Impact of Seismic Acquisition and Processing Techniques in Challenging Subsurface Imaging; Block G11/48, Gulf of Thailand

Abstract

The availability of high quality seismic data is of critical importance in trying to unravel the complexities of subsurface geology. This paper illustrates how proper selection of seismic acquisition parameters and data processing techniques can successfully overcome geological difficulties and minimize uncertainties when exploring for hydrocarbons in the northern part of Block G11/48, Gulf of Thailand, without compromising safety and cost efficiency. Fluvial and fluvio-deltaic sediments of early to mid Miocene age in low relief faulted structural traps constitute the most common hydrocarbon habitat in the area of investigation. Amplitude support in identifying potential targets is also proven by nearby discoveries. To fully evaluate the exploration potential of this area, a 3D seismic acquisition campaign was successfully carried out using a high-end seismic vessel and without HSSE incidents. The Nong Nuch dataset was acquired using a 10 deep-flat towed 5.1 km streamer configuration with triple sources to increase cross-line resolution and reduce operational time. This long streamer length relative to the target depth provides necessary information to Full Waveform Inversion and Q-tomography in order to correct push-down effects in broadband anisotropic Pre-stack Depth migration. The dataset also helps to obtain high accuracy velocity model, de-multiple and quantitative interpretation. This acquisition and processing approach significantly improved the ability to image thin reservoirs and correct push-down effects and energy absorption due to gas clouds or unconsolidated sea floor channels. The large streamer spread and deep tow did not create any major problems throughout the acquisition. The implementation of broadband acquisition and leading edge processing techniques resulted in good signal to noise ratio as well as high vertical and horizontal resolution with minimal acquisition footprint. In addition, long offset data acquisition contributes to successful attenuation of short and long period multiples. Channel-like features and fault plane reflections are very clearly imaged in the dataset, helping to better understand of the depositional environment and structural setting of the area. Severe push-down and abnormal amplitude absorption effects were significantly corrected and compensated by building a high resolution, Full Waveform Inversion (FWI) derived velocity model as well as application of reflection tomography and Q-tomography techniques. Thus, definition of potential traps beneath gas clouds has significantly improved.