Session 6E: Well Construction & Completion

The current demand for energy, in addition to the efforts to reduce greenhouse emissions in the United States, has increased the importance of sustainable energy than ever before. In this respect, geothermal energy has become one of the most attractive solutions due to the huge amount of untapped resources that are present in many parts of the world. It is the only source of renewable energy that is not dependent upon climate conditions and remains in operation mode 98% of the time. However, extracting geothermal energy is challenging, as most conventional downhole tools fail under high-temperature, high-pressure (HPHT) conditions. Moreover, if these tools fail during the completion or production phase, it can compromise the well integrity and jeopardize project success. Therefore, this paper summarizes downhole tools, such as zonal isolation tool and flow valves developed under FORGE 1 project used for geothermal purposes, that can work under HPHT conditions. In addition, schematics of completions and working procedures will be presented to show how these tools would be installed and operated in the geothermal wells. These downhole tools have been tested at HPHT conditions and will be installed in one of the FORGE wells.

The potential for geothermal power is significant however the reality of delivering that potential in an economic way remains extremely challenging. This is especially true with regards to well completion technologies and methodologies due to the limitations in the performance of existing equipment in well conditions up to 300°C. A critical requirement for the successful stimulation of geothermal wells is effective well isolation technology.

This paper presents the research and development of a high temperature, retrievable, elastomer based isolation system that will enable controlled stimulation of an EGS reservoir. It details the test equipment design, test results and the engineering process for the development, testing and qualification of the elastomers chosen for the production packer. Focussing on reduced complexity with minimal moving parts this isolation system draws on experience gained in the oil and gas industry adapted to operate effectively at temperatures up to 300°C.

The paper will also discuss the development of the polymers and packer design to provide sufficient diametrical expansion to provide a seal and further to deliver the differential pressure performance of 6000psi required for these wells. It will also outline the qualification programme to API19OH and the results to date of a successful packer test at 225°C.

In this study calcium-free (and nearly Ca-free), aluminum-based cement was hydrothermally synthesized from sodium metasilicate (SMS) alkali-activated gibbsite, characterized, and evaluated for applications in supercritical and high-temperature (HT) CO2-rich geothermal wells. Hydrous ZrO2, silica flour, calcium aluminate cement (CAC), and microcarbon fibers (MCF) were used for matrix reinforcement. The hydrothermal synthesis was performed by autoclaving SMS-activated gibbsite at 300oC for 24 hours followed by exposures for 30 days in supercritical water (scH2O) at 400oC or 9 months in deep geothermal Newberry well at 325-350oC. Changes in thermal stability, porosity, mechanical properties caused by changes in phase compositions and phase transitions were evaluated. The absence of calcium in its composition allowed this cement to avoid carbonation under the HT geothermal well conditions and to preserve its mechanical properties, including high ductility. Differences in phase compositions observed under laboratory supercritical and well conditions are discussed.

Geothermal drilling presents unique challenges, including harsh environments, fractured formations, and dynamic operations. These challenges are imperative to address as global interest in green energy escalates. Consequently, the development of geothermal assets remains aggressive, necessitating innovative solutions to overcome drilling complexities.

The demanding drilling conditions require substantial effort, energy, and strategic thinking. Slow penetration rates, short bit life, and equipment damage are common issues, compounded by degradation of drilling fluid properties and mud system management difficulties. Understanding and mitigating these technical challenges are essential to minimize risks and enhance economic viability.

Experience and knowledge from the oil and gas industry are invaluable in navigating drilling challenges. While some strategies may prove effective, others lead to inflated costs. Tailoring drilling methodologies and systems for the unique geothermal environment is paramount to optimizing drilling projects and controlling expenses.

Addressing uncertainty, mitigating risks, and enhancing efficiency are primary objectives in geothermal drilling. A structured approach across planning, execution, and post-drilling phases is crucial. By integrating workflows and methodologies, leveraging drilling expertise, and fostering continuous improvement, operational costs can be reduced significantly.

This paper underscores the value of integrated management and drilling advisory in improving performance and reducing costs. Over three years Geothermal Project in West Java, Indonesia, 70-75% reduction in well cost per meter resulted in multimillion-dollar savings through knowledge management and accelerated learning.

The unique differences between geothermal and oil and gas wells require a tailored approach to well design, aimed at extending the lifespan of geothermal wells and addressing the critical challenges of operating mature geothermal fields. Oftentimes, geothermal wells have to intersect faults and other complex lithologies to maximize production. As a result, partial to massive losses lead to uncertainties in cementing operations and cement quality.

In some cases, channeling, development of micro-annulus, and cement degradation result in compromised well integrity and declining production. To address these integrity issues that shorten the effective life-of-well, a workover must be executed in a cost-effective way while ensuring that wells remain safe, efficient, and profitable to operate.

Welltec and a geothermal operator in the Philippines have worked together to address these challenges in four geothermal production wells in need of workover due to collapsed and parted casing within the 13-3/8” casing. A conventional workover by which wells are relined using a bridge plug was deemed unsuitable as drilling out the plug and chasing the debris to bottom could cause further damage to the liners subjected to low pH fluids. Furthermore, the risk of trapped fluid could lead to another casing failure. Thus, the solution requires a certain degree of cementing and control to achieve casing integrity.

This paper presents a solution design featuring high-temperature Metal Expandable Packer (MEP) technology and second stage cementing collar/s, and its application in case studies involving a geothermal production field in Leyte, Philippines. The study focuses on how MEP technology enables the reinstatement of well integrity without the need for a drill-out run.
By applying the learnings from previous deployments, the improved MEP facilitates long-string tieback and relining to ~1,300 meters, which was previously deemed unfeasible due to collapse issues, limiting deployment to depths of ~700 meters.

Designs for upcoming new corrosion-resistant-alloy (CRA) wells have been reviewed and evaluated to overcome very acidic environments.

These wells require immediate relining of production casings as part of the improvements from previously drilled CRA wells in the same sector and would utilize the MEP to avoid damaging the CRA casings during drill out of plugs.

This new design and strategy to include MEP technology in workover and drilling situations can be adapted to mitigate integrity issues resulting in premature failure, and extend the effective life of geothermal wells. This innovative drilling technology designed specifically for geothermal wells provides a pathway to greater repeatability, safety, and control to effectively harness geothermal resources.

A major technical hurdle for economically successful Enhanced Geothermal Systems (EGS) is flow conformance for equal heat harvesting from each fracture. Without flow conformance providing equal flow from injector to producer, the EGS could “short circuit” creating rapid cooling of produced fluid and subsequent electrical generation decline. This project’s goal is to build the tools necessary to construct and provide EGS flow conformance for uniformly distributed flow through fractures to maximize lifetime heat extraction.

This R&D project, called GeoThermOPTIMAL, is funded by the DOE Geothermal Technology Office through Utah FORGE and consists of the Colorado School of Mines with partners Tejas Research & Engineering and KSWC Engineering & Machining with Defiant Exploration. The team is developing and testing innovative devices for multi-stage stimulation incorporating a cemented casing frac sleeve with ports. In addition to the development of these frac sleeves, a downhole tractor is being developed for horizontal geothermal wells. This paper is a summary of the project thus far.

The cemented casing sleeves will be used to open a port for a hydraulic fracturing stage and then controlled using the tractor to selectively close a sleeve. Any specific sleeve can be actuated for stimulation with the same size frac ball, regardless of the number of sleeves for fracture stimulation. Then, afterwards, the injection profile can be optimized at individual sleeves to force injection fluid to move where needed to minimize thermal decline of the produced fluid. To close the sleeves, the wireline wellbore tractor with flow sensors would be deployed to first detect the fluid short circuit and engage with the sleeve, close it, and remove the short circuit.

In addition to tool building, mathematical analyses of recent laboratory and field data indicates that the current two-well, injection-production configuration (Utah FORGE and Fervo Energy’s Nevada Pilot test), connected with multiple hydraulic fractures, is the most promising, practical method for extracting heat from hot-dry-rock (HDR) geothermal systems. For additional heat recovery, modeling shows the current two-well system could be expanded to a three-well system consisting of one injection well and two symmetric producing wells connected with the same hydraulic fractures that emanate from the injection well. In addition, to enhance the understanding of how the sleeves will behave in-situ, various levels of modeling have also been incorporated in the project to assess how the sleeves enhance the EGS process. Near-wellbore breakdown processes have been modeled to determine failure behaviors as the hydraulic fractures initiate from the well.