Reappraisal Of Dinantian And Rotliegendes Geothermal Reservoirs By Seismic Pre-Stack Reprocessing

Abstract

The deadlines for the 2020 climate goals of the Dutch national government are approaching fast. These goals include combatting CO2 emissions and to make the Dutch energy mix more sustainable. Means to achieve these goals are among others to intensify CO2 capture and underground storage (CCUS) and production of geothermal energy. An exam- ple of increased use of geothermal energy is the national Ultra Deep Geothermal (UDG) project, which aims at evaluating ultradeep geothermal pilot projects in Dinantian Carbonates at 4-7 km depth. Due to these large depths, drilling costs are high and constitute the main expenditure for these geothermal projects. As budgets and return on investment for geothermal projects are currently considerably lower than oil and gas projects, de-risking geothermal projects is of para- mount importance. High risk and thus high potential costs are often a show-stopper here. Seismic imaging is currently the method with highest resolution and the largest de-risking capability for geothermal projects. It is a typical cross-over technology that profits from historical and recent advancements in oil, gas and mineral exploration. Advances in seismic imaging are three-fold: advances in seismic acquisition, seismic processing and seismic interpretation/analysis. To benefit from these, either new seismic data can be acquired or existing data can be reprocessed. Both types of data should be re-interpreted. A prime question arises whether new acquisition or existing reprocessing is the more capable and cost-effective solution for geothermal projects. The obvious answer is that this is project- specific, nevertheless general statements and recommendations can be made about this issue. To answer this question, we developed a fast-track pre-stack reprocessing workflow for 2D seismic lines. The workflow is a combination of 1) industry-standard processing techniques such as pre-stack time migration, demultiple, deconvolution, statics and 2) novel techniques like broadband processing, adaptive non-linear de-noising and selective stacking. The workflow is demonstrated on several vintage 2D off- and onshore lines which were obtained as field tapes with observer logs from archives. The latter proved a challenge by itself. Results show that the pre-stack reprocessing considerably improves images of Dinantian and Rotliegendes reservoirs. Especially better spatial focus by new pre-stack migration and temporal focus by new broadband deconvolution have improved top- and bottom reservoir continuity and fault delineation. Onshore data benefited more from this improvement than offshore data. Since 1) the enhancements are substantial, 2) fast-track reprocessing can be done in less time than the original processing and 3) the whole effort of new data acquisition is absent, seismic reprocessing presents a cost- effective way to de-risk geothermal projects. As such it makes for an attractive alternative to new seismic acquisition.

AAPG Datapages/Search and Discovery Article #90345 © 2018 AAPG European Region, Geothermal Cross Over Technology Workshop, Part II, Utrecht, The Netherlands, April 17-18, 2018