Rock permeability and fluid pressure at the KTB: Implications from laboratory - And drill hole - Measurements

Abstract

Rock permeability and the fluid pressure were investigated at different scales at the two drill holes of the Continental Deep Drilling Program (KTB). Drill hole tests and fluid inclusion investigations both implicate the existence of hydrostatic fluid pressure in situ with respect to salinity of the formation fluid. Matrix permeability and in situ values from hydraulic tests differ up to three decades with higher values in situ. Further on, the pressure dependence of core permeability and in situ determined values differ significantly. All these observed effects support the well known theory of scale variance. This conclusion is supported by observations of hydraulic communications between both drill holes. These scale effects implicate a pronounced hydraulic heterogeneity of the KTB surroundings. Therefore, stochastic network modelling with parameters derived from structural borehole measurements and under the consideration of the observed permeabilities were performed. Under the presumption of existing driving forces fluid transport takes place dominantly on discrete connected pathways characterised by fracture width, fracture length and fracture orientation and is subordinate in the rock matrix. Copyright ©1999, Éditions Technip.