GOM Export Gas Pipeline, Hydrate Plug Detection and Removal

Abstract

Hydrate blockage detection, remediation and removal are successfully applied in a hydrate plug incident in the GOM. A hydrate plug occurred in mid-October 2002 in the Williams Field Services (WFS) owned and operated, 36-mile long, 10- inch gas export pipeline from ChevronTexaco's Genesis Green Canyon 205 (GC 205) platform (2,600 ft water depth) to the downstream Ship Shoal 354 platform (SS 354) platform (460 ft water depth). ChevronTexaco's Flow Assurance experts, ChevronTexaco's Genesis Asset Team, and WFS team worked together to detect, locate and remediate the hydrate plug in a safe and timely fashion while ensuring personnel safety, maintaining pipeline and riser integrity and minimizing loss of production. This paper shows how a concentrated team effort and deployment of the right tools such as transient models, hydrate formation and dissociation models, can be used to predict and alleviate a flow assurance problem, such as hydrates, which can occur in deepwater oil and gas production in a subsea system. Introduction The Genesis development1 was brought on stream in February 1, 1999. In mid-October 2002, following two major shutdowns due to strong hurricanes and one for WFS planned maintenance, gas flow into the dry gas export pipeline to SS 354 was obstructed and gas delivery to shore was halted. Analysis of the measured hydraulic data prior to and during the incident showed that the obstruction in the gas pipeline was due to the presence of hydrates corresponding to low spots in the pipeline. Operations personnel in New Orleans, working in conjunction with Flow Assurance personnel in Houston were able to locate the hydrate plug via hydraulic and hydrate models based on the measured pressure, temperature and gas flow rate during the incident. Hydrate formation caused by the presence of water and natural gas components at high pressures and low temperatures in a deep-water subsea pipeline can occur during shutdown or start-up of a pipeline as was the case with Genesis. Under normal flowing conditions, dehydrated gas flows through the uninsulated Genesis export gas pipeline. Although pressures in the line were high (~1,600 psig at inlet) and temperatures as low as 42 °F in the coldest sections of the pipeline, hydrate formation was not expected due to the low water content of gas from dehydration at GC 205. However, in the presence of sufficient water, pressures and temperatures of the flowing stream in the pipeline were conducive to hydrate formation. Since water content of gas entering the pipeline was routinely monitored below hydrate formation content while flowing, hydrates should not have formed in the pipeline during steady state flow. When hydrates did form in the pipeline, many factors may have contributed to that formation such as the multiple shutdowns within a few days of each other and the added complexity in the procedures of shutting the platform down and starting it back up. During these back to back platform shut downs and start-ups, if any water had entered into the pipeline due to non-optimal dehydrator performance, the potential for hydrate formation would have been be high. Overview Genesis is ChevronTexaco's first deepwater oil and natural gas drilling and production facility located in 2,600 ft of water in the Gulf of Mexico, 150 miles south of New Orleans. The field is operated by ChevronTexaco with 56.67% working interest, and partner ExxonMobil with 38.38% working interest and PetroFina Delaware, Incorporated, with 4.95% working interest.

Real-Time Flow Assurance Monitoring With Non-Intrusive Fiber Optic Technology

“…During normal flow, the pipeline can become uninhibited or under-inhibited reasons including the following, some of which have been discussed in the literature [2], [6] :…”

Monitoramento Da Temperatura De Óleo Em Um Sistema De Tubulação Multicamadas Utilizando Filtro Bayesiano Asir

“…equação tem os fluxos expressos pelo sinal da derivada, assim, na primeira integração, aparecem os fluxos nas fronteiras do volume elementar, o que equivale ao balanço (Maliska, 2012).…”

“…A formulação explícita dá origem a um conjunto de equações algébricas que podem ser solucionadas separadamente, sem a necessidade da resolução de um sistema linear. Já a formulação implícita resulta em um sistema de equações dependentes entre si (Maliska, 2012). A forma explícita possui restrição na escolha do tamanho do passo no tempo, já o esquema implícito resulta num sistema cuja solução demanda alto custo computacional, porém a formulação implícita representa uma interessante alternativa para solução de problemas bidimensionais parabólicos (problemas que envolvem convecção) e elípticos (envolvem difusão), por decompor a matriz pentadiagonal em matrizes tridiagonais que podem ser resolvidos pelo algoritmo de Thomas (Fletcher, 1988).…”

“…Essas estruturas podem acarretar riscos de segurança à produção multifásica em dutos, pois se depositam em sua superfície formando "plugues", que podem causar diminuição da vazão ou o bloqueio total das linhas submarinas (Kashou et al, 2004). A formação de parafinas é um fenômeno natural da maioria dos óleos devido à presença de parafinas de alto peso molecular, podendo ser acelerado devido ao decaimento da temperatura (Vianna et al, 2013).…”

Hydrate Formation Characteristics of Natural Gas During Transient Operation of a Flow Line

“…In this case, at restart, the intense agitation and mixing can promote a rapid rate of hydrate formation resulting in localized hydrate plugs which may cause complete blockage of the flow. Hydrate incidents at restart have been reported to occur whenever these conditions are found in the production [1] and export pipelines [2], manifolds [3] and well trees [4]. Comprehensive flow assurance challenges must be implemented to enable secure and stable production form gas fields especially in deep water and subzero temperature such as Ormen Lange Field, where the risk of hydrate and ice formation is ever present [5].…”