Marlim 3 Phase Subsea Separation System - Challenges and Innovative Solutions for Flow Assurance and Hydrate Prevention Strategy

Abstract

This paper presents hydrate design premises established to reach the finaldesign and operational philosophy for the 3 phase subsea separation system, also known as Marlim SSAO. The main purpose of this pilot station is toseparate the produced water and reinject it into reservoir for pressure supportwhile routing the oil and gas to topside. Since the subsea process station handles multiphase flow where gas and freewater are present, and the system is exposed to low temperatures by the ambientcold sea water, a good strategy to avoid hydrate formation is necessary. Thehydrate strategy must be incorporated as a part of the total system design andshall handle all critical operational scenarios as shut-down and start-ups. Thehydrate strategy is closely linked to the temperature control and theevaluation of need for thermal insulation of the system. Temperature control isalso important in the system because of high sensitivity in fluid properties. General thermal insulation verification analysis and detailed studies of coldspots are required. Real fluid testing was included in order to better evaluatethe hydrate potential. The Marlim SSAO, as an integrated part of a field system from subsea wells totopside, is divided into several parts for the facilitation of the flowassurance and the hydrate prevention strategy: Multiphase lines, water linesand water injection system. The hydrate prevention is very challenging becauseof several open connections between the multiphase lines and the water lines. Hence, usual means as MEG inhibition and thermal insulation have not beenenough to ensure the hydrate prevention strategy and new strategies have beendeveloped. It has been necessary to challenge the strategies in every part ofthe system. The results of the work methodology and the analysis executed indicated thatMarlim SSAO is a safe system to operate from a flow assurance and hydrateprevention point of view. The material presented in here intends to establish akey reference for preservation design of 3 phase subsea separation systems. Itapplies for future generations of these kinds of equipments. Introduction The Marlim SSAO is a subsea processing pilot station which has been installedin the Campos Basin off the coast of Brazil. The objective is to separate mostof the water from the production stream and re-inject it into the reservoir forpressure support while transporting the oil and gas to topside. The SSAO isinstalled at a water depth of 876 m, 341 m from the production wellhead and2100 m from the injection wellhead. The hydrocarbons will be sent to thetopside facilities 2400 m (riser and flowline length) from the SSAO. This paper describes the challenges and innovative solutions on flow assuranceand hydrate prevention strategy for the Marlim SSAO. This includes the mainphilosophy, the preservation of the station in different operational modes, evaluations of identified risks, and calculations and analysis performed tosupport the strategy.