Estimate the in-situ stress in HsinChu and MiaoLi from subsurface geological data
Speaker: Jen-Ru Liau
Abstract
This study uses the subsurface geological data from well drilling in the past 40 years to estimate the in-situ stress in Hsinchu and Miaoli. The magnitude of the vertical stress (S v ) was calculated from the formation density log data in Tiehchenshan (TCS) and Chuhuangkeng (CHK) region, and the gradient is about 22.56 MPa/km. From the formation repeat tests collected in Chingtsaohu (CTH), Paoshan (PS), Chinshui (CS), Chuhuangkeng and Tiehchenshan regions can get the magnitude of pore pressure here. Hydraulic fracturing data including leak-off tests (LOTs) and fluid injection undertaken in cased and cemented wellbores through perforation (called mini-fracs) from this area provide the estimate of the minimum horizontal stress (S hmin ). And the gradient of the S hmin is about 18.41 MPa/km. The magnitude of maximum horizontal stress (S Hmax ) was constrained by frictional limits from Anderson's theory of faulting and by presence of drilling induced tensile fractures. Assume that the frictional coefficient is 0.6; the gradient of the S Hmax is about 32.56 MPa/km. The stress magnitudes determined indicate a predominantly strike-slip stress regime in Hsinchu and Miaoli; nevertheless, some wells are transitional between strike-slip (in sandstone) and reverse fault stress regimes (S Hmax > S hmin = S v ).
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