An analysis of recent run data from two fields in Eastern Venezuela documents large metal seal bearing roller cone bits (16" & 17–1/2"), with a new generation steel tooth cutting structure, can be used for a much greater number of total bit revolutions than prior generation bits. The new generation metal seal has proven its ability to significantly extend bearing life and reliability and thereby provide significant reductions in drilling costs. Penetration rates have more than doubled with total footage up 89% in some instances, with less overall cutting structure wear. Cost savings of up to $121,000 US per well have been documented. The authors will describe the application of these new bits and present case studies that document significant performance improvement in the Santa Barbara and Mulata fields of Eastern Venezuela. They will also describe the development of the latest generation metal sealed bearing package and the metallurgical and design improvements of the new steel tooth cutting structures. Application Background Since 1990, over 400 wells have been drilled in the oilfields surrounding Punta de Mata in Monagas County of Eastern Venezuela. Since 1994, a turnkey operator has drilled over 55 wells, under contract with Petroleos de Venezuela S.A. (PDVSA). These wells were mainly in the Santa Barbara, Mulata and Pirital Fields (Figure 1). The hole sizes are generally 26", 17–1/2", 12–1/4" and 8–3/8". The general casing program is depicted in Figure 2. The 17–1/2" hole section is typically vertical and generally drilled from 1,000 ft to 7,000 ft, measured depth (MD). However, several 17–1/2" sections were drilled directionally when high vertical displacement was required. By the end of the operator's turnkey contract with PDVSA, a much higher number of 17–1/2" directional sections were required. The 12–1/4" interval is where the majority of the directional work takes place in these "S" type wells. The subject wells are typically drilled to the Naricual (Triassic) or KP (Jurassic) sandstones. Formation penetrated during the drilling of the 17–1/2" hole section includes Mesa-Las Piedras, La Pica and Carapita Shale formations. In some instances the Sigmolina and Textularia formations are penetrated. All of these formations are Pleistocene to Miocene in age (Figure 3). The Mesa-Las Piedras formation is comprised of soluble claystones with sandstone stringers and coal seams. Additionally, some limestone stringers and siltstones can be encountered. The La Pica formation is comprised mainly of claystones and hydrateable shales. The Sigmolina and Textularia are also shales, with high amounts of claystone and siltstone. Rate of penetration generally slows when these formations are encountered. The 17–1/2" hole section usually bottoms in the Carapita Shale where 13–3/8" casing is set. Open hole sonic logs are not run in the 17–1/2" section, thus unconfined compressive strengths are not available. Attempts to drill the entire section with a single PDC bit have resulted in inconsistent performance. This is due mainly to durability problems with light set PDC bits while drilling the hard sandstone stringers, and balling problems with heavy set PDC bits while drilling the reactive claystones.
This paper discusses the Remote Operated Vehicle (ROV) Interfaces with the Mensa Project Subsea System. The main focus centers around the design criteria, fabrication, and testing of two new ROV tools, the Seal Removal and Replacement tool (SRRT) and the Auxiliary High Pressure HPU (AHPU). The paper also provides a brief description of the operational philosophy that allows the ROV to perform multiple tasks during standard and critical path operations. Introduction The ROV is the "subsea presence" of all deepwater subsea projects. This tool provided a method of interfacing with the subsea equipment. All of the Mensa subsea equipment was designed for ROV (diverless) intervention. The Mensa satellite subsea equipment (tubing head, tree, tree cap and jumpers) was installed from the drilling rig in 5,300 ft. of water using an ROV. General ROV Configuration A 100 horsepower workclass "ROV of opportunity", rated for 8,200 ft., was used to support the Mensa Project from the drilling rig. It has two manipulators to handle the ROV tools and perform all of the intervention tasks. Fiber optics were used to support five cameras, sonar, and vehicle communications. The vehicle was launched through its own moonpool on the drill rig about 40 ft. from the center of the rotary table. Planning The need for an ROV interface register was identified early in the project. The register was used to capture all of the ROV's tasks from simple observation to complicated interventions. As each task was identified it was reviewed for ROV feasibility, tooling, and risk; it was then developed into an operational procedure. The ROV intervention register proved useful early on where it identified subsea tasks that were very difficult or impossible to perform without mission-specific or special tools. The register was beneficial offshore. It helped in vehicle task sequencing to keep the vehicle off of the critical path, ensuring that the vehicle was configured properly for each task, and providing a means for continuity throughout the project. Special Tooling Early in the project, two specific ROV interfaces were identified that could not be accomplished with existing tools. The Seal Removal and Replacement Tool (SRRT) was designed and built to remove and replace unserviceable seal assemblies without recovering the subsea equipment. The Auxiliary Hydraulic Power Unit (AHPU) was built to accommodate a multiple of incompatible fluids at higher pressures without contaminating the ROV's main HPU. SRRT The SRRT consists of a family of tools. (Table 1 - Fig. 1) They were designed and specifically built to remove and replace seals in both the Mensa manifold and trees where ROV accessibility is extremely limited. The tool set consists of three horizontal and two vertical tools designed to carry both flowline and multiport seal assemblies. The tools are intended to be deployed, powered, and operated by any standard work class ROV. Function. The SRRT consists of three major components, the tool alignment frame assembly (Fig. 2), the seal head assembly (Fig 3.), and the lock down pin. The tool is operated by functioning the three hydraulic valves on the tool's ROV panel. The up/down function lowers the seal head between the mandrel and connector.
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