Collaborative BHA Design Optimization Modeling Leads to a Successful Run in a Challenging Formation

Abstract

An oil and gas operator in Indonesia had a second exploration well (L-2) in the L field located in Seram Island of eastern Indonesia. This field is known for its extremely harsh drilling environment. One of the challenging parts is the overpressured carbonate formation, which was planned to be drilled in the 8½-in section with 17-lbm/galUS water-base mud (WBM) mud density. Based on the experience in the previous well (L-1) and looking at the challenges that could potentially happen in L-2, good prejob planning is required to improve the drilling performance. A collaborative modeling job was performed—involving well trajectory design, BHA design optimization, hydraulics modeling, and torque and drag modeling—which utilized static simulation as well as drillstring vibrations modeling utilizing finite element analysis (FEA) dynamic simulation. This collaborative modeling greatly improved the bit and bottom hole assembly (BHA) selection capability by eliminating the uncertainty. Additionally, the dynamics simulation was also capable of generating a stable drilling parameters roadmap as a guideline for the driller and directional driller onsite. Several drill bits and BHA options were modeled and simulated under different drilling conditions to determine the most stable configuration. The result shows that the combination of point-the-bit rotary steerable system (RSS) and a seven-blade, 16-mm-cutter bit is the optimal BHA in the 8½-in section to drill through the hard and overpressured carbonate interval within a certain stable drilling parameters window. The result was satisfactory where the bit-BHA-parameters combination successfully delivered the service for drilling the 2,780-ft interval in 12 fewer days than the expected drilling time (as per AFE with motor BHA), drilling 18 days faster than the previous 8½-in section in L-1 well, and reduced the number of BHA runs by 50%. Such performance was translated into 18 days spread cost saving (USD 2,673,000) for the operator as compared with the previous well, and 12 days cost saving (USD 1,782,000) as compared with AFE days.