Drilling for Coalbed Methane in the San Juan Basin With Coiled Tubing: Results, Learnings, and a World First

摘要

The San Juan basin is a prolific natural gas play in northwestern New Mexico and southwestern Colorado. It contains conventional oil and gas resources along with unconventional gas resources in the forms of tight gas and coalbed methane (CBM). Conventionally, drilling operations have been carried out by smaller rotary rigs with double or single derricks. These are usually minimalist, older rigs which fit well into the tight cost structure of the unconventional resources in the San Juan basin. In 2006, a coiled tubing drilling (CTD) pilot program was initiated in the San Juan basin consisting of seven wells, drilled in order of increasing complexity. The intention was to evaluate the full capabilities of CTD and its potential for use in the San Juan basin as well as the general U.S. onshore area. The drilling program included vertical wellbores, S-shaped wells off of a pad, and a horizontal sidetrack- all targeting the Fruitland Coal. In addition, several vertical and directional deep- set intermediate strings for future drilling of the deeper tight gas in the Mesa Verde and Dakota formations were set with CTD. The rig used was a new, custom-built, coiled tubing/rotary hybrid rig setup for use with large-diameter coiled tubing (3.5 in. and 2.875 in. OD). In addition, it had a single-sized derrick, rotary table and top-drive. This allowed the rig to drill with jointed pipe, handle and make-up bottomhole assemblies (BHA), and run liner and casing. Problems were encountered in areas such as fluid and additive selection, bit selection, hole stability issues, and crew training and rig limitations. In addition, CTD in this format was new to the San Juan basin and its personnel. Further issues that added difficulty included maintaining stringent standards of safety and environmental compliance, as well as conducting worldfirst operations such as running a rotary-steerable system (RSS) on coiled tubing. The end result was seven successfully drilled wells that are producing at the same or at better rates than offsets drilled with conventional rotary technology.