H. Holl

Results of Stimulation Treatments at the Geothermal Research Wells in Groß Schönebeck, Germany

The aim of this work is to present results of previously performed fracture treatments in the geothermal research well GtGrSk4/05 at GroB Schonebeck. The fracture treatments included three hydraulic stimulations, two in the sandstone section of the Lower Permian and one in the volcanic section. In low permeable volcanic rocks we performed a cyclic waterfrac treatment over 6 days in conjunction with adding low sand concentrations. Flow rates of up to 150 1/s were realized with a total amount of injected water of 13170 m\ Monitoring water level in the offsetting well EGrSk3/90, which is 475 m apart at the final depth, showed a very rapidly water level increase due to the stimulation treatment. A possible explanation might be a fault zone in the volcanic rocks. It was known from previous treatments in the offsetting well that high permeable sandstones do not show a self propping effect, hence we performed two gel proppant treatments in these sandstones to maintain long-term access to the reservoir. A total amount of 100 to of high strength proppants with 500 m3 of cross-linked gel were injected during each treatment. The subsequent production test in conjunction with flowmeter logging showed the success of the treatments.

From Gas to Geothermal Exploration - A Case Study from the NE-German Basin

The sedimentary Lower Permian is a well known target for gas exploration in the North German Basin as part of the South Permian Basin System. In East Germany a huge quantity of well and 2D seismic data were generated from the 1960 s to 1990. We re-evaluated and re-processed some of these data to define potential geothermal reservoirs for power production. Since 2000, a non-productive gas exploration well, drilled in 1990 in the NE German Basin, is used as a geothermal in-situ laboratory for testing recovery strategies in terms if enhancing geothermal systems. After increasing the productivity of the well by several stimulation treatments, a second well was drilled from 2006-2007 to install a well doublet. The design of the new well differs considerably from gas well designs since geothermal wells need to satisfy some requirements like large diameters for housing the submersible pump, directional drilling to allow a set of parallel hydraulic fractures and drilling under near-balanced mud pressure conditions to minimize formation damage. Recently, a massive stimulation campaign increased the productivity of the new well considerably. This article shows the field development of a deep sedimentary reservoir as a integrated study from gas to geothermal exploration using latest technologies.

Field Trials of Plugging Oil and Gas Wells with Hydrated Bentonite

Many field trials have been conducted to explore the effectiveness of using hydrated bentonite as a sealing material for plugging and abandoning (P&A) operations of oil and gas wells. Many of those trials are reviewed here, including trials in Texas, New Mexico, Oklahoma, Wyoming and Queensland, most of which have not been previously reported. All of these trials have been successful, even though a few wells have been eliminated from the programs because they were found to be unsuitable. In most jurisdictions regulation changes are necessary to allow bentonite to be used in order to plug wells. This has been done in California, Texas and Oklahoma. In Wyoming it is currently permitted as the bottom plug in coal-bed methane wells. In Queensland a field trial has been allowed under the experimental materials clause in the regulations.

Constraining Static and Dynamic Properties of Naturally Fractured Reservoirs Using Microseismic

Natural fractures often provide preferential pathways for fluid circulation or provide enhanced connectivity between wells and the matrix for exchange of fluids and/or heat, and thus their properties control to a large degree both the production profile from producing wells and well injectivity. The discrete fracture network (DFN) approach provides a natural framework for describing and modeling of geological structures observed in the wellbore and from seismic, and their dynamic responses to changes in down-hole and reservoir pressures during injection/depletion. However, the approach is necessarily stochastic and requires assumptions about fracture extent and occurrence away from the well. In this paper we illustrate how microseismic monitoring during hydraulic stimulation provides a means to constrain both static properties (size, intensity, connectivity) and dynamic properties (hydraulic and mass balance apertures, geomechanical and compliance models) when used in combination with standard fracture interpretation and production logging. Using an example of a geothermal basement reservoir subjected to multi-stage stimulation, the workflow for fracture interpretation followed by coupled simulation of fracture flow and geomechanics is illustrated.