ARCO Oil and Gas Company (ARCO) has operated jack-ups in the Gulf of Mexico (GOM) extensively over the last three decades. During this period, ARCO has drilled several hundred wells accumulating significant experience with a variety of different jack-ups.
In 1980, ARCO initiated a structural study to assess the risk of using jack-ups adjacent to fixed platforms. While the study was ongoing, a jack-up rig drilling an exploratory well for ARCO was destroyed during Hurricane Allen, further increasing interest in the subject. In the Spring of 1985, a work group of drilling, geotechnical, and marine engineers was assembled to review GOM jack-up operations and identify areas for improvement. As part of this effort, ARCO funded a compilation of GOM soil strength data, a key factor in jack-up design. The group also worked closely with a rig designer-builder to prepare a preliminary design for a new generation jack-up for GOM operations.
The purpose of this paper is to present some of the observations made as a result of this general operating experience and these detailed engineering studies. It is hoped that by promoting more discussion on GOM jack-up designs that the industry (rig designers and builders, drilling contractors, and petroleum operators) will begin design work toward the next generation GOM jack-up.
Two areas were studied in detail: Operating Efficiency and Structural Integrity. Evaluation of operating efficiency reveals relationships between rig designs and final operating costs. For example, drilling records show the cost of certain rig design limitations on drilling operations. Also, by reviewing new technology and benefits from its use, estimates can be made for drilling improvements from advanced rig capabilities.
Evaluation of structural integrity reveals the risk associated with failure of the unit during severe environmental loading. In the GOM, hurricanes are the environmental conditions of concern. Challenges exist both in accurately quantifying these storm conditions and consistently applying them to different offshore structures, i.e. MODU-A vs. MODU-B, MODU vs. a fixed platform.
This paper is focused towards GOM operations since it is a dominant petroleum region warranting specialized rig designs. The concept of an operations-based decision perspective for rig design applies globally however.
A survey of GOM jack-ups showed average rig age is 8 years, and only 7 of 185 rigs have been built in the last 3 years. With a useful average jack-up life of 12-15 years, there may be a shortage of good rigs in the near future. More important than calendar age is the "technical age" of the rigs. Although difficult to quantify exactly, the design, contracting, and construction process for jack-ups results in at least 2 to 3 years of lag time between technology and rig completion. For example, an 8 calendar year old rig, will be designed with technology that is 10 or 11 years old. This lag time on technology makes the above age distribution of great concern.
