The Challenge of Drilling in Highly Overpressure Area – A Geomechanical Implication



The Lengowangi field, located onshore East Java, Indonesia was discovered in 2006. The main challenges in this area are the over-pressured Lower Ngrayong and Tuban formations. The first well L1 was successfully drilled in 2006 with current gas production up to 10 MMCFD. The second well L2 was drilled up-dip in 2009 but could not reach the target because of well control issues related to high pore pressure. Well was TD’d about 2800ft MD shorter than planned depth. Third well L3 is drilled as twin well near L2. To optimize drilling in this challenging field, a detail geomechanical evaluation study was conducted. The study utilized the drilling and log data gathered in L1 and L2 and aimed to establish the cause of overpressure and define the pore pressure profile of the  field. The study concludes that significant overpressure exists in Lengowangi field. Subsequently, a Mechanical Earth Model was constructed for L3 and safe and stable mud weight windows were
established. L3 was spud in early 2010 and study recommendations were taken into account for well designing and drilling. Post-drill analysis of L3 shows that pore pressure matched with the upper limit of the pre-drill pore pressure estimate. The highest pore pressure estimated is 17.1ppg near the well bottom. For drilling further, mud weight could not be increased to recommended value of 17.4ppg due to drilling restrictions. Hence, some flows and connection gas were observed due to low overbalance. Drilling is considered a success as well is TD’d close to plan TD with improved borehole stability compared to L1 and L2. Mechanical Earth Model constructed for Lengowangi field will now be used for optimizing upcoming drilling activities in the field by improving borehole stability, defining the pore pressure profile and by establishing the safe and stable mud weight windows.


Authors : M. Khawadja Kamaluddin, Andi M. Adiwiarta