Casing Drilling Activity Expands in South Texas

Abstract

Abstract Conoco has had a sustained, multi-rig, development program in the Lobo field of South Texas since the mid-1990's. Drilling efficiency using conventional techniques has improved to the point where additional gains are difficult to achieve. Drilling with casing was implemented as a potential way to provide a step change to drilling performance in this mature field. The Casing Drilling* process has proven to significantly reduce the in-hole trouble time below the low value that was already obtained and has demonstrated the ability to further reduce drilling costs. The first two phases of the Lobo Casing Drilling program were conducted with a dual-purpose (Casing Drilling/conventional drilling) rig. After drilling 22 wells, the Lobo Casing Drilling program is being expanded by replacing this rig with three new Casing Drilling rigs designed to further optimize Casing Drilling performance. The first of these rigs is on location and the other two will begin operations by the end of 2002. Introduction Conoco produces about 520 MMCFD of natural gas from the Lobo trend in South Texas and has had a sustained, multi-rig, development program there since 1997. At that time an active field development program was initiated with the goal of drilling about 1000 wells in seven years. This program was built upon many technology improvements introduced in the previous years of Lobo drilling, while others were spawned in the early years of the renewed field development program.1,2,3,4,5 By 2001, ten rigs were being employed to drill about 160 wells per year, but the drilling efficiency was stagnated with an average 10,500 ft well taking about 19.2 days from spud to rig release. Drilling efficiency using conventional techniques had been improved to the point where additional gains were difficult to achieve. Each hole section was drilled in a single run with a PDC bit and downhole trouble time had been reduced to less than 10% of the overall drilling time. Even with the high ROP's and minimized trouble time, further cost reduction was dictated by the need to develop smaller reservoirs. It became clear that a new approach was needed to provide any chance of achieving significant well cost reduction. A specific goal was adopted to reduce drilling costs sufficiently to make reservoirs smaller than 1.0 BCF economical. The ability to develop reservoirs this size would extend the development potential for several years as the untapped reservoir size becomes smaller and smaller in the highly faulted Lobo field. In examining the wells and drilling performance it was obvious that great strides had been made in increasing ROP, drilling each hole section with a single bit, and in improving general rig operation efficiency. The most significant thing that still limited the ability to reduce days on each well was the time to prevent and recover from downhole problems and the flat time at the TD of each hole section. Stuck pipe and lost circulation are the most consistent contributors to the trouble events for Lobo wells. These two items accounted for about 75% of the trouble time in 2000 and 2001 (Figure 1), while well control and a failure to successfully run the 7" casing were also significant in 2001 and 2000, respectfully.6 Drilling with casing was identified in early 2001 as a technology that could potentially solve these problems and provide a step change in drilling performance in the mature Lobo field. Tesco's Casing Drilling system was selected to evaluate the potential impact of drilling with casing on Lobo drilling economics.