An Innovative Approach to 3D Survey Design to Meet Exploration and Development Objectives: An OBC Case History from Offshore Malaysia
Authors: Chandola Sandeep Kumar , Ghazali Faizan Akasyah , Law Chung Teck , Ghazali Ahmad Riza , El Kady Nabil , Sharma Sachin Kumar , Abdul Rahman Mohd. Ramziemran , Nafisah Sarah , Kumar Subodh 
Published: May 2016

PETRONAS conducted a 3D-2C Ocean Bottom Cable (OBC) survey in the year 2012 offshore Malaysia, to appraise a recent hydrocarbon discovery and assist the field development plan and production enhancement initiatives. The legacy 3D towed streamer data acquired in 1984 suffered from poor imaging of the faults and significant navigation errors.

In order to meet the stringent seismic imaging requirement and considering the possibility of the new 3D-OBC data being used as the baseline for future 4D surveys, an innovative 3D survey design modification was implemented during data acquisition, based on the review of initial data. Staggered-grid source-receiver 3D survey design was used to improve the spatial sampling from 25m x 12.5m in the exploration area, to 12.5m x 12.5m in the development area, without augmenting the available equipment. In addition, denser source lines were used in the development area to improve the near-offset distribution and the fold coverage. Denser spatial and near offset sampling were considered crucial for optimal sampling of the seismic wave-field (both signal and coherent noise), a robust SRME solution and an overall superior seismic imaging. Stringent quality control measures ensured good quality of data throughout the survey. In-field processing showed significant improvement in seismic resolution and fault imaging in the development area, indicating the success of the staggered-grid 3D survey design.

Data processing was performed through anisotropic pre stack time migration and successfully addressed various challenges encountered in data acquisition and processing.

The new 3D-OBC data displays higher resolution as compared to the legacy streamer data with crisper fault definitions, improved reflection continuity a robust Class II AVO response at the reservoir level and better low frequency imaging of the deeper targets.

Innovative 3D survey design has enabled to produce a high quality 3D-OBC dataset meeting both exploration and development objectives in a cost-effective manner.

Introduction

PETRONAS conducted a 3D Ocean Bottom Cable (OBC) survey in offshore Malaysia in the year 2012. The 3D-OBC survey was originally planned to appraise a recent hydrocarbon discovery and to cover the data gap in shallow water area. The survey area extended into the adjoining producing field (Fig.1). The legacy seismic data over the field, acquired in 1984, suffered from poor seismic imaging due to short streamer length (1500m) and significant navigation errors adversely affecting the fault imaging, considered critical for reserve calculations. Two of the drilled wells missed one reservoir sand because of lateral difference in fault positioning with an estimate of around 100,000 bbls of recoverable hydrocarbons. The regional 3D towed streamer data acquired in 2002 excluded the development area due to coralreefs, existing platforms and surface facilities. Therefore, the development team decided to farm into the exploration 3D-OBC data acquisition campaign after it was awarded, with the following objectives: