As the oil and gas industry matures, so does its technology and equipment. As a drilling rig gets older, it becomes increasingly challenging to use it to explore for untapped deep reserves. Offshore rig builders are constantly manufacturing rigs with new, sophisticated capabilities, thereby widening the technology gap between the new rigs and the aging ones. As a result, many operators of older rigs are modifying their rigs to compete with newer ones. Using a modified second-generation semi-submersible rig in Indonesia, Total was able to reach target depth in an ultra-deepwater well by deploying a combination of surface stack drilling technology, a subsea shut-off device known as an environmental safe guard (ESG), and solid expandable tubular technology. If conventional casing had been used, the optimal hole size at total depth (TD) would have been impossible to attain and economically unfeasible without the use of a fourth or fifth generation semi-submersible or drillship. This paper describes the safe and successful integration of new technologies that enable surface stack drilling with modified second- or third-generation semi-submersible rigs in environmentally less-benign areas, including the Gulf of Mexico. In addition, the paper will discuss the deployment of solid expandable tubular technology from a modified second-generation rig and show how this technology enabled the operator to achieve a sufficient hole size at total depth while maintaining an economically viable operation. Introduction It is rare to see innovative oilfield technology that gives renewed life to equipment that has been surpassed in size and capacity, but that is what the wedding of three new technologies is doing. The ESG is a means of closing a well and disconnecting if a riser failure occurs. It works as part of a system with the surface stack/riser system and certain second- and third-generation rigs. (It should be noted that not all second- and third-generation rigs can be outfitted for surface blowout preventer (BOP) operations.) Unocal Indonesia is a pioneer of surface stack drilling with second- and third-generation rigs in deep water, and they have been successfully using this method for some time. When adding the ESG device and solid expandable tubular technology to proven surface stack drilling technology, a synergy emerges. The combination of these three technologies enables an operator to drill a wellbore to TD in ultra-deep water that would have only been possible previously using a fourth- or fifth-generation rig. After several successful implementations, this combination of new technologies and smaller rigs is proving to be a reliable means of reducing drilling costs in ultra-deepwater locations. Surface BOP Operation Simply defined, surface BOP operation is the practice of utilizing a floating drilling unit fitted with a BOP that is suspended above the waterline in the moonpool area. The BOP, usually a land/jackup type BOP, is connected to a high-pressure riser serving as a conduit to the sea floor (Fig. 1). Typically, the high-pressure riser is 13–3/8 in. casing deployed in one continuous length from the casing shoe to the surface wellhead. The equipment configuration is similar to a jackup utilizing added top tension, with the exception the vessel is floating and the water depth may be thousands of feet deep. While Surface BOP drilling is not a new concept, the technology to take the concept into ultra deep water began about seven years ago offshore Indonesia1. The surface BOP concept for this program was initially deployed to drill inexpensive exploration wells in a benign environment in water depths between 100 and 500 ft. The operation was successful and proved that several days time could be saved compared to conventional subsea operations. The concept was further refined to go into deeper waters to utilize the same cost savings found in the relatively shallow water. The factors contributing to lower per-well costs in a relatively benign sea conditions include the following2:A mooring system using a taut wire type mooring can go into greater water depths than normal.A pre-laid mooring system significantly reduces the time required to move the drilling unit between locations.

This paper outlines the history of traditional offshore drilling with subsea Blowout Preventer (BOP) stacks and conventional riser and then illustrates the new method of surface stack drilling using the Environment Safe Guard (ESG). Introduction With the high cost of drilling in deepwater (greater than 2,500 feet/760 meters) and the limited number of available rigs with the capability of drilling in these water depths, a new approach to deepwater drilling was needed to try to reduce drilling costs to a more manageable level. As the water depth capability of new rigs increased, so have the costs. These high costs have resulted in many small, deepwater fields being rendered uneconomical to produce. In an effort to bring these fields back to economic viability, drillers have tried several ways to reduce their deep-water drilling costs. One of the most promising of these methods is to relocate the subsea BOP Stack to the surface and replace the large bore, low pressure drilling riser with conventional casing as the high pressure riser between the seabed and the rig. However, use of this method must be limited to the most benign sea state and weather conditions because of the risk of damage to the casing riser, which could result in environmental contamination. Surface Stack drilling has been successfully implemented in the south Pacific, but only during the summer months. In this area and under this weather window limitation, exploration drilling costs have been reduced by up to 35% with only a few emergencies arising. In order to continue and broaden the use of this proven cost saving drilling approach, a means of increasing the safety of the overall system, by reducing the risk in case of riser failure was required. If the riser could be sealed off at the seabed, the risk of riser failure could be completely eliminated. Also, if the riser could be disconnected just above the seabed sealing mechanism, overall rig safety could actually be increased beyond current levels. This is easily achieved using an assortment of existing, field proven components located on the seabed. Background The idea of locating a BOP Stack on the ocean surface to provide well control while drilling for offshore oil is not new. Figure 1, Typical Jack-up Rig When the first land rig was mounted on a barge decades ago, these systems were common. Later, Jack-up rigs (Figure 1) were outfitted with such systems. Jack-up rig evolution allowed their water depth capability to be expanded to 650 ft. Then, Semi-submersible rigs (Figure 2) and Drillships were developed and the BOPs were moved to the sea floor allowing a relatively low-pressure (and thus, less expensive) riser to transport the drilling mud returns back to the mud processing equipment located in the rig by way of the Riser annulus. This seabed BOP configuration facilitated the original water depth expansion to 1500 ft. with second generation rigs, and later to 3,000 ft. with third generation rigs.

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After the introduction of the Cameron 18-3/4" 20,000 psi EVO Drilling BOP at OTC, 2009, this paper will focus on identifying and completing the GAP technologies necessary for design and testing of a Deepwater 20,000 psi subsea BOP stack. This paper will identify design methodologies employed in design and testing of the BOP and outline GAP technologies that must be addressed for completing a Deepwater Subsea BOP stack. Taking a bottom up approach, the discussion will focus on the Wellhead connector and necessary loads, the Drill Through column, Choke and Kill systems and packaging to allow for use on existing rigs with minimal upgrade intervention.