Shallow Gas Well Drilling with Coiled Tubing in the San Juan Basin
Authors: Moon Robert G. , Ovitz Robert W. , Guild G. John , Biggs Michael D. 
Published: December 2007

Coiled tubing is being utilized to drill new wells, for re-entry drilling to deepen or laterally extend existing wells, and for underbalanced drilling to prevent formation damage. Less than a decade old, coiled tubing drilling technology is still in its inaugural development stage. Initially, utilizing coiled tubing was viewed as a "science project" to determine the validity of performing drilling operations in-lieu of the conventional rotary rig. Like any new technology, the initial attempts were not always successful, but did show promise as an economical alternative if continued efforts were made in the refinement of equipment and operational procedures. A multiwell project has been completed in the San Juan Basin of Northwestern New Mexico which provides documentation indicating that coiled tubing can be an alternative to the conventional rotary rig. A 3-well pilot project was first completed utilizing the resources of a coiled tubing service company and a producing company. After post-review of the 3-well pilot project, a 6-well project was completed uniquely utilizing the combined resources of a coiled tubing service company, a producing company, and a drilling contractor. This combination of resources aided in the refinement of surface equipment, personnel, mud systems, jointed pipe handling, and mobilization. The results of the project indicate that utilization of coiled tubing for the specific wells drilled was an economical alternative to the conventional rotary rig for drilling shallow gas wells.

Introduction

The total depth of the wells to be drilled in the San Juan Basin ranged from 1500' to 2400'. The producing intervals targeted were a normal to sub-normal pressured sandstone formation and a normal pressured coal formation. The casing program for these wells includes surface casing set to 250' and production casing set 50-100' below the targeted producing formation (Fig. 1). After production casing is set, the wells are perforated and hydraulically fractured. Completion is finalized with well flowback and suspension of packerless production tubing. The drilling process can be performed with a moderate depth conventional rotary rig in approximately 3 days. This includes mobilization, setting surface casing, setting production casing, logging, and de-mobilization.

The first step in the drilling and completion of these wells was the installation of surface casing. For this program, a workover rig was brought in to drill surface hole and to install the surface casing. It was concluded that this was the most efficient method due to the limited jointed pipe handling capacity of the coiled tubing unit used during this program. After the workover rig was moved off location, the coiled tubing unit was brought in to drill production hole out of the surface casing to total well depth. Again, with the limited jointed pipe handling capabilities of the coiled tubing unit, a workover rig was moved in to install the production casing after the coiled tubing unit was moved off location.

Economic Considerations

With the multiple move in and move out operations, coiled tubing may not appear to be the most efficient method for drilling these wells. Others factors have to be taken into consideration to realize true economical benefit. Unlike the conventional rotary rig, mobilization cost is minimized with the workover rig and the coiled tubing unit. They are both truck or trailer mounted, with their support equipment, and require minimal time to move in and move out. Because they require less space than the conventional rotary rig, both the workover rig and coiled tubing unit require smaller locations. This reduces location preparation cost and surface damage. If available, as was the case for the these wells, existing well locations required little preparation to provide sufficient space for drilling operations. Drilling next to offset wells to avoid logging was also an economic benefit for these wells. P. 469