Strengths and Weaknesses Guide Choice of Brazilian Subsea-Development Options
Authors: Carpenter Chris 
Published: October 2018

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 28051, “Subsea Concept Alternatives for Brazilian Presalt Fields,” by Kevin Buckley and Ricardo Uehara, Shell, prepared for the 2017 Offshore Technology Conference Brasil, Rio de Janeiro, 24–26 October. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission.

This paper identifies and compares four subsea-development concepts for typical Brazilian presalt deepwater applications on the basis of generic system functional requirements; the strength, weakness, opportunity, and threat analysis method (SWOT); and comparative cost/benefit analysis. The paper provides a fast-track approach to perform screening assessment of multiple subsea concepts.

Introduction

Subsea development concepts for presalt regions such as those offshore Brazil have followed a replication methodology primarily based on a satellite configuration with flexible risers and flowlines. While this concept has several strengths, the associated scope of the operation incurs considerable cost. This concept, in addition to three others, is outlined in this paper. The concepts discussed include the following:

Satellite configuration with flexible risers and flowlines

Daisy-chain configuration with rigid risers and flowlines

Cluster configuration with manifolds, rigid risers, flowlines, and flexible jumpers

Hybrid solutions with rigid risers and flexible flowlines (with and without manifolds)

The objective of this paper is not to select the best option; rather, it is to discuss these options on the basis of application, objectives, premises, and field characteristics. Common characteristics of the Brazilian presalt fields are provided in the complete paper, and its Fig. 13 summarizes the SWOT analysis for all four concepts.

Satellite Configuration

In this configuration, each well is connected directly to the host by two dedicated flowlines/risers: The production well has one production and one service flowline/riser, while the injection well has one gas-injection and one water-injection flowline/riser. Each well has an umbilical connected directly to the host. Thus, each tree has three connection modules located on the tubinghead spool (THS), one for each flowline and one for the umbilical. A pigging loop inside the THS allows for fluid displacement, double-sided depressurization, and round-trip pigging of the flowlines. The subsea-controls system is multiplexed, with a subsea-control module on each tree.

Strengths.

Flexibility to position the wellhead on the seabed

Independent well control from topsides

Standardization of subsea systems

Installation of flexible flowlines and risers can be faster and cheaper than the installation of rigid pipes

Weaknesses.

High number of flowlines and risers (two per well)

Use of flexible lines is at the edge of technology for these materials for presalt conditions, so qualification is required

Limited inner diameter (ID)

Opportunities.

Reduce the number of risers

Use free-hang catenary risers instead of lazy-wave risers

Incorporate subsurface data to define well location in the reservoir as late as possible

Threats.

Because the subsea system is not modular, interventions tend to increase operating costs

A lack of multiple vendors capable of delivering the necessary scope of the operation