Publications

Underbalanced drilling (UBD) techniques are evolving as oil companies learn how to use the technology to maximize well production and to reduce the company costs. The economic cost of exploration and production (E&P) continue to encourage the use of new methods to reduce problems and costs. UBD technology is one of such methods that is offering effective solution to conventional drilling problems. UBD is a procedure used intentionally to drill oil and gas wells where the equivalent circulating density (ECD) of the drilling fluid is less than the pore pressure in the formation being drilled. Therefore, the well is flowing at the same its drilling. UBD techniques had not been introduced until Kangean Energy Indonesia (KEI) experienced high amount of lost circulation while drilling the exploration well in Sepanjang field. The reason for using the UBD on this field was depleted production and KEI experienced some mud losses case. UBD process on this well falls into two major categories goals. The first goal is to reduce the formation damage, because this technique gives benefit for minimizing the damage caused by invasion of drilling fluid into the formation and the second one to increase the ROP. Other additional benefits are reduced drilling time, increased bit life, early detection production zone and dynamic testing of productive zone while drilling. The UBD application on this field is using one phase under balanced flow modeling, with diesel as the drilling fluid. In this study we also compared the performance of other type of drilling fluids such as brine water, fresh water and gasified liquid as the flow performance under UBD condition for comparison. The drill pipe injection technique was proposed in this well because it fit with the well conditions where drilling was not expected to through the gas cap and the well will be completed in 8 ½ inch open hole. This paper discusses the UBD design parameters especially cutting transport parameters in 8 ½ inch horizontal UBD operation. We investigated the influence or the effect the variety of hole size, Bottom Hole assembly (BHA) tool size, cutting size, pipe rotation, penetration rate, variety of injection pump rate, and the use of drilling fluids on cutting transport efficiency using the concept of Minimum Transport Velocity (MTV) from Larsen and Rudi-Sindhu correlations. This concept assumes that a hole can be cleaned efficiently by maintaining the cutting transport parameters, if the annular velocity (Vann) is equal to or greater than a minimum transport velocity (Vmin) for operational condition. So, the lower the minimum transport velocity is, the easier it is to efficiently clean the hole.