4C Mahogony Data Processing and Imaging by LSMF Method Jianhua Yu and Yue Wang

Outline Motivation and Objective LSMF Method Examples Graben Model Mahogany Field Data Summary

Outline Motivation and Objective LSMF Method Examples Graben Model Mahogany Field Data Summary

Geological Objectives Image Complex Structure Detect Gas Reservoir Over Salt

Problems Strong Guided Waves P-SV Conversion at Reflector ? How to Get “Pure” P-P and P-SV Strong Guided Waves

Problems for F-K Use only wave moveout Strong guided waves Near offset distortion

P-P and P-SV Waves Source P-P P-SV Point Scatterer

Least Squares Migration Filtering Moveout Particle Motion Direction Time + offset Separation

Separate P-P & P-S Suppress Guide Waves Improve Migration Image Objective Separate P-P & P-S Suppress Guide Waves Improve Migration Image

Outline Motivation and Objective LSMF Method Examples Graben Model Mahogany Field Data Summary

LSMF with Moveout m p = L m = [ Lp Lps ] m m [L L] L d m = moveout PS -1 T = m ps PS P

LSMF with Moveout+2-Comp. Particle Motion P PS q (cos q , sin q ) (sin q , -cos q ) u = u + u p ps v = v + v total 2-component particle motion data p = L m = [ Lp Lps ] m p ps Scalar moveout m u = [ cos(q)Lp sin(q) Lps ] p ps Vector moveout + particle motion v = [ sin(q)Lp -cos(q) Lps ]

LSMF Method = > Dpp + Dp-s Lpp mpp P-P wave Time Lp-s mp-s P-S wave Observed data Dp-s Lp-s mp-s Lpp mpp Reflectivty Modeling Operator P-P wave Time P-S wave Offset

LSMF Filtering Step dpp = Lppmpp dp-s = Lp-smp-s P-P wave Time Time P-S wave Offset Time P-P wave Offset Time

LSMF Method Operators are constructed based on moveout and particle-motion direction The migration operators are the transposes of the modeling operators

Outline Motivation and Objective LSMF Method Examples Graben Model Mahogany Field Data Summary

Examples Graben Model Mahogony Field Data

Graben Velocity Model 5000 X (m) Depth (m) 3000 V1=2000 m/s X (m) V1=2000 m/s V2=2700 m/s V3=3800 m/s Depth (m) V4=4000 m/s V5=4500 m/s 3000

FD Synthetic Data P-P P-S P-S P-P Horizontal Component Offset (m) Offset (m) 5000 5000 P-P P-S Time (s) P-S P-P 1.4 Horizontal Component Vertical Component

LSMF Separation P-P P-S Horizontal Component Vertical Component Offset (m) 5000 Offset (m) 5000 P-P P-S Time (s) 1.4 Horizontal Component Vertical Component

F-K Filtering Separation Offset (m) 5000 Offset (m) 5000 P-S P-P Time (s) P-S P-P 1.4 Horizontal Component Vertical Component

Test Results Indicate: LSMF works well for separating P-P and P-SV LSMF is superior to F-K filtering

Examples Graben Model Mahogony Field Data

Acquisition Survey Shot Line OBC 9 km 29 km

Main Processing Flow Geometry assignment, datuming and so on Trace edit, noise elimination, dual-sensor summation Amplitude Recovery Static correction, (F-K filtering), multiple suppression LSMF, velocity analysis Migration Output

Raw CSG Hydrophone component Vertical component Offset(m) Offset(m) -750 725 -750 725 Continuous events Continuous events Time (s) 4 Hydrophone component Vertical component

Raw CSG Radial component Transverse component Offset(m) Offset(m) -750 725 -750 725 Wormy events Wormy events Time (s) 4 Radial component Transverse component

Raw CRG Hydrophone component Vertical component X (m) X (m) Time (s) 3750 3750 Continuous events Continuous events Time (s) 4 Hydrophone component Vertical component

Raw CRG Radial component Transverse component X (m) X (m) Time (s) 3750 3750 Continuous events Continuous events Time (s) 4 Radial component Transverse component

Rough Estimate of Static Shift Source Receiver 12 p s Receiver static Static shift (ms) Source Receiver p s Shot static -4 100 Station Number

Data Analysis Indicates: The Shear static shifts exist These shifts mainly come from receivers and one-way Shear path from deeper reflector P-S waves originate from reflectors

CRG1 Data before Using LSMF Guided wave and P-S Time (s) 4 CRG1 (Vertical component)

CRG1 Data after Using F-K Filtering Unwanted waves remain Time (s) 4 CRG1 (Vertical component)

CRG1 Data after Using LSMF Less Noise remains Time (s) 4 CRG1 (Vertical component)

Prestack Migration Image With F-K Separation Midpoint (Km) 4.6 c Time (s) 3.5

Prestack Migration Image With LSMF Separation Midpoint (Km) 4.6 c Time (s) 3.5

A Zoom View of Box A Time (s) Midpoint (Km) Midpoint (Km) FK+Mig. 0.6 1.4 0.6 1.4 2.0 Time (s) 3.2 FK+Mig. LSMF+Mig.

A Zoom View of Box C Time (s) Midpoint (Km) Midpoint (Km) FK+Mig. 3.4 4.6 3.4 4.6 0.2 Time (s) 0.8 FK+Mig. LSMF+Mig.

Outline Motivation and Objective LSMF Method Examples Graben Model Mahogany Field Data Xwell Data Summary

SSP Synthetic

Xwell

Outline Motivation and Objective LSMF Method Examples Graben Model Mahogany Field Data Summary

Summary and improves the migration image P-SV waves in Mahogony data originate from the deep reflectors LSMF gives better separation results and improves the migration image

Summary LSMF can eliminate unwanted noise, such as guided waves LSMF has negative impact on the fidelity of data to some extent

Summary Future Research: Multiple Elimination Prestack Depth Migration Converted Wave Imaging

Acknowledgement We are grateful to the 1999 sponsors of the UTAM consortium for financial support