RISK ASSESSMENT FOR OIL AND GAS TO GEOTHERMAL WELL CONVERSION AND COMPLETION DESIGN PROPOSALS

Abstract

With the global push toward net-zero carbon emissions, oil and gas production will begin to decline, leaving behind thousands of abandoned wells that need to be addressed. In Oklahoma there is an estimated 17,000 orphaned oil in wells, leaving a backlog of wells needed to be plugged and abandoned. Pawnee Nation is leading the charge to handle this vast inventory by converting old oil and gas wells into geothermal wells. Repurposing these wells offers significant cost savings, as they do not require drilling and typically demand minimal completions to be made suitable for geothermal use. However, before repurposing and converting a well, the risk associated with such an action and the completion design must be taken into account before breaking ground on such a project. This thesis will focus on the risk assessment for converting oil and gas wells into geothermal wells along with completion designs for said wells. The risk assessment will take the qualitative analysis of risk associated for each element of the wells and convert that analysis into a usable quantitative variation to more easily recognize the elements that cause the most risk. The completion designs will offer insight and options for each setup, along with the limits for each system. By identifying risks through the integration of the Feature, Event, and Processes (FEP) framework with the Interaction Matrix (IM), Incident Potential Matrix (IPM), and Cause-Effect plot diagram it will be easier to identify which element is the most critical to each system. When the most at risk elements are known, it is easier to focus on them, understand why they are riskier, and reduce the risk for each. A completion design allows for a more complete understanding of the forces acting within the system, and therefore it is possible to design around the more critical elements and make them more resilient to catastrophic failure. The objective of this thesis is to identify which portions of a well or wells are most at risk for catastrophic failure when converting an old oil and gas well into a geothermal well. It gives a complete well completion design to assist operators in choosing their wellbore equipment and understand flow rates to help with surface equipment selection. This thesis will first identify critical elements within the well system via the FEP, then placed in the IM to assess the effect of one element on another. The IPM assigns a risk value based on severity and probability, as determined by experts in the field. After the risk values are established in the IM, a cause-effect calculation generates a plot that indicates which elements are critical and have the potential to compromise well integrity and cause catastrophic events. This risk assessment exercise enables the implementation of remedial measures in advance, ensuring the well is suitable for retrofitting into geothermal applications. It is also crucial to understand what options are available when converting these oil and gas wells into geothermal wells. This thesis contains two proposals, a single well and a doublet system that goes in depth into tubing selection, expected flow rates, forces acting on the tubing and subsequently packer, and also a brief cost analysis and recommendation. The findings of this risk assessment show that single wellbores score higher than a dual well system when it comes to converting these wells. The fluid and temperature were the biggest effecters in each system, and the casing and wellhead were the elements most effected by other elements, and could be the source of catastrophic failure. As far as completion designs go, using the 3.5” tubing seems to allow for the most balanced flow rate in both single and double well system, while still leaving room for ESP cables.