Intermediate String Design Enhances Intelligent Deepwater Completions
Authors: Carpenter Chris 
Published: June 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 22087, “One Innovative Intelligent Completion Intermediate String Design for Deepwater Gas-Well Completions: The Installation Case Study From L Gas Field, China,” by Shu Jie Liu, Yi Huang, and Wen Bo Meng, CNOOC, et al. The paper has not been peer reviewed. Copyright 2022 International Petroleum Technology Conference. Reproduced by permission.

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An intelligent completion design was installed in two wells in China’s L field deepwater project. Both wells have dual-zone stack-pack sand-control lower completions. To handle critical well-control concerns and enable production from each zone, an intermediate string was installed to isolate the reservoir in each zone temporarily. While the complete paper details both the completion string design and its field installation, this synopsis concentrates on the former aspect of the project. This practice will benefit upcoming deepwater well-completion designs, especially for high-pressure/high-temperature gas-field-development projects.

Introduction
The L field is a deepwater gas field in the Qiong Dongnan Basin with a water depth from 1200 to 1500 m in the South China Sea. The field was discovered in 2014; development launched in early 2018 with a plan for 11 development wells. The target zone of this field is over 3000 m true vertical depth with a widely distributed thin layer of sand deposition. The target zone has a normal pressure gradient of 1.2 and temperature that reaches 93°C.
The 11 wells planned included six horizontal and five deviated wells. The openhole drilling of the first well began in April 2020, and the cased-hole intelligent completion of the last well was finished in March 2021. The openhole gravel packs in the first three wells were completed as the first batch. One cased-hole single-zone gravel pack was completed as the fourth well because it sat on the same flank of the reservoir as the first batch of three openhole wells. After that, a floating rig was mobilized on the other flank to complete the remaining three openhole wells. Then, the remaining two cased-hole single-zone gravel-pack completions followed. The most challenging completion, a dual-zone stack-pack intelligent completion, was performed in the last two wells in February and March 2021.
A dedicated project manager and team were assigned throughout project execution. The project-management team strictly adhered to the operator’s completion project-management system; managed the interfaces, risks, and schedules through a scientific approach; and provided technical and troubleshooting support in a timely manner.
All 11 wells were completed by April 2021, including the two intelligent well completions. The entire field was brought into production by mid-2021.

Well-Completion Design Challenges
Because of the unconsolidated sandstone present in the field, all 11 wells required a proper sand-control lower completion to eliminate the issue of sand production. However, the geologic conditions of widely distributed sand deposition and a thinly layered gas reservoir required the operator to use three different types of lower completion methods in one project: the openhole gravel-pack method for six horizontal wells to develop small and thin sand deposits, the single-zone cased-hole gravel-pack method for a sand-control completion in the three deviated wells, and the dual-zone stack-pack method for two intelligent completion wells for a dual-zone sand-control lower completion.