博士 / 國立中央大學 / 地球物理研究所 / 100 / Bottom simulating reflectors (BSRs) observed on seismic sections are often considered as indicators for the existence of free gas, delineating the base of the gas hydrate stability zone. Abundant BSRs seen on seismic sections acquired off the SW coast of Taiwan indicate the likely and prevalent existence of gas hydrates in the study area. Four major occurrences of BSR types, including ridge type, basin type, submarine-canyon type, and continental-slope type, are recognized on the basis of the relationship of BSRs to topographic and structural features.
On the basis of tectonic and sedimentary features, BSR spatial distribution, inferred gas sources, migration pathways of gas-bearing fluids, geological and geochemical anomalies, characteristics of reservoir for hydrate occurrences, trap structures, this study established 3 large-scale gas-hydrate system models and 6 gas hydrate-bearing provinces in both the accretionary wedge and the South China Sea continental slope. The mechanisms of gas hydrate occurrence of the high-potential prospects situated in gas-bearing provinces can be categorized into 8 major gas hydrate play types. The results show that a prospect, which has higher potential for gas hydrate occurrence, features the combination of mixed gas sources, multiple migration conduits, large area of high-porosity reservoir, and well-developed trap structure. For examples, the frontal fold of accretionary wedge (R1.1 structure), ancient submarine fan (KP-12), buried mud diapir (KP-14) in the lower reach of the Kaoping canyon among others, are three prospects inferred to host a large amount of gas hydrates.
There is a widespread occurrence of BSRs beneath the frontal fold (R1.1 structure) suggesting a promising gas hydrate existence. A seismic flat spot and a few push-down reflectors below BSR found lying underneath the anticlinal axis with bathymetric four-way dip closure also reveal abundant free gas accumulation beneath the structure. The free gas may derive from deep-seated gas-bearing fluids which migrate upward along multiple fault zones or permeable beds in addition to shallow-seated biogenic gas. The northward migrating of paleo-Penghu canyons driven by tectonic uplift of frontal fold have six stages of canyon/channel incisions marked by distinct channel infills. The multiple paleo-canyon infills seen along the frontal fold and above BSRs may provide thick porous sands to host a large amount of gas hydrate beneath the frontal fold.
This study employed volumetric method to calculate the gas-hydrate resource for each prospect in the study area. The approach of Monte Carlo simulation was used to evaluate the probabilistic distributions for each parameter and gas hydrate resource. The parameters involved in the calculation are gas hydrate-bearing area, gross thickness, net-to-gross ratio, porosity, gas-hydrate pore saturation, volume ratio, and cage occupancy. The results show that the total resource of gas hydrates in the study area is 2.7 trillion cubic meters taking the computed value at 50% probability of occurrence. The prospect with the largest resource potential is the frontal fold of accretionary wedge, amounting to 21 tcf (~5.9×1011 cubic meters) of natural gas. The results indicate that future deep-sea drilling is essential for exploring and confirming the gas-hydrate resource off SW Taiwan.
| Identifer | oai:union.ndltd.org:TW/100NCU05134002 |
| Date | January 2012 |
| Creators | Che-Chuan Lin, 林哲銓 |
| Contributors | Andrew Tien-Shun Lin, 林殿順 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 202 |
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