Same internal casing diameter from surface to TD

Lance Cook
CEO and President Enventure Global Technology

Expandable tubular technology is quickly gaining industry recognition as a break-through that is allowing operators to drill deeper while decreasing well construc-tion costs and increasing production rates. Currently, only the top quarter of the earth's crust has been explored, but new technology will soon allow the industry to explore the three remaining quarters in search of new reserves.

The ultimate objective of the MonoDiameter System, the next generation of solid expandable tubular (SET) technology that Enventure Global Technology and Shell are developing, is to make possible a well with the same internal casing diameter from surface to total depth. This system will save significant amounts of time and money by reducing flat time during drilling operations, using a smaller BOP stack, and standardizing equipment such as drillstrings and bits as well as casing. Safety will be enhanced because rig crews will not have to handle large diameter casing and drilling equipment, and the frequency of changing out drilling equipment and bottomhole assemblies will be minimized. Smaller, less expensive rigs can be used, helping to dramatically reduce daily rig costs.

A well drilled using this system will have no diameter loss with each new liner. This means that regardless of unexpected reservoir challenges, each well drilled can potentially reach its reservoir with a casing size that will enable reservoirs to produce at full potential.

Using less expensive offshore rigs

Being able to use smaller, earlier generation semisubmersibles and drillships is one of the key reasons to drill wells with this system. Today, an operator drilling in ultra-deepwater with a state-of-the-art drillship could be spending several hundred thousand dollars daily in spread costs. Huge drillships are necessary to accommodate nearly 10,000 ft of large-diameter riser, huge casing sizes, and massive BOP stacks. The rig must have enough deckload to handle not only a working drilling fluid capacity, but also a riser displacement capacity should there be a situation that requires disconnecting the riser.

However, with a 9 5/8-in. well drilled using this system, the riser and BOP stack can be downsized, meaning the deck space to store the riser and BOP stack can be smaller. Less drilling fluid is required for the smaller riser, so the mud displacement and storage capacity can be smaller. With downsized equipment requirements, the displacement of the drilling rig also can be decreased. All this can result in greatly reduced mobilization time from location to location, dropping fuel expenses.

Plans have been initiated for converting a third-generation drillship for use with SETs in ultra-deepwater settings to replace the fifth-generation ships currently in use. This conversion can realize an estimated potential savings of $20 million per ultra-deepwater well.

Standardized equipment

Wells of this nature could result in standardization of equipment and downhole tubulars. With standardization would come a significant reduction in the cost of drilling a well. Single drillstring and bit sizes would be used throughout the entire well. Automated drilling systems would be more efficient if they didn't need to be variable for a large range of tubular sizes. Other equipment that is variable to accommodate different sizes also could be made more efficient and reliable.

There also will be standardization of tubing sizes for these wells. An initial survey indicated most operators want 6 1/2-in. or 8 1/2-in. completions, with the industry standard- izing on these two sizes plus perhaps a third smaller size. The result would be to standardize the pipe sizes for these completions. Since a large part of the cost of running a pipe mill is shutting down to change rollers for different pipe sizes, the mills could run at higher capacity and reduce the cost of tubulars at the same time. Consequently, the cost of drilling and completing a well would drop dramatically.

The wells would need only certain size bits and certain size wellheads, resulting in a global standardization. The inventory requirements would drop substantially, and waste would be minimized to a point that affects profits.

Protecting the environment

An additional benefit of SET technology is the improved environmental protection it will bring to the industry. The three primary benefits to the environment are:

* Reducing rig sizes will shrink operational footprints and generate fewer emissions

*Producing less waste because smaller wells use up to 50% less drilling mud and produce 50% fewer cuttings

*Requiring fewer wells to recover the same amount of hydrocarbons by allowing oper-ators to flow wells at maximum rates and drill multiple wells from a common platform.

Another dramatic impact is the ability to add one 9 5/8-in. casing string after another, like Lego pieces, eliminating the main barrier to reaching dramatically deeper depths.

For example, a well drilled with a pre-expanded external diameter of 9 5/8-in. can demonstrate all of the benefits of the technology. After an expansion, the casing has an internal diameter of 10 1/3-in. in each consecutive liner. The constant internal diameter will allow operators to use larger and stronger equipment and larger, more accurate logging instruments than are currently practical at great depths.

This well will also use half the steel that a conventional well plan would call for, generate half the cuttings, require half the amount of consumables, and allow drilling from a smaller rig. It will require fewer sizes of casing, produce at higher rates, and bring the operator dramatic savings with the decrease in day rates and the number of days it will take to drill.

Additionally, the well will reduce the impact on the environment and will be able to reach reserves that were previously considered uneconomic or out of reach, which can help secure the energy supplies needed to maintain global economic expansion.

This system will be particularly useful in deepwater and for deep wells where unexpected challenges are commonly encountered before reaching the desired target depth. Combining the effects of reducing the amount of materials used, such as mud and steel, and decreasing drilling waste generated by 50% results in a process that will do for well construction what 3D seismic did for geologic exploration and hydrocarbon development.

Current status

The first downhole prototype will be run in a well in South Texas this summer. The field test will be conducted in the less expensive onshore environment, but it is expected that the system will be ready for commercial use by 4Q 2002.

This system will be fully realized when the technique of expanding thick-wall (high-collapse) casing with gas-tight connectors is completed. Development of this expanding technology is currently under way. Thick-wall solid tubulars have been expanded in the lab and in surface tests, as have gas-tight connectors. A conservative time estimate for completion of a quality system is 2007.

The technology used to develop this quantum leap in drilling new wells is the first major improvement in the oil and gas industry in years that was not imported from the computer or aerospace industries. It will fundamentally change the way wells will be drilled in the future. These radical changes encompass issues from saving time and reducing drilling costs to decreasing the environmental disturbance during production.