Fishbone drilling (FbD) is a specialized drilling method designed to improve energy extraction from subsurface reservoirs by increasing contact with the rock formations. By utilizing a multilateral branching well design, FbD allows for enhanced recovery in both geothermal and hydrocarbon reservoirs.
This article provides a detailed exploration of the methodologies, field applications, design optimization, and environmental advantages of FbD. It also highlights key challenges and discusses potential future research directions for expanding the technology's use in both conventional and renewable energy systems.
Why Is Fishbone Drilling a Promising Technology for Energy Extraction?
The demand for efficient and sustainable energy extraction has intensified the need for innovative drilling techniques that can handle complex geological formations. FbD is one such technology that has shown significant promise in the hydrocarbon and geothermal industries. Characterized by multiple laterals or branches that extend from the main wellbore, seen in Fig. 1, FbD increases the surface area of the well in contact with the reservoir, resulting in enhanced production rates and improved reservoir drainage (Ndulue et al., 2023).
Conventional drilling methods, such as vertical or horizontal drilling, often face difficulties in highly fractured or low-permeability formations. These challenges can lead to production problems, higher operational costs, and environmental concerns. FbD has been identified as a solution to these issues, particularly in enhancing production from unconventional reservoirs and minimizing environmental impacts (Abdulazeem and Alnuaim, 2016).
How Can Fishbone Well Design Be Optimized?
The primary objective of FbD design is to maximize reservoir contact while balancing operational complexity and cost. Some of the critical parameters include (Fig. 2):
- Number of branches: The number of branches affects how much of the reservoir can be accessed. Studies show that increasing the number of branches results in higher production rates, but after a certain threshold, the additional cost and complexity may not yield proportional benefits. For example, Manshad et al. (2019) demonstrated that wells with four branches increased production, but adding more branches did not lead to significant improvements.
- Branch length and angle: The optimal length and angle of each branch depend on the reservoir’s geometry and rock properties. Longer branches increase the well's drainage area but can also complicate the drilling process. Research by Xing et al. (2012) found that branch lengths of 200 to 300 m were ideal for maximizing production in low-permeability reservoirs. Branch angles between 30° and 45° have been shown to provide optimal reservoir contact without excessive interference between branches.
- Branch Spacing: Spacing between adjacent branches must be carefully calculated to avoid overlapping drainage areas, which can lead to reduced efficiency. Simulation studies suggest spacing of 80 to 150 m between branches for optimal production in typical hydrocarbon reservoirs (Xing et al., 2012).
FbD design optimization relies on advanced 3D reservoir simulations to model fluid flow through the main borehole and lateral branches, allowing detailed analysis of how parameters like branch number, orientation, and spacing impact production (Fig. 3).
These simulations provide crucial insights into flow dynamics, pressure distribution, and recovery efficiency, in contact with the reservoir formation, enabling precise adjustment of well configurations. Sensitivity analysis helps identify the optimal design by testing variations in key parameters, ensuring maximum reservoir contact and production efficiency.
This adaptive approach accounts for geological uncertainties, optimizing FbD designs to specific subsurface conditions for improved recovery and reduced operational costs (Ouadi et al., 2023b).
What Are the Applications of Fishbone Drilling?
FbD has been successfully applied in various energy extraction sectors, particularly in geothermal energy production and hydrocarbon recovery from unconventional reservoirs.
Geothermal Energy Production
FbD has proven to be an effective method for enhancing geothermal energy extraction, particularly in enhanced geothermal systems (EGS). By increasing the surface area of the well in contact with the heat-bearing rock, FbD enables more efficient heat transfer, resulting in higher energy production rates. In a study conducted in the Williston Basin, North Dakota, FbD was shown to increase geothermal energy output by 30% compared to conventional drilling techniques (Ouadi et al., 2023a) (Fig. 4).
The multiple branches also reduce the injection pressure needed in geothermal operations, allowing for more stable and sustainable long-term energy production (Mohamed et al., 2021).
Jos Okkerman, geothermal business development manager for Fishbones AS, highlighted the Norwegian company’s innovative fracturing-free technology for geothermal well enhancement. Using water-based fluids, Fishbones' approach improves reservoir connectivity and production efficiency while complying with global environmental standards, especially in regions where hydraulic fracturing is restricted. The company is targeting the European hydrothermal market and ESGs in the US with plans to expand into areas like carbon capture and storage and lithium extraction (Fishbones, 2023).
Hydrocarbon Recovery
FbD has been particularly beneficial in high-permeability reservoirs. For example, in the Middle East, a fishbone well design increased production by 393%, though drilling costs rose by 130% (Manshad et al. 2019). Similar success has been reported in other regions, including Russia, Norway, and the UAE, with productivity gains of up to 300% in tight reservoirs (Ndulue et al., 2023). This is due to the ability of FbD to penetrate multiple zones within the reservoir, intersecting some of the naturally fractured reservoirs, thereby maximizing the recovery factor.
What Are the Environmental Benefits of Fishbone Drilling?
FbD offers significant environmental advantages over traditional drilling methods. By increasing reservoir contact and enhancing production efficiency, FbD reduces the need for extensive hydraulic fracturing, thereby lowering the number of wells required to meet production targets. This results in substantial reductions in water and chemical usage, as well as minimizing surface land disturbance.
According to Fishbones AS, their technology can cut CO2 emissions by as much as 95% compared to conventional hydraulic fracturing, offering operators an efficient and environmentally friendly alternative (Fishbones 2022). Furthermore, the precise control over stimulation and reduced drilling time makes FbD an attractive option for those looking to minimize their environmental footprint while maintaining high production levels (Ouadi et al., 2023c). This combination of efficiency and reduced environmental impact positions FbD as a leading solution for sustainable energy extraction.
What Are the Challenges for Fishbone Drilling?
The design and implementation of FbD wells require specialized equipment and expertise. The complexity of the branching system makes well-trajectory control and geosteering critical, especially in fractured or highly heterogeneous reservoirs. Additionally, accurate prediction of production rates from FbD wells remains a challenge due to the interaction between the branches and the reservoir (Al-Rbeawi and Artun, 2019).
What Is the Future of Fishbone Drilling?
Future research should focus on developing more-accurate models for predicting FbD well performance. There is also a need for advanced real-time monitoring systems that can provide feedback on wellbore conditions and allow for adjustments during drilling. Another area of interest is the application of FbD in carbon capture, utilization, and storage projects, as well as hydrogen storage in underground formations. These emerging fields present opportunities for further expanding the application of FbD technology while contributing to global efforts to reduce greenhouse gas emissions (Ouadi et al., 2023b).
Moreover, the technology's application in existing infrastructure, such as repurposing abandoned oil and gas wells for geothermal applications, offers a viable solution to the challenges associated with drilling new wells. This approach can leverage existing infrastructure, thus reducing environmental impact and operational costs (Merzoug et al., 2023).
For Further Reading
SPE 182757 New Method to Estimate IPR for Fishbone Oil Multilateral Wells in Solution Gas Drive Reservoirs by A. Abdulazeem, S. Alnuaim; King Fahd University of Petroleum and Minerals.
Fishbone Type Horizontal Wellbore Completion: A Study for Pressure Behavior, Flow Regimes, and Productivity Index by S. Al-Rbeawi, E. Artun; Middle East Technical University.
The Fishbone Technology: To Use or Not to Use? by M. El Ghandour, Egypt Oil and Gas.
Fishbones Technology for the Geothermal Market: An Alternative Approach for Enhanced Well Performance by J. Okkerman, Fishbones.
Economic and Productivity Evaluation of Different Horizontal Drilling Scenarios: Middle East Oil Fields as Case Study by A. Manshad, J. Ali, Soran University; M. Dastgerdi, Islamic Azad University; et. al.
SPE 215062 Selection Criteria for Repurposing Oil And Gas Well to Geothermal Heat Extraction by A. Merzoug and R. Okoroafor, Texas A&M University.
Significance and Complications of Drilling Fluid Rheology in Geothermal Drilling: A Review by A. Mohamed, S. Salehi, and R. Ahmed, University of Oklahoma.
A Comprehensive Review of Fishbone Well Applications in Conventional and Renewable Energy Systems in the Path Towards Net Zero by U. Ndulue, H-PTP Energy Services Ltd.; O. Tomomewo, H. Khalifa, University of North Dakota.
A New Insights into Fishbone Well Deliverability Analysis, Case Study: Solution Gas-Drive Reservoir in Algeria by H. Ouadi, University of North Dakota.
Design and Performance Analysis of Dry Gas Fishbone Wells for Lower Carbon Footprint by H. Ouadi, A. Laalam, University of North Dakota; A. Hassan, King Fahd University of Petroleum & Minerals; et. al.
Numerical Investigation of Fishbone Well Design Impact on Geothermal System Enhancement in North Dakota by H. Ouadi, A. Laalam, M. Alamooti, University of North Dakota, et. al.
Applications of Underbalanced Fishbone Drilling for Improved Recovery and Reduced Carbon Footprint in Unconventional Plays by H. Ouadi, S. Mishani, V. Rasouli, University of North Dakota.
SPE 155958 Fishbone Well Drilling and Completion Technology in Ultra-Thin Reservoir by G. Xing, F. Guo, C. Song, Daqing Oilfield Limited Company; et. al.
