| Abstract |
The adaptation, analysis, and testing of new technologies are required to reduce well costs associated with deep Engineered Geothermal Systems (EGS). One of the advanced technologies already in use in the oil and gas industry that can be utilised to improve the economics of EGS is Controlled Pressure Drilling (CPD). CPD methods are an aggregation of techniques that utilise a closed and pressurised wellbore instead of the conventional practice of drilling with the hole open to the atmosphere. These methods utilise a Rotating Control Device (RCD) to close the well at surface, thereby allowing for greater and more precise control over the pressure profile of the well, which translates to more effective and efficient drilling operations. The three main types of CPD methods are Air Drilling (AD), Managed Pressure Drilling (MPD) and Under-Balanced Drilling (UBD). AD is mainly geared towards increasing the rate of penetration, MPD is for reducing rig non-performance time, while UBD is for minimising reservoir damage and increasing productivity. In Australia, all the CPD methods hold promise for greatly improving the economics of EGS projects. However, of the three CPD types, only UBD and MPD have so far been used to drill EGS systems in the country. AD methods, which according to studies have the potential to cut drilling costs by 15% to 20% by maximising the penetration rate, have not yet been utilised. Recent advances in AD technology have included the development of RCDs, air hammers, foam systems, and corrosion control chemicals that are able to withstand high temperatures and pressures, making them uniquely applicable to EGS systems. The varying nature and geology of the EGS systems in the country as well as the different approaches that have been taken by the companies pursuing their development, however, will require the customisation of CPD methods based on the applications required. This paper provides an introduction to CPD methods and a background as to how these methods have been used to improve drilling operations in other countries. It then narrows down its focus on the applicability of CPD methods in drilling EGS systems in Australia. It assesses the feasibility of utilising these methods in light of recent advances in CPD technology and provides how it can improve the economics of drilling EGS systems. Recommendations for the application of CPD methods in Australia are also provided. |