New Flow Assurance Solutions to Work Out Hydrate and Paraffin Blockage Problems in Deepwaters

Abstract

Hydrate and paraffin blockages are the major causes of oil production losses in deepwater scenarios like the ones existing in Campos Basin area. This paper is aimed at describing two new applications of a thermochemical method (SGN method) which has been extensively used by Petrobras (in 200+ jobs) to unplug subsea flowlines by organic deposits, viz,- to dissociate a gas hydrate buildup in a subsea christmas-tree, - and to melt a massive wax deposit accumulated in a subsea flowline ahead of a stuck pig. Both successful jobs were performed in Campos Basin, offshore Rio de Janeiro. Hydrate formed in the pistons chamber of the christmastree- cap's locking-pins was the cause of the operational failure to re-entry a subsea well (The well's christmas-tree is at 601 m water depth). This paper describes in details the designed "tailor-made" solutions to work out the problem. It encompassed the following points: development of environmental-friendly SGN formulation, - heat-exchange simulations, mechanical modifications of the regular tree-cap releasing tool, job planning and safety procedures. Along a routine pigging job, excessive wax was allowed to accumulate ahead (downstream) of a foam pig in the flowline of a well. This well produces to an FPSO. So, the pig got stuck. Our attempts to release it by means of standard procedures were fruitless. Therefore, an innovative engineering solution had to be developed. A sonic method was used to pinpoint the wax blockage. It also entailed spotting the thermochemical SGN fluid - with the aid of a coiled tubing unit - to melt the wax blockage ahead of the pig. There were some drawbacks we had to face to perform this job. For instance, there is no room enough in the FPSO turret area to place a regular coiled tubing(CT) unit out there. So, mechanical modifications had to be carried out to attach the CT's injection head to the FPSO's turret and to safely operate the CT unit from outside the revolving turret area. The paper also describes the kind of approach engineered to release the pig on a step-by-step basis. To our best understanding both approaches used to work out the two described problems are sound technology innovations. They surely are unique flow assurance solutions for deepwater scenarios. Introduction Over the last quarter century Petrobras has concentrated most of its E&P activities in the prolific Campos Basin area, offshore Rio de Janeiro State (Figure 1). Nowadays, around 82 % of all Brazilian domestic crude output come from this province. Out of this total, production facilities located at deep (1,000+ ft water depth, 300 m) and ultra-deepwaters (4,921+ ft water depth, 1,500 m) contribute with circa 84 % of the total Basin production. It is well known that deepwater production environments bring with it additional challenges to assure maximum productivity of the wells. Figure 1 - Campos Basin location, offshore Rio de Janeiro state, Brazil.(AVAILABLE IN FULL PAPER)

A Perspective View of Flow Assurance in Deepwater Fields in Brazil

“…A hydrate plug located below a tree-cap of a deep water subsea well was removed by external heating performed by a tailor-made SGN formulation (8) . The selection of the most appropriate technique will depend on the specificity of the blockage.…”

Controlling Nitrogen Oxide (NOx) Emissions from Exothermic Nitrogen Generation Systems for Application in Subsea Environments

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