Geological Processes Related to Seafloor Thermal Structures offshore SW Taiwan
Date Issued
2014
Date
2014
Author(s)
Chen, Liwen
Abstract
Geological processes on thermal patterns are important for understanding the energy potential for hydrocarbon exploration; however, thermal patterns below the seafloor are always difficult to derive. So we combined the geophysical in-situ thermal measurements and the wide spreading bottom-simulating-reflectors (BSR; bottom of the gas hydrate stability zone identified from the seismic data) collected recent years, to model the temperature fields beneath the seafloor. Using the advantage of the physical property of gas hydrates, we proposed two methods for analyzing the regional thermal patterns offshore SW Taiwan, and successfully derived several geological processes related to seafloor thermal structures according to our study results.
First, we used BSR-based geothermal gradient patterns to derive vertical fluid flow models from Peclet Number analyses. We found the regional 1-D fluid flow rates are ranging from 6 cm/yr to 43 cm/yr, including several prospect sites for gas hydrate exploration. From passive margin to active margin, the increasing of fluid flow rate might be related to more active dewatering near the toe of the trench; in the active margin, there are higher fluid flow rates when the frontal thrust climbs onto the continental slope of the passive margin in the collision zone. Then, considering about the topography effect, we used temperature discrepancies between BSR-based and modeled temperatures, which are derived from the finite element code – Pecube, to reflect the regional cooling and heating effects. Therefore we could further analyze and compare the regional geological processes based on our study results.
Finally, we proposed several geological processes that can affect regional thermal patterns: (1) From studying the 3-D cube in lower Fangliao Canyon of the upper slope domain, we discovered the regional heating effect from the diapir was reduced 38 % by recent sedimentation; (2) relatively, we found intermittent upward fluid migrations along the fault planes brought the heating effects in Yung-An Ridge of the lower slope domain; (3) as well as in Frontal Ridge, we found possible extensive fluid migration from the faulting pathways to cause heating effects at the toe of the accretionary wedge. (4) Related to the MTD (mass-transport deposits) effect occurred in upper reach of the Penghu Canyon, it caused the heating and cooling effects at the uphill and downhill respectively. (5) Beside, in the canyon incision region of Formosa Ridge, we found the cold seawater had been laterally siphoned into the ridge in the traverse direction, and diffused along the ridge strike to disturb the temperature fields. In this study, our contribution is developing the simulation methods for better using our current data to analyze thermal structures; in the future, we could improve our simulation results to get more quantifiable flux information for the energy research offshore SW Taiwan.
Subjects
地質作用
熱效應
地溫梯度
佩克萊數（Peclet numbers）
Pecube
海 底仿擬反射
台灣西南海域
Type
thesis
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