Gulf of Thailand Super Cube - Technical Challenges in the Reprocessing of 40 3D Seismic Surveys, 15000sq.km.
Authors: Phan Ying Peng , Lee Kok Moo , Soh Kim Kee , Sun Jason , Livesay George Allen , Hsiao Helmut , Jitharn Kantarakorn 
Published: May 2016

In early 2008, Chevron Thailand and partners contracted CGGVeritas to reprocess forty of their key 3D seismic surveys in the Pattani Basin, Gulf of Thailand, with a combined area of more than 15,000 sq.km. The 40 surveys had been acquired over a period of 26 years (1979 to 2005) with variable acquisition parameters, geometries and azimuths, which resulted in variable amplitude and frequency content and variable fold or sampling density. The benefit of the reprocessing is enormous, but the technical challenges are just as great. In this paper we present some of the technical challenges and solutions in the data processing work.

A) Detecting and correcting navigation errors in vintage data. Old surveys tend to have navigation errors. Some errors are not obvious until merging with adjacent surveys. We show how we detect the errors and correct them.

B) Data regularization. The data of the 40 surveys were loaded into common grid and offset slots for imaging. A challenge is to bridge any acquisition gaps caused by existing platforms at the time of acquisition. Using advanced interpolation technology, we filled in gaps as wide as 350m.

C) Offset-dependent matching of frequency bandwidth, amplitude, time and phase between surveys. We present a workflow that was tested and implemented successfully.

D) Fault imaging. We show how fault imaging was improved by incorporating anisotropy in migration.

Introduction

The Gulf of Thailand Super Cube project in the Pattani Basin was initiated and financed by Chevron Thailand, and carried out by CGGVeritas over a period of 3 years. The project area is shown in Figure 1. The 40 3D seismic surveys cover approximately 15,000 sq. km. Prior to the current project, the data had been processed individually or in small groups for use in interpreting individual field areas. The primary objective of the reprocessing was to produce superior seismic imaging by making use of more advanced processing technology, and by making use of neighbouring surveys as migration aperture input. Specifically, the reprocessing aimed to accurately define the principal faults, and to broaden bandwith for high resolution definition of the reservoirs and near water bottom reflectors for the assessment of drilling hazards. The reprocessing also brought about other benefits, which include: regional consistency with DHI or AVO assessment; continuous regional interpretation and data management; fewer seismic volumes to manage; reducing the number of (redundant) faults and horizons in the database; and conveniently working in multiple field areas without the need to switch seismic workstation projects during an interpretation session.

The 40 surveys were acquired over a time span of 26 years (1979 to 2005) with variable acquisition parameters, geometries and azimuths, which resulted in variable amplitude and frequency content and variable fold or sampling density. To merge them seamlessly requires great effort in spectral conditioning, time/phase matching, and AVO characteristics preservation.

In addition, for some vintage surveys, essential information such as source signature, accurate navigation and well preserved trace data could be missing or incomplete. The essential information had to be cross-examined and reconstructed to facilitate the reprocessing.