Schlumberger

Technical Paper: Efficient Perforation of High-Pressure Deepwater Wells

Society: OTC
Paper Number: 21758
Presentation Date: 2011
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Abstract

This paper describes the planning, logistics, and technology used in Cascade and Chinook, the two largest deepwater high-pressure perforation jobs successfully executed to date in the Gulf of Mexico (GoM). These Lower Tertiary well completions have gross perforation intervals over 800 feet and downhole pressures higher than 19,000 psi. This paper discusses the technology used in the planning stages to predict gunshock loads on completion equipment, and the logistics and procedures used to minimize costs, rig time and risks while maintaining safe operations. Perforating several intervals in one run was required to complement a single-trip multi-zone frac-pack system in which all downhole packers, screens and service tools are run at once, and all zones are stimulated in a single trip. Perforating all intervals with long gunstrings and then frac packing multiple zones in a single trip saves substantial rig time compared with performing conventional stacked frac packed completions requiring multiple trips per perforated zone.Thousands of perforating jobs are conducted successfully worldwide each month. However, there are a small number of jobs, typically high-pressure deepwater wells, where gun shock is a real and significant risk. When planning perforation jobs in deepwater high-pressure wells, engineers strive to minimize the risk of equipment damage due to perforating gunshock loads, such as bent tubing and unset packers, and a potential fishing job. For Cascade and Chinook, peak gunshock loads were evaluated with software that predicts the pressure waves in the completion fluid, and the associated structural loads on all well components. Fast gauge pressure data shows that predicted wellbore pressure transients are sufficiently accurate both in magnitude and time when the input reservoir response data is close to the actual field data.We discuss in detail the logistics and procedures used for loading and transportation of guns, building the BHA, and running the gun string in the well. The logistics for mobilizing over 700 lbs of explosives requires extensive planning to minimize time and costs. Minimizing the time needed for each gun connection is crucial to minimize rig time, and several approaches were employed.The logistics and procedures outlined in this paper led to a rig time reduction of over 67% for the execution of the largest deepwater high-pressure perforation jobs done to date in the Gulf of Mexico.

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