Adapting Unconventional Oil And Gas Completion Technology: A Key Factor In Reducing Risks Associated To Egs Projects

Abstract

Technical and economic success of deep geothermal development relies on our ability to reduce drilling risks and to reliably complete these wells, but drilling and properly completing deep geothermal wells remains a risky business. In the closely related oil and gas activities, the risk taken by the investors is balanced by the high reward that successful projects achieve by immensely offsetting the losses of the failed wellbores. Until today, the geothermal energy experiences similar risks, however, the potential reward is limited by the competition with other energy sources, in a heavily regulated market. The economical acceptability of geothermal power generation requires low risk drilling and completion technologies that would work under many different geological conditions. When two wells are drilled into a petro-thermal formation, sometimes referred to as hot dry rock (HDR), there is normally no clear circulation path between these wells and when this path exists, the transmissivity is so low that no economical project is possible. Enhanced geothermal systems (EGS), in these circumstances is closer to reservoir creation than to conventional reservoir stimulation. Therefore there is a lot at stake, for geothermal developers, in understanding EGS creation, and in developing technologies that achieve the EGS designed size and transmissivity. The EGS becomes an economical proposition only when enough rock surface can be contacted by the geothermal fluid, and when the flow path runs smoothly through a sufficient rock volume. Then, energy depletion is minimized and the project can run over a long period, compatible with a positive net present value (NPV). To that end, the well design and its completion system have to be engineered to maximize the chances of properly creating and operating the EGS. In this paper, lessons learnt from past geothermal projects are reviewed and analyzed to propose a multi-stage system as a mean of reducing some of the risks associated to geothermal wells. Current oil and gas (namely “unconventional”) completion technologies related to multi-stage stimulation have been reviewed and different options are discussed in the scope of a deep geothermal hot dry rock project. The necessary tests before running different parts is also discussed. Other options for reservoir creation are debated with their potential benefits and associated risks; the developments that could make them work in an EGS project are discussed.

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