The Stimulation of a Sedimentary Geothermal Reservoir in the North German Basin: Case Study Gro? Schˆnebeck

Abstract

In order to make the generation of geothermal
electricity in a sedimentary reservoir rocks possible a
deep former gas exploration well was reopened and
deepened in 2000 to 4294 m depth. An in-situ
downhole laboratory was established in this well with
the purpose of developing appropriate stimulation
methods to increase permeability of deep aquifers by
enhancing or creating secondary porosity and flow
paths.
The goal is to learn how to enhance the inflow
performance of a well from a variety of rock types in
low permeability geothermal reservoirs. Proppant-gel-
frac techniques as well as waterfrac techniques
were used in several different experiments. During
the proppant-gel-frac two intervals of Rotliegend
sandstones were hydraulically stimulated in January
2002. The experiment design comprised isolating the
bottom boundary of the interval of interest by filling
the bottom of the well with sand. The top of the
interval was sealed with a mechanical packer. High-viscosity
fluid with proppant was employed for
stimulation. Flow rates were increased significantly,
and a fracture with a length of 150 m was generated
due to this operation. However, the productivity
observed was insufficient for power production.
Further stimulation of the reservoir rocks in this well
was performed in two experiments in winter and fall
2003 using the waterfrac technique. More than 15000
m? water was injected in different pressure steps with
flow rates up to 80 ls -1 . Mechanical reacting reservoir
properties were observed at injection flow rates
above 9 ls -1 . Recent data of a production test show a
productivity of 14 m?h -1 MPa -1 .