Application of Tunnelling Technology to the HDD Sector for Full Loss of Drilling Returns Crossings

Abstract

This submission will detail the customisation and innovation associated with utilising a modified tunnelling mixing system for HDD applications where full drilling losses were predicted. It outlines the process from concept design through to testing and implementation throughout the Jansz IO HDD Project. Three 36-inch 600m crossings were drilled in highly fractured ground, leading to complete losses from MD60 to MD600. Given the constraints associated with working in a Class A Nature Reserve, saltwater bio-degradable drilling fluids were required. This required a mixture of two polymers (Xanthan & Guar) and 3 additives (Soda Ash, Defoamer & Biocide) to be mixed at high volumes with predictable and repeatable compositions. The project team consulted with suppliers of a tunnelling mixing system and composed a customised solution to modify tunnelling technologies for the HDD industry These modifications were field tested in Italy to ensure the system was suitable for use on the critical project. The resulting outcome was a mixing system capable of high volumes (2x 100kL / hour systems) with +/- 1kg accuracy on additives using load cells on dosing. Additionally, through augured loading of polymers, the requirement for manual handling was eliminated, along with the risk of spills and environmental contamination. This solution can now be utilised on upcoming major projects in the Australasian market and demonstrates a solution for the HDD industry for drilling with full losses. Additionally, it highlights the capability for increased crossover within the trenchless industry for collaboration on unique and challenging problems. 1 No-Dig Down Under 2025 Application of Tunnelling Technology to the HDD Sector for Full Loss of Drilling Returns Crossings Stuart-Robertson, John 1. PREAMBLE Horizontal Directional Drilling (HDD) operations can incur significant cost impacts when drilling fluid is lost to the formation, a condition known as inadvertent returns or lost circulation. Drilling fluid, typically composed of bentonite and water or other additives, plays a critical role in lubricating the drill bit, stabilizing the borehole, and removing cuttings. When the fluid escapes into porous or fractured formations, it not only increases the cost of replacing lost fluid but also disrupts the efficiency of the drilling process. When fluid losses occur and replacement fluid is not mixed and pumped promptly, downhole conditions can deteriorate quickly resulting in stuck pipe, increased torque, or borehole collapse. This reactive approach often forces crews into unplanned shutdowns while waiting for new fluid volumes to be prepared, wasting labour hours and leaving expensive equipment idle. In some cases, the delay can also require more complex and costly remediation efforts such as the use of specialty loss circulation materials or re-drilling sections of the bore. These time and material costs, combined with potential schedule overruns and penalties, highlight the importance of having adequate mixing capacity and contingency planning to ensure continuous operations during fluid loss events. Therefore, careful planning, real-time monitoring, and proactive mitigation strategies are essential to control the financial risks associated with fluid loss in HDD operations. 2. PROJECT The Jansz IO Compression (JIC) Project is being undertaken by Chevron as operator of the Greater Gorgon development on behalf of the joint venture participants. The Jansz-Io field is located approximately 130km northwest of Barrow Island in water depths of approximately 1350m and supplies gas to the Gorgon LNG plant on Barrow Island. The JIC project is a life extension activity that will provide compression to the Jansz-Io field to maintain plateau gas supply to the Liquefied Natural Gas (LNG) plant and maximize recovery from the reservoir. Error! Reference source not found. Location of Barrow Island relative to the Gorgon and Jansz gas fields. Spiecapag Australia, trading as HDI Lucas, were awarded the landfall HDD works to facilitate the onshore to offshore transition of the power and communications cables from the offshore floating field control station back to the LNG plant onshore. The scope of works involved the trenchless installation of: • 3 x 600m crossings for DN630 HDPE conduits, • Under strict environmental controls due to the island’s classification as a Class A Nature Reserve. 3. PROJECT ENVIRONMENTAL CONSTRAINTS Chevron is permitted to operate on Barrow Island, a Class A Nature Reserve under strict environmental conditions and legislative frameworks. This highly sensitive arrangement is unique in Australia, and possibly the world, given that Barrow Island is both one of Australia’s most important conservation areas, home to rare and endemic species,

Techniques