超額孔隙水壓對於地殼強度扮演了重要的角色，而對超額孔隙水壓最有影響的參數為滲透率、孔隙率以及比儲水係數，其中比儲水係數主要與孔隙的壓縮性有關。本研究以滲透率/孔隙率量測儀(YOKO2)，量測砂岩、粉砂岩/頁岩於有效圍壓從3MPa增加到120MPa下岩心的滲透率與孔隙率(岩心取自台灣車籠埔鑽井計畫的Ａ、Ｂ井的岩心)。總體而言，砂岩之滲透率範圍為10-13~10-14m2 ，粉砂岩與頁岩之滲透率範圍為10-16~10-19m2 ，粉砂岩/頁岩對於應力的敏感性較砂岩高(即滲透率變化隨應力變化較大)。砂岩、粉砂岩及頁岩其孔隙率範圍分別為15%~19%、8%~11% 以及 13%~14%，根據試驗結果發現不同的岩性，孔隙率對應力的敏感性似乎沒有太大的差異。根據試驗結果發現，滲透率與孔隙率隨應力變化的行為，可利用冪次函數模式或指數函數模式加以描述。利用冪次函數模式或指數函數模式，可以獲得孔隙敏感指數 。由冪次函數所求得的孔隙敏感指數 ，砂岩的範圍為 3.26~5.47 (加壓) 以及2.34~3.08 (解壓); 粉砂岩/頁岩的範圍為 25.98~47.50 (加壓) 以及 6.91~46.43 (解壓) ， 值越高，表示越容易產生超額孔隙水壓。根據孔隙率冪次函數模式所推求得的比儲水係數對於應力比較敏感，砂岩的範圍為 ~ ，粉砂岩/頁岩的範圍為 ~ 。藉由Gibson方程式中以及利用有限差分法求解，我們可以計算超額孔隙水壓的產生與消散，根據計算結果發現地下流體流動參數由冪次函數模式所求得因沉積物載重造成的超額孔隙水壓，將比利用指數函數模式計算所得之超額孔隙水壓要小，因此，如果要分析地殼中因沉積物載重產生之超額孔隙水壓，應慎選地下流體流動特性之應力依存性模式。 Overpressure plays an important role on thrust faulting of fold-and-thrust belt. In petroleum geology, understanding abnormally high pore pressure is also important for studying primary petroleum migration and drilling, as well as for analyzing sedimentary basins. The parameters which have most influential to overpressure are permeability, porosity and specific storage coefficient. Accurate measuring of the stress dependent fluid flow properties is essentially important to explore the fluid percolation process in crust. An integrated permeability/porosity measurement system-YOYK2 was utilized to measure the pressure-dependency of permeability and porosity of core samples from Taiwan Chelungpu fault Drilling Project, Hole-A and Hole-B. The measured permeabilities of sandstone and siltstone/shale are 10-13~10-14m2 and 10-16~10-19m2 under confining pressure of 3~120 MPa. The permeability of siltstone and shale is more sensitive to confining pressure than that of sandstone. The measured porosities of sandstone, siltstone and shale under confining pressure of 3~120 MPa are 15%~20%, 8%~11% and 13%~14%, respectively. Meanwhile, different rock types have almost identical pressure-sensitivity of porosity. Two pressure-dependent models, power law and exponential relation, for describing the pressure-dependent permeability/porosity were used to fit the experiment results. The calibrated porosity sensitivity exponent is estimated to range form 3.26 to 5.47 (loading) and range form 2.34 to 3.08 (unloading) for tested sandstones by using a power law to describe the pressure-dependency of permeability/porosity. The porosity sensitivity exponent is estimated to range from 25.98 to 47.50 (loading) and from 6.91 to 46.43 (unloading) for tested siltstone and shale which is much higher than that of sandstone. The specific storage coefficient (related to the pressure-dependent porosity) also demonstrates more pressure sensitivity for adopting a power law than using an exponential relation. The calculated specific storage is ranged from to for sandstone and from to for siltstone and shale when the confining pressure increasing from 3 MPa to 120 MPa. The pressure-dependent specific storage coefficient, as well as the permeability/porosity, can be incorporated into a non-linear Gibson equation to calculate the overpressure generation and dissipation by finite difference method. The calculated overpressure using power law to describe the pressure-dependent fluid flow properties is less than the one using exponential relation. Proper selection of the pressure-dependent models of fluid flow properties is critical for calculating the overpressure in crust.
