Well Test Analysis After Massive Waterfrac Treatments in a Sedimentary Geothermal Reservoir

Abstract

A series of stimulation experiments were carried out in a geothermal research well in the northeastern part of Germany with the aim of geothermal technology development. In a first attempt open hole hydraulic proppant fracturing treatments were conducted in two pre-selected sedimentary reservoir zones. They proved to be on the one hand technically demanding and on the other hand due to a suboptimal design less successful than expected. Nevertheless, the main inflow zones could be clearly identified. In a second step the concept of zonal selection and proppant application was abandoned and massive waterfrac treatments including small injection tests in the beginning were applied over the entire open hole interval of the well (3874-4294m). Due to bore instabilities the treatments had to be temporarily suspended. The problems were mastered by installing a pre-perforated liner. The wellbore was stabilized, the hydraulic accessibility to the pay zones as well as safer treatment conditions guaranteed for the continuation of the waterfrac experiments.
On this basis, changes of hydraulic parameters due to the various stimulations will be analysed and discussed. Evidence of the creation and properties of vertical fractures are retrieved from pressure response analyses. Data from production and flow back tests as well as from borehole images (BHTV and FMI) are being used for the analyses.
Therefore, the stimulation effect in terms of a productivity increase can be determined for the described concepts and improvements can be recommended for similar field experiments.