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.

Recent technological advances are driving casing and liner drilling from a niche market into the mainstream environment. Improved connections, tubulars, advances in rig technology and pipe handling have enabled operators to consider drilling with casing/liner as an option on many new wells 1,2 . Escalating deepwater costs and the need to further reduce onshore drilling expenses in low cost fields continue to push the technology forward.In a mature South Texas field, an operator discovered the difficulties of drilling into formations with weak matrix strengths, loss circulation zones, and tight pore pressure/fracture gradient windows.These issues have deemed the field sensitive to aggressive drilling techniques and the operator has been forced into a conservative drilling program with reduced flow rates and lower weight-on-bit capacity. The operator needed to reduce trouble time, lower costs and make the wells more economically feasible.A service company introduced a new liner drilling system solution to get through the extensive problematic zones. The system is engineered so the operator can ream to bottom and then continue drilling with the liner to the required target depth. The system is comprised of a drillable fixed cutter casing bit and a drill-in liner assembly designed to handle the rigors of a drilling environment (rotation, reciprocation and drilling torque). The liner system utilizes a running tool that allows the liner to be used in drilling mode handling all the required drilling loads without fear of release. Once at desired setting depth, the hydraulically balanced liner-running tool is released with a setting ball. The casing bit is manufactured from a specialized steel alloy that allows technicians to braze polycrystalline diamond compact (PDC) cutters directly to the one-piece bit ensuring a robust cutting structure capable of efficiently drilling new formation as well as reaming existing hole. The system allowed the operator to drill in the liner to TD, cement, and then drill out to the next casing point.To date, nine intervals have been drilled with this system in South Texas. This paper will focus on the problems encountered in the field, the development work in establishing a solution for the operator, the results attained, and lessons learned through using this new technology. TX 75083-3836, U.S.A., fax 1.972.952.9435.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIncreasingly, operators are looking for simple and effective methods to overcome the hazards and limitations imposed by depleted reservoirs, rubble zones or thief zones. One method is to utilize casing or liner drilling to isolate the problem area by combining drilling and casing in one operation. This can take on many forms from simple drill-in systems to full retrievable directional BHA's connected below the casing or liner string.A major independent operator has recently drilled two 12-1/4" hole sections in different wells to isolate a problem thief zone (Well A-2 BP01 and A-3). The drilling of one of these sections with liner (A-2 BP01) 1 and the other with casing (A-3) produced many operational and equipment learning that will increase efficiency in future applications. To drill the problem interval of the A3 well, the operator chose a tried and proven Casing Drive System, together with a new PDC casing bit 2 to drill down a full string of 9-5/8" casing.The choice of drilling with liner or casing is examined along with the equipment and operational practices required. Comparisons will be drawn with the offset well which was drilled conventionally and led to mud losses of over 3,000 barrels, the effectiveness of a smear or plastering effect while drilling with liner and casing is investigated.