Hydraulic observations from a 1 year fluid production test in the 4000 m deep KTB pilot borehole

Abstract

A long-term pump test was conducted in the KTB pilot borehole (KTB-VB), located in the Oberpfalz area, Germany. It produced 22 300 m 3 of formation fluid. Initially, fluid production rate was 29 l min )1 for 4 months, but was then raised to an average of 57 l min )1 for eight more months. The aim of this study was to examine the fluid parameters and hydraulic properties of fractured, crystalline crusts as part of the new KTB programme 'Energy and Fluid Transport in Continental Fault Systems'. KTB-VB has an open-hole section from 3850 to 4000 m depth that is in hydraulic contact with a prominent continental fault system in the area, called SE2. Salinity and temperature of the fluid inside the borehole, and consequently hydrostatic pressure, changed significantly throughout the test. Influence of these quantities on variations in fluid density had to be taken into account for interpretation of the pump test. Modelling of the pressure response related to the pumping was achieved assuming the validity of linear Darcy flow and permeability to be independent of the flow rate. Following the principle 'minimum in model dimension', we first examined whether the pressure response can be explained by an equivalent model where rock properties around the borehole are axially symmetric. Calculations show that the observed pressure data in KTB-VB can in fact be reproduced through such a configuration. For the period of high pumping rate (57 l min )1 ) and the following recovery phase, the resulting parameters are 2.4 · 10 )13 m 3 in hydraulic transmissivity and 3.7 · 10 )9 m Pa )1 in storativity for radial distances up to 187 m, and 4.7 · 10 )14 m 3 and 6.0 · 10 )9 m Pa )1 , respectively, for radial distances between 187 and 1200 m. The former pair of values mainly reflect the hydraulic properties of the fault zone SE2. For a more realistic hydraulic study on a greater scale, program FEFLOW was used. Parameter values were obtained by matching the calculated induced pressure signal to fluid-level variations observed in the KTB main hole (KTB-HB) located at 200 m radial distance from KTB-VB. KTB-HB is uncased from 9031 to 9100 m and shows indications of leakage in the casing at depths 5200-5600 m. Analysis of the pressure record and hydraulic modelling suggest the existence of a weak hydraulic communication between the two boreholes, probably at depths around the leakage. Hydraulic modelling of a major slug-test in KTB-HB that was run during the pumping in KTB-VB reveals the effective transmissivity of the connected formation to be 1 1 2 to 2 orders of magnitude lower than the one determined for the SE2 fault zone.

Fluid induced seismicity guided by a continental fault: Injection experiment of 2004/2005 at the German Deep Drilling Site (KTB)

“…During the fluid production phase of the experiment induced seismicity was absent. Hydraulic permeability was estimated to be around 2 × 10 −15 m 2 [ Stober and Bucher , 2005; Gräsle et al , 2006].…”

Simulation of effects of agricultural activities on groundwater level by combining FEFLOW and GIS

“…•839' for groundwater simulation and has been used to study ground water levels changes (Sarwar & Helmut 2006;grasle et al 2006), solute movement in ground water (Barber et al 1996;Diersch & Kolditz 1998;gernoth & Jurgen 2000;Michael et al 2005;Reynolds & Marimuthu 2006), and heat flux (Yang & Monica 2006). In this study, the Minqin oasis, a typical arid-inland region is selected as the study area and the groundwater model will be developed using FEFLoW and gIS.…”

Two Massive Hydraulic Tests Completed in Deep KTB Pilot Hole

“…The bulk hydraulic permeability of the SE2 fault system was found to be 2 x 10 -15 m 2 (hydraulic conductivity = 10 -8 m s -1 ), about one order of magnitude higher than rocks outside SE2 (Stober & Bucher, 2005;Gräsle et al, 2006;McDermott et al, 2006). The fault system clearly dominates fluid flow on the regional scale.…”

“…Specific results of the injection test and of some of the companion experiments can be summarized as follows. About 3000 micro-seismic events were detected by the The fluid level in KTB-HB rose sharply several days after the injection started in KTB-VB (Gräsle et al, 2006). KTB-HB became artesian in October 2005 (Fig.…”