATING LITHOFACIES AT THE ONLY WELL AVAILABLE IN THE STUDY AREA. THE RESULT OF POISSON IMPEDANCE AND LAME PARAMETERS CROSSPLOT ANALYSIS WERE CONSISTENT. MOREOVER, CROSSPLOT OF POISSON DAMPENING FACTOR RESPECT TO POISSON IMPEDANCE CAN BE USED TO DETERMINE THE QUALITY OF THE RESERVOIR.

THE OCCURRENCE OF A BOTTOM SIMULATING REFLECTOR (BSR) IN 2-D SEISMIC DATA OF MAKRAN ACCRETIONARY PRISM REVEALS THE PRESENCE OF HYDRATE RESOURCES ON OFFSHORE IRAN. ACCORDING TO THE GLOBAL DISTRIBUTION OF MARINE HYDRATES, THEY ARE WIDELY PRESENT IN DEEP SEA SEDIMENTS WHERE HIGH OPERATIONAL COSTS AND HAZARDS CAUSE A LACK OF WELL LOG INFORMATION. THEREFORE, DEVELOPING A TOOL TO QUANTIFY THE HYDRATE RESOURCES WITH SEISMIC DATA WOULD BE AN ULTIMATE GOAL FOR UNEXPLORED REGIONS. REFLECTIVITY TEMPLATES (RT) WERE INTRODUCED IN THIS STUDY FOR QUANTIFICATION OF THE HYDRATE AND FREE GAS NEAR THE BSR. THESE RTS ARE INTUITIVE CROSSPLOTS OF P- AND S-IMPEDANCE CONTRASTS ACROSS THE BSR. THEY ARE THEORETICALLY CALCULATED BASED ON THE EFFECTIVE MEDIUM THEORY (EMT) FOR DIFFERENT HYDRATE DISTRIBUTION MODES WITH SOME ASSUMPTIONS ABOUT POROSITY AND MINERALOGICAL COMPOSITION OF UNCONSOLIDATED SEDIMENTS. THIS TECHNIQUE WILL SUGGEST THE POSSIBILITY OF USING THE AVO ANALYSIS OF THE BSR FOR A QUANTITATIVE INTERPRETATION WHEN WELL LOG DATA IS NOT AVAILABLE. BY SUPERIMPOSING THE AVO-DERIVED P- AND S-IMPEDANCE CONTRASTS ON THESE RTS, THE SATURATIONS OF THE HYDRATE AND FREE GAS COULD BE ESTIMATED. THE RESULTS OF USING THIS APPROACH FOR A 2-D MARINE PSTM DATA SHOWED THAT 4 TO 28% OF THE GAS HYDRATE AND 1 TO 2% OF THE FREE GAS ARE ACCUMULATED NEAR THE THRUSTED-RIDGE AND THRUSTED-FOOTWALL TYPES OF BSRS IN IRAN DEEP SEA SEDIMENTS.

THE METHOD OF AMPLITUDE VARIATION WITH ANGLE (AVA) INVERSION WAS APPLIED TO ESTIMATE HYDRATE AND GAS SATURATIONS ALONG A BOTTOM SIMULATING REFLECTOR (BSR) AT THE MAKRAN ACCRETIONARY PRISM, IRAN. THREE AVA APPROXIMATIONS WERE USED AND THEIR CORRESPONDING AVA ATTRIBUTES WERE COMPARED TO EACH OTHER. VS/VP VALUES ARE USUALLY UNKNOWN FOR UNEXPLORED REGIONS AND HERE A SIMULATED ANNEALING APPROACH WAS TAKEN TO DERIVE THE VS/VP IN A NUMBER OF LOCATIONS. THESE VALUES WERE THEN INTERPOLATED TO GET AN ESTIMATION OF VS/VP FOR OTHER LOCATIONS.QUANTIFICATION OF HYDRATE AND GAS SATURATIONS WAS BASED ON A CORRELATION BETWEEN THE AVA INVERTED ATTRIBUTES AND THE ROCK PHYSICS DERIVED ATTRIBUTES (RPDA). CORRESPONDING SATURATIONS OF THE NEAREST RPDA TO A PAIR OF AVA INVERTED ATTRIBUTES WERE CONSIDERED AS THE HYDRATE AND GAS SATURATION FOR THAT SPECIFIC LOCATION. THE QUANTIFICATION ASSESSMENT INDICATED 11%, 14% AND 15% HYDRATE SATURATIONS IN THE VICINITY OF THE BSR FOR LOCATIONS WITH LOW, INTERMEDIATE AND HIGH POST-STACKED AMPLITUDE, RESPECTIVELY. THE SATURATION OF THE FREE GAS WAS ALSO ESTIMATED AS < 1%, 2% AND 3% WITH THE SAME ORDER AS ABOVE, RESPECTIVELY.

PROCESSING OF SEISMIC DATA IS AN INDISPENSABLE STEP IN EXPLORATION SEISMOLOGY. THE PURPOSE OF SEISMIC PROCESSING IS TO MANIPULATE ACQUIRED DATA INTO AN IMAGE OR SET OF IMAGES OF THE SUBSURFACE GEOLOGY. PROCESSING CONSISTS OF APPLYING A SEQUENCE OF ROUTINES ON A COMPUTER GUIDED BY A GEOPHYSICAL PROCESSING SPECIALIST. OBTAINING A PRECISE IMAGE OF SUBSURFACE IS NECESSARY FOR ACCURATE INTERPRETATION OF SUBSURFACE SECTIONS AND LEADS TO EXPLORING THE OIL TRAPS SUCH AS SYNCLINES, SALT DOMES, FAULTS AND STRATIGRAPHIC FEATURES. IN THIS ARTICLE WE HAVE FULFILLED THE PRINCIPLE STEPS OF SEISMIC DATA PROCESSING SUCH AS DENOISING, NMO CORRECTION, VELOCITY ANALYSIS, STACKING AND MIGRATION RESPECTIVELY ON A SYNTHETIC 3D SEISMIC DATA AND FINALLY OBTAINED AN SYNCLINE THAT CAN BE THE POTENTIAL OF HYDROCARBON ACCUMULATION.

SEISMIC DATA ARE BAND-LIMITED, THEREFORE ONE CAN USE ONLY A PARTIAL SET OF FREQUENCY COEFFICIENTS IN THE RANGE OF REFLECTIONS BAND, WHERE THE SIGNAL-TO-NOISE RATIO IS HIGH AND SPATIAL ALIASING IS LOW, TO RECONSTRUCT THE ORIGINAL WAVE FIELD. FURTHERMORE, LOW-FREQUENCY CHARACTERISTICS OF THE COHERENT GROUND ROLLS ALLOWS DIRECT ELIMINATION OF THEM DURING RECONSTRUCTION BY DISREGARDING THE CORRESPONDING FREQUENCY COEFFICIENTS (USUALLY BELLOW 10 HZ) VIA A FREQUENCY MASK. IN THIS PAPER, A NON-LINEAR ALGORITHM IS PROPOSED WHICH ADDRESSES SOME CHALLENGES OF SPATIAL SAMPLING, RECONSTRUCTION, AND DENOISING IN SEISMIC EXPLORATION. NUMERICAL EXPERIMENTS FROM BOTH SIMULATED AND REAL FIELD DATA ARE INCLUDED TO ILLUSTRATE THE EFFECTIVENESS OF THE PRESENTED METHOD.