Hydraulic characterisation of the Stuttgart formation at the pilot test site for CO2 storage, Ketzin, Germany

Abstract

The paper presents an approach for the interpretation of hydraulic tests of a CO 2 storage reservoir. The sandstone reservoir is characterised by a fluviatile channel structure embedded in a low-permeability matrix. Pumping tests were carried out in three wells, with simultaneous pressure monitoring in each well. The hydraulic parameters (permeability and storativity) and the boundary configurations were calibrated using three different approaches: (i) parameter calibration and type curve interpretation for single-hole tests, (ii) calibration of the entire build-up phase for cross-hole tests, and (iii) calibration of the initial pressure response for cross-hole pumping tests. In addition, the arrival time of the pressure response was determined and provides additional information about the pathways of hydraulic connection. The measured pumping test permeabilities of the formation were much lower than those measured on the cores, which is very unusual. The pumping test permeabilities are mainly between 50 and 100 millidarcy (mD), while core samples show a mean aquifer permeability of 500 to 1,100 mD. Based on this it was concluded that some kind of continuous low permeability structure exists, which was supported by core material. Three possible aquifer configurations were considered. The first and second were derived from traditional pumping test analysis and were conceptualised using flow boundaries. Each of the analyses provides a different result. A method was developed in which these differences were resolved by interpreting the pressure response with respect to its spatial and temporal sensitivity. This solution lead to a third configuration which was mainly based on spatially-variable permeabilities. Taking into account the pumping test results, the geological background and the behaviour of injected CO 2 , we consider only the third configuration to be realistic. The results are in good agreement with modelled CO 2 arrival times and pressure history.

Numerical simulations of CO2 arrival times and reservoir pressure coincide with observations from the Ketzin pilot site, Germany

“…As there is no indication of low horizontal fault permeability based on hydraulic tests undertaken (Wiese et al 2010) and unpublished operational data of the gas storage operation, all seven faults implemented in the reservoir model were assumed to be horizontally conductive for fluid flow. According to permanent pressure and isotope monitoring in an indicator horizon located in the Exter Formation (about 180 m above the Stuttgart Formation), regional communication between that indicator horizon and aquifers in the Jurassic or the Stuttgart Formation may exist (Wiese et al 2013).…”

“…The Ketzin pilot site located in the State of Brandenburg, Germany, was the first European on-shore site for CO 2 storage in a saline aquifer and is now operated for[4 years Würdemann et al 2010 Möller et al (2012) covering all relevant data for simulations from the start of injection up to the end of the year 2011.…”

Influence of drill mud on the microbial communities of sandstone rocks and well fluids at the Ketzin pilot site for CO2 storage

“…For the completion phase, a swelling rubber packer technology requiring the use of fresh water was used to facilitate stage cementing. Hydraulic tests performed 12 weeks after well completion revealed that the injectivity was much lower than expected (approximately 0.07 mD) (Wiese et al 2010). The low well injectivity was attributed to amorphous iron sulfide, which blocked the pore throats ).…”

Comparison of the microbial community composition of pristine rock cores and technical influenced well fluids from the Ketzin pilot site for CO2 storage

“…The operation was performed using a water-based CaCO3/bentonite/organic polymer drill mud containing carboxymethylcellulose (CMC), with the addition of biocide, comprising organic amines, to prevent microbial degradation and reduce the souring of the mud. Prior to CO2 injection, pumping tests were performed on all wells (Wiese et al 2010). To remove residual drill mud from the wells a so-called gas lift was performed.…”

“…The fluids were sampled directly from the wellhead, collected in sterilized glass bottles, cooled and transferred to the laboratory for further analyses. During the pump test of the DOW, 93 m³ of fluid was produced (details are given in Wiese et al 2010). Fluids were sampled after 4,27,30,40,55,61,79, 93 m³ of production.…”