HR: 16:35h
AN: NS54A-02    [Abstracts]
TI: EXPLORATION FOR GAS HYDRATES IN DEEPWATER NORTHERN GULF OF MEXICO
AU: Dai, J
EM: jdai@slb.com
AF: Schlumberger, 10001 Richmond Avenue, Houston, tx 77042, United States
AU: * Dutta, N C
EM: NDutta@houston.oilfield.slb.com
AF: Schlumberger, 10001 Richmond Avenue, Houston, tx 77042, United States
AB: In recent years, gas hydrates have drawn significant attention from scientific community worldwide due to their potential as an alternative energy resource and as a possible agent for both shallow drilling hazard, and global climate change. Gas hydrates have been known to exist extensively in shallow sediments from permafrost regions to deepwater oceans. The vast amount of naturally occurring hydrates is a large potential for an energy resource. While the world demand for fossil fuel is ever increasing and the supply is dwindling, it is imperative to assess whether gas hydrates can provide energy to fill the void. As a principle technology in hydrocarbon exploration, the seismic reflection method becomes a natural choice for exploring gas hydrates. In this paper, we present a petroleum systems approach to exploration of gas hydrates in which seismic data analysis and interpretation techniques play key roles. We developed an integrated, seismic-based, five-step workflow to delineate and quantify gas hydrates in the deepwater Gulf of Mexico (GoM). The method integrated geological interpretation, seismic processing and inversion, and rock physics modeling to ascertain the existence and quantify the naturally occurring gas hydrates. We applied the methodology on two blocks in the northern GoM and estimated hydrate concentration in the pore space, both at selected locations in 1D and a cube in 3D. Due to lack of hard data (well control) for the shallow seismic data, our predictions used analogue models based on geologic interpretation, seismic inversion, and the basic principles of rock physics. Based on model predictions, several wells were drilled recently on two blocks (KC 195 and ATV 14) in the GoM. We collected wireline, LWD/MWD, and core data. The post-drill analysis confirmed our methodology and validated the exploration mode. In this paper, we also present and discuss the drilling results and compare our pre-drill predictions with the drilling data and the lessons learned. The comparison indicates that our pre-drill seismic predictions for gas hydrate saturations are in agreement with the log-based estimates (resistivity and sonic), as well as core data, especially when the hydrate concentrations are high. However, some uncertainties do exist regarding the current seismic detection method. These are mostly due to lack of constraints on shallow rock models and seismic inversion during the pre-drill phase. Despite these uncertainties, our seismic-based methodology did provide valuable pre-drill information for selecting potential drill sites and to further characterize gas hydrate-bearing sediments. This technique could be used elsewhere, both onshore and offshore.
DE: 0935 Seismic methods (3025, 7294)
DE: 3025 Marine seismics (0935, 7294)
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly