The Banuwati field offshore South East Sumatra, Indonesia presents major challenges to both drilling and liner running operations, because of the problematic Lower Baturaja limestone formation, which is a carbonate reef structure known for severe lost circulation conditions. The operator had previously experienced severe losses with wellbore stability issues while drilling this formation with the inability to set the 7-in. drilling liner at the planned depth in well A-3. The liner had to be pulled out of the hole leading to the eventual abandonment of the existing open hole section and resulted in the sidetracking of the well. Liner-while-drilling technology was identified as the most suitable solution for setting the planned 7-in. drilling liner through the loss interval because:○Documented lost circulation problems have been minimized or eliminated through the use of liner drilling technology possibly attributed to the "smear effect"1 phenomenon.○The liner system selected provided for high torsional capability as well as the requirement for both a mechanical and a pressure event to release the setting tool, thus minimizing the chances of premature release.○A drill shoe with a displaceable PDC cutting structure was used to drill the 8 1/2-in. hole section and subsequently displaced prior to cementing so as to allow drill out with a conventional drill bit and BHA.
This paper will discuss the implementation of liner drilling technology in the Banuwati field project. This technology was used to drill successfully through the known lost circulation zone with the 7-in. liner cemented in place allowing the operator to reach their completion objectives while realizing a savings of more than US$1 million.
Introduction
The Banuwati Field is located in the Java Sea some 40 miles off the east coast of Sumatra Island, and approximately 75 miles northeast of Jakarta, in 71 ft of water (See Fig. 1). Gas accumulation in the Banuwati area was not discovered until the late 1970s, even though there were exploration drillings as early as 1970. Banuwati-1, drilled in 1970, encountered oil in the Banuwati Formation but failed to reveal gas potential because the gas bearing Talang Akar intervals were faulted out in the well. Banuwati-2 was drilled in 1979 and discovered the Banuwati Gas Field, a major gas pool. The gas potential of this field was further confirmed through a full-scale delineation campaign during 1992–1993 consisting of the drilling of Banuwati-3, 4 and 5 and Martini-1, an up thrown fault block adjacent to the Banuwati Field.
Currently there are five producing gas wells in the field. Banuwati A-3 production comes from the 10,000–10,300' MD/5450' TVD Lower Batu Raja Limestone and Gita A Sand formations, where is original Banuwati -4 exploration well targets.(See Fig. 2). However, because the well track intersected a NW-SE fault twice, and also due to the presence of reactive shale formations, and in particular the lower Miocene Batu Raja limestone formation which is a zone of total lost circulation overlaying the productive Gita Sand, the drilling and completion of the wells has to overcome both well bore instability and total lost circulation challenges in one hole section. Conventional drilling methods and attempts to deal with the hole problems that existed in the A-3 well lead to extended well construction time resulting in three sidetracking operations, incurring costly non-productive time (NPT). In early 2007 during the drilling of the A-3 well, 9 5/8-in. casing was set at 8,487 ft MD. Attempts to drill an 8 1/2-in. section through the problem zones with the objective of setting a 7-in. liner to cover the Lower Baturaja lost circulation zone, where is the first pay zone interval, were unsuccessful. As a result the well was temporarily abandoned, while alternative methods of drilling through the trouble zones were considered.
