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Hole enlargement while drilling (HEWD) is an important technique in both deepwater and onshore drilling. Drilling interbedded formations is a difficult HEWD application. Two extreme cases can occur. One case is when the reamer drills in soft formation while the bit is in a harder formation. The other more difficult situation is when the reamer is in a hard formation while the bit drills ahead in soft formation. The latter creates an enormous challenge for the reamer to drill the harder formation without inducing large lateral and torsional vibrations which is detrimental to the reamer and other BHA components. An overall HEWD operating parameter management approach can greatly reduce probabilities of tool damage and unnecessary tripping while dramatically reducing drilling costs. A state-of-the-art BHA dynamic analysis program that allows modeling the reamer and bit in different formations plays a vital role in the overall HEWD management process. Before any planned HEWD operation, various possible operating scenarios can be virtually simulated through the BHA dynamic analysis program to evaluate the effect on BHA components of lateral and torsional vibrations. An optimized BHA configuration can be specified through these analyses and a set of optimal operating parameters for the chosen BHA can be developed. This paper presents an excellent case study of HEWD through severely depleted interbedded formations in the Gulf of Mexico. Previous offset wells had required multiple runs to HEWD this section due to reamer cutting structure damage. Models were constructed to compare performance with a range of BHA, WOB/WOR and RPM combinations. A set of optimal operating parameters and a road map were established for managing these parameters on the rig. Most importantly, the analyses recommended operating conditions that were substantially different from the accepted HEWD operation of increasing weight on bit (WOB) in harder formations. The analyses indicate that overall BHA performance was dramatically affected by weight on reamer (WOR). With a small sacrifice of ROP in the harder, more abrasive formations the HEWD system can effectively drill through the entire section without tripping due to component failure. This approach achieved excellent overall cost effective performance saving the operator $1.89 million on an offset well. Introduction The operator announced its field discovery in the Gulf of Mexico's Mars Basin in September, 2002. It is in 3,000ft of water, and is located approximately 88 miles southeast of Port Fourchon, Louisiana (Figure 1). During recent field development, the operator experienced problems with a BHA component. Specifically, the reamer 1,2 was suffering cutting structure damage driving up field development costs and slowing time to production. This paper will present the application challenges and resulting tool issues in addition to the problem analysis and engineering design changes to the reamer and operating parameters intended to solve the problem(s). Finally, the authors will present the results of applying the new technologies and operating parameters on the WELL #3 and how they saved the operator $1.89 million compared to costs incurred drilling the offset WELL #2.
Hole enlargement while drilling (HEWD) is an important technique in both deepwater and onshore drilling. Drilling interbedded formations is a difficult HEWD application. Two extreme cases can occur. One case is when the reamer drills in soft formation while the bit is in a harder formation. The other more difficult situation is when the reamer is in a hard formation while the bit drills ahead in soft formation. The latter creates an enormous challenge for the reamer to drill the harder formation without inducing large lateral and torsional vibrations which is detrimental to the reamer and other BHA components. An overall HEWD operating parameter management approach can greatly reduce probabilities of tool damage and unnecessary tripping while dramatically reducing drilling costs. A state-of-the-art BHA dynamic analysis program that allows modeling the reamer and bit in different formations plays a vital role in the overall HEWD management process. Before any planned HEWD operation, various possible operating scenarios can be virtually simulated through the BHA dynamic analysis program to evaluate the effect on BHA components of lateral and torsional vibrations. An optimized BHA configuration can be specified through these analyses and a set of optimal operating parameters for the chosen BHA can be developed. This paper presents an excellent case study of HEWD through severely depleted interbedded formations in the Gulf of Mexico. Previous offset wells had required multiple runs to HEWD this section due to reamer cutting structure damage. Models were constructed to compare performance with a range of BHA, WOB/WOR and RPM combinations. A set of optimal operating parameters and a road map were established for managing these parameters on the rig. Most importantly, the analyses recommended operating conditions that were substantially different from the accepted HEWD operation of increasing weight on bit (WOB) in harder formations. The analyses indicate that overall BHA performance was dramatically affected by weight on reamer (WOR). With a small sacrifice of ROP in the harder, more abrasive formations the HEWD system can effectively drill through the entire section without tripping due to component failure. This approach achieved excellent overall cost effective performance saving the operator $1.89 million on an offset well. Introduction The operator announced its field discovery in the Gulf of Mexico's Mars Basin in September, 2002. It is in 3,000ft of water, and is located approximately 88 miles southeast of Port Fourchon, Louisiana (Figure 1). During recent field development, the operator experienced problems with a BHA component. Specifically, the reamer 1,2 was suffering cutting structure damage driving up field development costs and slowing time to production. This paper will present the application challenges and resulting tool issues in addition to the problem analysis and engineering design changes to the reamer and operating parameters intended to solve the problem(s). Finally, the authors will present the results of applying the new technologies and operating parameters on the WELL #3 and how they saved the operator $1.89 million compared to costs incurred drilling the offset WELL #2.
The Chihuido de La Salina field is located in the folded thrust belt of the Neuquén Basin in west-central Argentina, about 200 kilometers northwest of the city Neuquén (Figure 1). The field contains several fault blocks, which produce both oil and gas. Generally, production is controlled by a thrusted anticline, structurally high in the north and relatively low to the south. The most important portion of the field produces oil from the steeply dipping flanks. Efficiently drilling the swelling clay formations of the Neuquén group (Upper Cretaceous), in Chihuido de La Salina field (ChLS), has been a distinctive challenge and is the subject of this paper's analysis and multiple-well case studies. Clay Mineralogy To better understand the clay swelling issues in Chihuido de La Salina field, a basic review is provided of the Neuquén group shale formations. The group consists of terrestrial sediments (Figure 2) laid down during the Rio Grandico sedimentary cycle (Upper Cretaceous). The formations contain two main shale constituents including smectite (70%) and illite (20%). In the smectite shales, montmorillonite is the most critical mineral with regards to swelling. If an atom of aluminum (Al3+) is replaced by an atom of magnesium (Mg2+), it will cause an additional electron or negative charge (Figure 3). The net negative charge is compensated by cation adsorption on the surfaces of the external/internal structure and is likely to cause a phenomenon know as "exchangeable clay cations." These charged cations can be either an ion of sodium (Na+) or a double charged ion of calcium (Ca2+) or magnesium (Mg2+). This reaction produces either sodium montmorillonite, calcium montmorillonite and/or magnesium montmorillonite. The change in clay mineralogy reduces the strength of the repelling forces between layers allowing water to enter and occupy the intra-layer space. Smectites have an expandable structure which increases colloidal activity due to a significant increment of specific surface. All of the structure's surfaces, including intra-layers are available to hydration and cationic exchange. These characteristics give montmorillonite the capacity to swell between layers due to hydration (Figure 4). Although illite clays have the same basic structure as montmorillonites, they don't normally display the same swelling characteristics. In Chihuido de La Salina field, the 8–1/2" hole section must be drilled through formations that contain 70% of the problematic smectite shale constituent, negatively impacting drilling economics. Background - Drilling the Neuquén Group Initial field development began in 1995 using water base mud (WBM). Despite the presence of a potassium chloride inhibitor in the mud, the operator was experiencing severe lost-time incidents related to swelling clay formations in the 8- 1/2" hole section including excessive trips to ream, wash-over, free stuck pipe and in the worst case scenario, sidetracking due to BHA lost-in-hole. To help improve field economics, the operator began utilizing oil base mud (OBM) in 2003 significantly reducing the clay swelling issues. However, it became necessary to increase the mud weight to 10–11 ppg in order to stabilize the hole and limit salt intrusion into the wellbore slightly reducing drilling efficiency. In spite of the OBM success, environmental issues forced the operator to return to WBM in 2006, resulting in the same lost-time incidents previously associated with the swelling clay formations in the Neuquén group.
The increasing necessity for hole enlargement while drilling (HEWD) technology has resulted in an essential need for engineers to fully understand the interaction between the drill bit and the hole opening tool. Inefficiency and damaging bit and bottom hole assembly (BHA) vibrations, caused by improper bit and reamer selection when drilling through interbedded formations and formation transitions, are a leading cause of inconsistent performance including excessive torque, low rate of penetration (ROP) and downhole tool failures (DTF). To mitigate vibrations, operators required a comprehensive analysis system/process that would allow them to model the complex BHA interaction in a virtual environment and quantitatively compare the performance of various design scenarios. To solve the challenge, the drilling team utilized a comprehensive, 4-D finite element model that couples laboratory results with a sophisticated computer simulator that calculates the drilling system’s dynamic performance from the bit back to surface in a real-time domain. Unlike other modeling programs that assume the contact forces between the cutter and rock, this advanced model utilizes exact cutting structure details coupled with the laboratory-derived rock mechanics to accurately predict the behavior of the bit and reamer with the entire drill string and bottom hole assembly. The effects of each specific BHA component and variations in drilling parameters on vibrations, ROP, and directional tendency can then be quantitatively evaluated.
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