| Abstract |
Obtaining drilling fluid and cutting returns in subnormal pressure regime is still a big challenge in the drilling industry. Aerated drilling has been introduced as one of the solution. Aerated Drilling is a technique where compressed air in combination with the drilling fluid is used to reduce the effective density of the fluid column in the wellbore. The main objective is to enhance the chance of having circulation during drilling by reducing the Equivalent Circulating Density (ECD). One of the main challenges in drilling a geothermal well is loss circulation. Typically, the well targets in geothermal drilling are faults, fractures or fissures that have high permeability and are connected with the geothermal reservoir which has subnormal pressure. When these faults or fractures are intersected, losses will occur as the drilling fluid will enter the fracture zone rather than flowing to surface. Some of the cutting may enter the encountered fracture zone but some may stay in the annulus and accumulate. This cutting accumulation will result in torque increase that will limit the capability to drill deeper and it will also increase the risk of stuck pipe due to cutting pack off. The cutting entering formation also becomes a later problem as it may reduce the permeability of the fracture and thus the production of the well. Having circulation is very beneficial as it will reduce the drilling risk, increase the drilling efficiency, enable better geological control, enable the formation evaluation from cutting samples, and minimize formation damage. Aerated drilling has been introduced to solve this problem. The intent is to manage the /ECD that will allow a full or partial circulation despite subnormal pressure zone has been penetrated, without neglecting the well control aspect of the well. Understanding the ECD under various air/mud ratios and understanding the geothermal formation pressure are essential for the successful application of the technology. This paper reviews the utilization of aerated drilling on several wells during the GPO-I 2012/2013 Salak Drilling Campaign, including the deepest geothermal well in Indonesia. The project planning, project execution, and the field result are discussed in this paper. Results show that the drilling efficiency has increased significantly in comparison to historical performance as indicated by extended bit life, longer hole section, higher ROP, and it allows deeper drilling. |