The Drilling and Casing Running Enigma
Abstract: TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractRunning casing in high angle and extended-reach wells is often recognized as one of the most demanding of all well construction operations. In such wells, frictional drag and unexpected downhole mechanical resistance can exceed available surface slack-off weight. The ability to reliably predict casing running performance will significantly help to reduce costs in challenging wells. Interestingly, a complex and often subtle relationship exists between a drille… Show more
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Cited by 5 publications
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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. 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.
The "Spanish Bay" well was drilled from a production platform located offshore California in 1,075 ft of water. This record setting extended reach well overcame numerous technical and operational challenges and reached a total depth of 33,435-ft measured depth (MD) / 7,663-ft true vertical depth (TVD) with 29,720-ft displacement. This paper will highlight the rig package limitations and upgrades, describe key technical and operational challenges, discuss how the challenges were addressed, and describe key / unique operations. A case history is presented describing the technical and operational challenges successfully overcome including limited hydraulics, high torque, pipe racking constraints, mud handling capacity, offshore logistics, and platform space limitations. As predicted by detailed torque and drag modeling, the well's 86º tangent angle required that drillpipe and casing be rotated into the hole to overcome the effects of negative weight. The 22,131-ft 9" × 10¾-in. intermediate liner was successfully floated and rotated to 29,831ft MD / 5,525 ft TVD. The well established a new North American extended reach drilling (ERD) record and a new global ERD record from an offshore location. Introduction Extended reach drilling refers to the practice of directionally drilling to geologic objectives located a significant distance horizontally from the drilling rig. The design and successful drilling of ERD wells require significant detailed analysis and thorough understanding of rig operating capabilities. Operators often design and build custom rigs or perform significant upgrades to existing rigs to meet the specific technical requirements for their ERD applications (McDermott 2005). Some selected upgrades were required to drill the "Spanish Bay" well, but mostly existing equipment was used. Offshore logistics and space limitations on the producing platform were also factors in the effort to achieve the objectives of this ERD well. The techniques utilized to drill this well can be used on future wells, thereby extending the reach of existing drilling packages, minimizing capital investments, producing from previously out of reach areas, and improving overall project economics. Field and Area Overview The Santa Ynez Unit (SYU) is located approximately 20 miles west of Santa Barbara, California. Operations in the SYU area comprise an oil and gas processing plant in Las Flores Canyon and three offshore platforms located in federal waters in the Santa Barbara Channel. The three production platforms (Hondo, Harmony, and Heritage) range from five to nine miles offshore, and lie in water depths of 842, 1,200, and 1,075 ft, respectively. Each platform has a company-owned drilling package installed. The oil and gas produced offshore is transported via subsea pipelines to the company's processing plant in Las Flores Canyon. These fields produce low-gravity 12 to 20º API sour crude primarily from the highly-fractured chert reservoir in the Monterey formation.
The operator and co-venturers are developing several Angola Block 15 fields in water depths of up to 1400m. To date, 83 development wells and 33 exploration / appraisal wells have been drilled in the Block. Most have experienced hole quality issues in the riserless interval that manifests themselves as tight hole while tripping the BHA and abnormal/excessive drag running casing. In a few cases, casing could not be run to total depth (TD) and in one unfortunate case, the casing buckled in open water.There has been uncertainty as to the root cause of the hole quality issues which have been attributable to various factors since drilling was initiated. A review of available literature revealed very little published information on riserless drilling and casing running practices. The operator undertook a study of its riserless drilling and casing running practices in order to look for trends that may suggest certain sources as the root cause and to allow a re-examination of long-accepted practices. The study, combined with some new perspectives on directional drilling mechanics, has identified potential root causes not previously considered. Changes to drilling practices have resulted in improved riserless hole quality and smoother casing running operations.
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