Objectives/Scope Historically, deepwater drilling riser challenges were always seen to be related to riser weight and metocean stresses. Consideration of the riser as a pressure vessel has been limited to production riser applications or smaller high pressure risers used for floating surface BOP drilling. In single gradient drilling, the riser sees pressure differentials of 3000PSI or even more in the lowest regions. A failure of the riser will create an underbalanced situation, which could result in a release of hydrocarbons to the environment. In the lower part of the riser, there is very little difference between riser stresses for conventional and managed pressure drilling applications. In the upper part, the slightly higher pressure during back pressure MPD may even help with tensile stress performance of the riser. This understanding of the riser function should also change the perception of what really is the primary barrier in deepwater drilling, where the riser and the DP system should be considered as the key primary barrier elements, holding the overbalanced fluid column. Considering the conventional drilling riser a pressure vessel, the authors look at recommended and regulatory requirements for riser integrity assurance, and find them not satisfactory for todays uses of the riser, which is another example of the "mission creep" that occurred in our industry, drilling in ever deeper waters, without changing the operating principles for floating drilling originally developed for areas just outside the reach of the jackup. Aside from offshore physical inspections every five years, no insitu method for riser integrity inspection exists at this time. The authors propose a new method for inspecting the integrity of the riser, based on ultrasonic inspection technology, which has become a vital element in pipeline integrity management. Basically, pipelines are pressure vessels which are located close under the surface and extending at great length through environmentally sensitive and often densely populated areas. To assure the integrity and safe operation of these gas and liquid systems, PHMSA (Pipeline and Hazardous Materials Safety Administration) requires these pipelines to be inspected on a regular basis for Wall Loss and Crack Detection. Internal In Line Ultrasonic Crack and Wall Thickness Inspection Systems are providing highly detailed information on the integrity of the pipeline and have become the most widely accepted and accurate technology used to assure the continuous and safe operation of pipeline systems worldwide. The Offshore Riser Inspection Systems (ORIS) has adapted this highly efficient and well proven technology to the offshore industry, providing a clean and detailed bill of health through regular, non-disruptive and insitu inspection of the marine riser system. The ORIS ultrasonic sensor carrier, controlled by a wire-line logging unit, will provide high quality digital data, through real-time surface read-out and on-site interpretation, while allowing for substantial savings when compared to standard surface inspection methods.

Aerated mud is now a proven technique for drilling lost circulation zones in ADCO's fields. Severe lost circulation problems encountered while drilling surface aquifer formations were traditionally cured by using oil to lighten water based mud. Aerated drilling is one method that eliminates any environmental impact of discharging oil to the desert. As a pilot, four wells were drilled in Abu Dhabi Onshore field utilizing aerated mud. All proved to be operationally successful achieving the goal of drilling without using crude oil to lighten the mud. The extra cost of the air compressors was offset by eliminating crude oil and waste treatment cost. Air drilling time was reduced 16% by the 4th well, but further improvement in bit hydraulics is required to increase penetration rates. The original air package design was to deliver 1500 SCFM of air at 1350 psi. A booster to increase the air discharge pressure to 1900 psi was employed for the last three wells. This increased the hydraulic energy delivered to the bit. Using greater air compression capacity with optimized bit nozzles played the key role in improving bottom hole cleaning and increasing the rate of penetration. Introduction Historically the surface hole section was drilled with water based mud lightened to 56 pcf with crude oil additions to prevent losses. Environmental concerns and economic considerations for crude oil consumption and waste pit clean-up promoted the search for a means of improving drilling conditions for the 17.1/2" surface hole by:-Replacing the oil/water mud mixture with aerated mud and thus controlling losses throughout the 17.1/2" hole section.Improving the drillability of hard limestone formations by reducing hydrostatic overbalance pressure. Engineering Studies indicated one solution to the loss circulation problem lay in the use of aerated mud drilling. It was obvious from the beginning that straight air drilling or foam drilling was not practical because of high potential water flows from the aquifer zones that had to be penetrated. Blind drilling was not economically feasible in the desert operation. Fluid pumping rates of 850 to 950 GPM are normally used to drill and clean the 17.1/2" hole. Blind drilling requires about 25,000 to 30,000 BWPD for about six days assuming complete losses. Three shallow water supply wells are normally drilled for each location. These wells produce a total 5000 BWPD on average. The balance of 20,000 to 25,000 BWPD required for blind drilling must be hauled by trucks or produced by drilling additional water supply wells, both of which are expensive. Furthermore, known problems associated with blind drilling such as frequent drill string twist-offs limit the acceptance of blind drilling. Aerated mud was seen as an operational, economical and environmentally friendly solution to combat massive mud losses into the three separate water source aquifers at 1400, 2800 and 4500 feet. Using aerated mud made drilling through these low pressure, water-bearing reservoirs with full returns to the surface possible. Air injection through the stand pipe is the simplest way of lowering the density of the drilling fluid.

Casing-while-drilling is a relatively new well construction process or technology for simultaneously drilling and casing a wellbore, and has been utilized globally over the last 15 years or so. This technology has shown advantages of reducing overall drilling time and cost. It has demonstrated signs of reducing hole problems, such as mud losses, through plastering effect because of the rotation of the casing string against the formation. It provides assurance to case off unstable formations while drilling, resulting in significantly reduced well construction costs. Saudi Aramco has made several field test runs of this technology beginning in early October 2008, including deployments of both simple casing drilling with drill-through casing bit (non-retrievable) system and advanced bottom hole assembly (BHA) retrievable system designed for directional casing drilling. This paper will document the lessons learned from implementation of the technology, including planning and design, rig operations, problems encountered, modifications made to reduce risk after extensive review and investigation, and finally, successful deployment of a directional casing drilling to the planned casing point with a 17" x 13-⅜" system. In addition, the paper briefly outlines the further required improvements of casing drilling tools to ensure continued success in the future.

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