Conversion of oil and gas wells to geothermal reinjection
Author: Vedran Zikovik
Year: 2019
Supervisors: Sverrir Þórhallsson, Juliet Newson
Abstract:
Number of old, disused and abandoned oil wells around the globe is counted in millions. If just a small fraction could be converted for geothermal utilization, it could significantly reduce costs and environmental impact compared to making new wells from scratch. The focus of this project is conversion of existing oil and gas wells to geothermal reinjection for potential geothermal utilization in north-west part of Croatia. Legrad field is an almost depleted oil and gas area with 19 wells that are potential candidates. Their reuse could potentially result in mitigation of costs and environmental impact by not having to drill new wells, while achieving similar reinjection objectives. Drilling new wells can be rather expensive and risky even in a familiar and relatively well-known locations since there are many unpredictable issues that can occur during drilling, such as temperature and pressure, formation change, permeability and porosity etc. This thesis MSc report consists of few main chapters: well selection, well design, cost analysis and environmental impact. The well selection chapter will summarize most important data of all Legrad wells in a form of a database, criteria for well selection will be developed based on most important reinjection parameters, and finally a grading method will be proposed on which each candidate well will be assessed. The well design chapter will cover the design and status of existing wells and the suggested re-design. The workover and drilling requirements will be proposed for each candidate, along with a new wellhead construction with respect to the reinjection requirements. Cost analysis will tackle the economic feasibility of the project and financial study will cover the estimated costs of workover and drilling works, equipment and material, wellhead and pipeline connection. Comparisons with the cost of drilling new wells are made to determine the profitability of each scenario. Environmental impact chapter will address most important effects on the nature due to the drilling and workover projects and the impact of each well candidate will be evaluated.