TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOperators are always looking for ways to reduce risk in high cost environments and maximize value. Many challenges exist in the drilling environment today including depleted sands, lost circulation zones, weak formations and rubble zones. Casing and liner drilling has found its way from a niche market into the mainstream drilling environment through recent successes in a variety of these applications. There exist several options to drilling down casing or liners. These include retrievable BHA's with traditional measurement and logging equipment and non-retrievable BHA's that are drilled or reamed into place and cemented. This paper presents several case studies where non-retrievable casing/liner drilling technology has either improved the economics of a challenging application or made the application technically viable. These applications vary from onshore wells with tight fracture gradient schemes, shallow onshore wells looking to improve economics in surface hole intervals to offshore wells reducing risk by drilling or reaming down casing and liner strings. Applications will be taken from the Gulf of Mexico, South Texas, West Africa, Australia and Norway. The justification of using casing/liner drilling technology on these wells will be explored, as well as the lessons learned to apply to future drilling programs.

One of the many challenges for the industry is how to extend the limits from rig capacities without significantly increasing cost; this is a perpetual problem which will continue to challenge the industry as the perceived norms for well designs are driven forward, with the need to tap into ever deeper and more distant targets. A way to address this challenge is to use a lighter drill string. The objective of this investigation was to determine whether, by reducing string weight and changing the material properties of the drill string it is possible to extend the operational envelope of the drilling rig; without having a detrimental impact on the drilling process. A field testing program was carried out on a full-scale experimental drilling rig in Oklahoma, USA. To test this hypothesis, steel drill pipe (SDP) was exchanged for aluminum drill pipe (ADP). By utilizing this methodology, it is possible to greatly reduce the weight of the drill string without significantly reducing its mechanical integrity. Two representative, well-known geological sections on separate wells were drilled with a string containing ADP. Extensive surface and downhole datasets were obtained on these wells. Dynamic drilling data was recorded at three discrete points along the drill string. At two of these three points, mechanical drilling data was also collected. An advanced modeling package was used during the planning phase of these wells and during the post-drilling analysis of the datasets. Through interpretation of the results from the testing program and by extensive modeling, it was possible to extrapolate the extent to which the operating envelope may be extended. These models were then used to challenge Extended Reach Drilling (ERD) profiles and investigate if the drilling envelope could be extended by applying ADP to future projects.