fax 01-972-952-9435. AbstractThis report summarizes the testing and field application of a rotary liner drilling system. Liner drilling was first attempted by Amoco Norway Oil Company (ANC)C) in 1993 and there have since been eight additional wells drilled using rotary, motor, and a combination rotary/motor liner drilling system. This paper will focus on six of those wells drilled with a rotary liner drilling system.Key learnings from these well applications in the Norwegian sector of the North Sea are reviewed.

Traditional well designs for high angle and extended-reach wells often mandate long 12¼" hole sections through the overburden. Effective hole cleaning and wellbore instability management are key technical challenges commonly associated with delivery of this section. However, despite the use of rotary steerable systems, which help promote good hole cleaning and minimise open hole exposure times, problematical trips out of hole are commonplace. The symptoms of tight hole are often associated with significant cuttings bed accumulations, use of packed assemblies or creep arising from swelling formations. In an attempt to improve overall drilling performance, a supersize hole strategy has been implemented to intentionally drill an enlarged hole through the overburden. At face value, this tactic seems to have as many disadvantages as advantages. However, practical experience of simultaneously drilling and underreaming 12¼"×13½" hole sections over a number of wells has resulted in overall efficiency improvements. The primary benefits associated with drilling an enlarged hole are ease of tripping-out drilling assemblies and more straightforward casing runs. Other advantages relate to lower downhole pressures or equivalent circulation density (ECD), decreased swab and surge pressures, and less string contact area. Disadvantages relate to increased hole cleaning requirements, additional tool failures as a result of higher vibration and a decreased rate of penetration (ROP). The paper discuss es various aspects of drilling and underreaming and contrasts results between enlarged and conventional hole sizes. Results from drilling both 12¼" and 12¼"×13½" hole sections in the Azeri-Chirag-Guneshli (ACG) fields in the Caspian Sea are reported. ROP (Rate of Penetration) and a new metric TTSW (Time To Secure Wellbore) are used to provide meaningful comparisons. Introduction The Caspian Sea includes an area of world class hydrocarbon accumulations. Reserve estimates for the ACG development are in excess of 5.4 billion barrels. Anticipated production rates are expected to exceed one million barrels per day by 2010. Hundreds of wells will be drilled from various platforms and semi-submersibles to exploit reserves across the structure. Having a cost effective well design strategy for the various well types will enhance both drilling performance and ultimate recovery of reserves. A significant number of these wells will be highly deviated or extended-reach in nature. Experience to date has shown that drilling and casing running through the overburden at high angle is particularly challenging. This is primarily due to interdependent problems arising from wellbore instability, hole cleaning and casing running. The paper will first provide an overview of operations on the first extended-reach wells drilled from the Chirag Platform. The discussion will then be extended to show how improvements to the basic well and casing design have helped to overcome problems in these early wells. The paper will then focus on more recent developments where field trials have explored the impact of purposefully drilling an enlarged hole section through the overburden. A comparison of the advantages and disadvantages of drilling an underreamed hole section will be given. The main differences hinge on managing hole cleaning, downhole vibration and performance. Each of these topics is examined in more detail where results from various field operations are used to illustrate various points. Finally, the paper addresses the issue of selecting the right hole size for underreaming and discusses options for future well designs. Chirag Field History The Chirag platform is located 120 km East of Baku in a water depth of 120m. The 24 slot jacket was installed in 1993 and first oil achieved in 1997. The initial drilling programme comprised 15 wells which were in close proximity to the platform. Early drilling operations were considered relatively trouble free; however in higher step-out wells just beyond 4 km, higher levels of non-productive time (NPT) were experienced.

Traditional well designs for high angle and extended-reach wells often mandate long 12¼" hole sections through the overburden. Effective hole cleaning and wellbore instability management are key technical challenges commonly associated with delivery of this section. However, despite the use of rotary steerable systems, which help promote good hole cleaning and minimise open hole exposure times, problematical trips out of hole are commonplace. The symptoms of tight hole are often associated with significant cuttings bed accumulations, use of packed assemblies or creep arising from swelling formations.In an attempt to improve overall drilling performance, a supersize hole strategy has been implemented to intentionally drill an enlarged hole through the overburden. At face value, this tactic seems to have as many disadvantages as advantages . However, practical experience of simultaneously drilling and underreaming 12¼ "×13½" hole sections over a number of wells has resulted in overall efficiency improvements.The primary benefits associated with drilling an enlarged hole are ease of tripping-out drilling assemblies and more straightforward casing runs. Other advantages relate to lower downhole pressures or equivalent circulation density (ECD), decreased swab and surge pressures , and less string contact area. Disadvantages relate to increased hole cleaning requirements, additional tool failures as a result of higher vibration and a decreased rate of penetration (ROP).The paper discuss es various aspects of drilling and underreaming and contrasts results between enlarged and conventional hole sizes. Results from drilling both 12¼" and 12¼"×13½" hole sections in the Azeri-Chirag-Guneshli (ACG) fields in the Caspian Sea are reported. ROP (Rate of Penetration) and a new metric TTSW ( Time To Secure Wellbore) are used to provide meaningful comparisons.

A downhole Splitter wellhead system was successfully introduced and field tested offshore in the Valhall Field, an upper Cretaceous chalk oil reservoir in the south end of the Norwegian sector of the North Sea (Figure 1) operated by Amoco Norway Oil Company on behalf of Amerada Hess Norge A/S, Elf Petroleum Norge A/S, and Enterprise Oil Norge Ltd. This is the first Splitter well in the North Sea area, and 3rd in the world. Extensive pre-planning and equipment function testing has been performed to meet the challenges posed by the application of this technology. The Splitter system is used in an innovative approach to drill, case and complete two independent wells in one wellhead housing. Each well can be operated, serviced and worked over as a complete separate unit. The 3 objectives with this project were:Test of new technology for possible better use of slots in a slot restrained environment.Explore near Valhall exploration area (Mjød Field)Provide a long term waste disposal solution for Valhall Due to hole stability problems, the second objective was canceled during the operation. Instead, a preplanned fallback production location on the Valhall field was drilled. Objectives 1 and 3 were successfully completed July 1997. One well is a 4700 m MD horizontal producer (850 m horizontal section) to the North of the Valhall Field. The second well is a high angle (68 deg) well with a long section of slim hole drilling prior to completion of a dedicated waste injection well, capable of taking roughly 4 MM bbls of waste at approximately 2200 m TVD in the overburden at the Valhall Field. Figure 2 shows a map of planned vs actual well locations. Introduction In January 1993 the Norwegian State Pollution Control Agency (SFT) reduced the allowable oil content on cuttings disposed to sea from 6% to 1%, a limit not achievable at the Valhall field with current technology, where there in addition to drilling waste also is generated large volumes of production waste (oily chalk and water). With cooperation from SFT, Amoco Norway and Amoco Production Research developed a unique through-tubing cuttings injection method in a dedicated injection well, capable of handling very large volumes of waste. This solution was successfully implemented at Valhall in January 1991. However, in the slot restrained environment at the Valhall platform, with a low-permeability reservoir, the cost for a non producing slot is high, and the Downhole Splitter wellhead system was identified as a potential way of optimizing slot use. The old waste injection well would be plugged and abandoned, the slot would be reclaimed, and a splitted slot installed. Another argument for implementing a new waste injection solution was the fact that the existing waste injection leg had several deformations in the wellbore above the reservoir, and there was some uncertainty with respect to future lifetime for this well. Mjød, an identified exploration opportunity some 4 kilometers south-east of the Valhall platform (Figure 2), had already been discarded due to too high dry hole cost. However, if the Splitter concept was used, a potential dry hole could be utilized for waste injection purposes. So although drilling the exploration well from an offset platform increased the drilling difficulties somewhat, it reduced the potential dry hole cost by as much as 90%.

fax 01-972-952-9435. AbstractThis report summarizes the testing and field application of a rotary liner drilling system. Liner drilling was first attempted by Amoco Norway Oil Company (ANC)C) in 1993 and there have since been eight additional wells drilled using rotary, motor, and a combination rotary/motor liner drilling system. This paper will focus on six of those wells drilled with a rotary liner drilling system.Key learnings from these well applications in the Norwegian sector of the North Sea are reviewed.