Design and Installation of a Subsea Multiwell Drilling Template at Garden Banks Block 189
Authors: Domangue R.J. 
Published: October 2008

The cost effective philosophy of a drilling template has been applied to the development of Garden Banks 189 in the Gulf of Mexico. This paper describes the economics, design and installation of a simple drilling template for multiple sub sea exploratory/delineation wells.

Methods to costs have operators. prior to program is reduce project development always been of interest to One of the methods employed completing the delineation the drilling template concept.

An operator can drill multiple delineation wells through a drilling template to investigate a prospect. A template provides a means to accurately space-out future wells in relation to each other. If the prospect is commercial, a production facility (typically a platform) can be aligned and installed over the predrilled wells.

These wells can be tied back to the surface and used as production wells. Savings are achieved in this development scheme because there are no expendable wells.

Although attractive, the first prerequisite for a drilling template application is that the template site must be a suitable platform site.

Typically, this location is not known after one exploratory well. Two or more delineation wells are normally required to pinpoint this location. For this reason, Texaco and other companies have not routinely benefited from this concept.

In May 1989, a nine slot template was installed over the #1 discovery well in 718' of water at Garden Banks 189. Due to the circumstances, a unique template design and an unconventional installation procedure resulted. Since installation, two delineation wells have been drilled through the template and temporarily abandoned. Tiebacks of these 3 wells are scheduled immediately following the installation of the platform in 1991.

PROJECT HISTORY

In the fall of 1988, Texaco drilled one successful sub sea exploratory well in 718' of water at Garden Banks 189 (9B 189). Geographically, this block 1S located in the Gulf of Mexico 185 miles southeast of Houston, Texas.

The straight hole #1 discovery well penetrated 169' of oil and 126' of gas pay from six intervals ranging from 5000' to 8500' TVD. Two of the oil zones were flow tested at 739 and 2037 BOPD respectively.

The #1 well was drilled through a seismic bright-spot associated area in the southwest quadrant of GB 189 (Figure 1). This well is positioned 1200' south of an east/west shipping fairway which obstructs the entire northern half of the block. The southeast and southwest quadrants are geologically separated by a salt diaper. Severe seafloor irregularities exist throughout the south central region of the block over the salt diaper.

Potential platform sites were limited to the southwest quadrant due to the confinements imposed by the fairway, seafloor irregularities, salt diaper, reserve locations and lease lines. The #1 well's location offered a suitable platform location based on preliminary mapping, the #l's results, a shallow hazard study and a drilling reach study.

This site was operationally suitable because it permitted future platform wells to fully exploit the discovered bright-spot region and also allowed the capability of reaching into a potential wildcat bright-spot region to the northeast.