Zulfadhli Bin Mohd ZakiResearch Profile : Seismic illumination study has becomes a new approach by the industry to improve the seismic data quality in recent years. The complexity of geology has resulting in improper illumination on the reflector surface, thus giving rise to the problem of poor data quality on a certain area with low illumination. Given the fact that seismic illumination study can be conducted in small amount of time with relatively cheaper cost than acquiring 3D seismic survey, it is an new industry approach to solve the poor data quality problem in complex geology. The ability to 'guest' the seismic data quality of the survey area before and during the acquisition thus give an advantage to acquisition survey be conducted economically and effectively by changing the array geometry of source and receiver to give the best illumination on the whole area or seismic infill for the local area with low quality image. The objective of this study is to conduct a seismic illumination study using a local area (propose target area is zone of poor image quality resulting from shallow gas cloud) solely on focal beam method to a multiply scattered wave. Conventional seismic processing eliminated the multiple as geophysicist regards the multiples as 'noise'. However, if multiple are consider as scattered wave which later recorded by the detector which reflected on a surface reflector, it increase the illumination of seismic wave especially in the zone which are poorly illuminated (i.e shallow gas cloud) by the primary wave. The idea is to use the multiple as the illumination from below of the target zone. Using the double focusing beam, it does not required to change the migration algorithm but rearranging source and receiver array distribution at the designed target area with minimal cost possible.

Abstract : The conventional acquistion design in using CMP threated as equal as CRP (Common Reflecting Point) has given considerably unstatisfied illumination on the target subsurface. In area of complex geology, the seismic illumination at the taget depth are not well distributed and in some cases, it is not sufficient which later resulting in the poor data quality. The focus of this studies is to do an illumination studies using the focal beam analysis. It is required to simulate wave propagation from the receiver to the target area and back to receiver in seperate manners. The WRW model intoduced by Berkhout is appropriate model to well explained the focusing method. The WRW model formulate seismic reflection as the multiplication of matrices. It corperate anngle dependence reflcetivity as the replacement for ray tracing method. The analysis of in term offset angle dependence illumination (AVP) and resolution function will be reviewed to obtain the best acquistion configuration for iteratively improve the illlumination of the target area. The area complex area such as gas cloud area give trouble to intepreter in determining the structure below the affected area. The low velocity zone relative to surrounding are the reason the illumination under the shallow gas area are affected. Nevertherless, the multiple which are recorded previously are considered 'noise', does illumination the lower part of the seismic. The computation of focal beam which incorperated the multiples as will increase the illumination for the target area. Thus, this study might be able for fault under the shallow gas cloud to be image.

(a) The WRW model concpets. (b) convolution matrix operator. Taken from Doulgeris, Mahdad, & Blacquire (2009)

ObjectiveConduct seismic illumination studies using focal beam method by assimilating WRW model concept as well as analysis of AVP and resolution function.Incorperate the multiple in the forward seismic wave modelling and design an acqusition configuration. The acquistion desidn mustberealisticApply foward modelling to the real data and analyze the illumination result.

Methodology