In September 2010 a decision was made to expand the current Mars field development with a second 24 slot TLP structure in a water depth of 3000 ft. This new development includes higher pressured deeper pays below the existing brown field Mars pays. The new structure will install wells with multiple casing strings across stacked sand packages that are both depleted and virgin pressured ranging from 10,500 ft to 23,000 ft TVD in depth. This in combination with other challenges such as extremely tight annuli clearances, depletion zones greater than 5000 psi, multiple stacked sands at varying degrees of depletion, and risk of borehole stability failure/ballooning presents a unique set of zonal isolation challenges that requires proactive novel approaches and design strategies. Zonal isolation is a regulatory requirement and a key component of project success in order to secure maximum field recovery and future wellbore utilization within the estimated field life.Zonal isolation methodology and design does not have a single focus but explores all parameters that affect placement and isolation while not losing focus on striving operational simplicity. This paper discusses the engineering approach to zonal isolation requirements in a highly challenging environment utilizing a step wise methodology with increasing complexity and also elaborates on how this approach led to the identification and ultimately the development of new technologies.Design methodologies will be discussed as well as resulting technologies identified as a "must haves" for development to ensure maximum probability of zonal isolation success. Technologies discussed will include reverse cementing tools, 50 (ϩ) year seals for stage collars, and connection requirements. Statement of Requirements (SORs), basic tool descriptions, and preliminary results of these developments will also be included. Discussions on why certain placement techniques or approaches were not integrated into the zonal isolation project plan will also be discussed. OverviewNumerous design challenges must be managed to ensure wellbore objectives, lifecycle wellbore integrity, robust future utility and top quartile execution performance is achieved for Mars B Olympus direct vertical access (DVA) wells. New regulatory requirements and design conditions have led to the required use of
The deepwater Mars/ Deimos field is located in the central region of the Gulf of Mexico (GoM) at~3000' water depth. Mars was discovered in 1989 and production began in 1996 from Mars A, a 24 slot tension leg platform (TLP). The deeper Deimos, with significant hydrocarbon volumes, was later discovered below the original Mars production intervals. After years of development, the shallow target horizons have been severely depleted, whereas new discovery is still at significantly higher virgin pressures.Mars B Olympus DVA, a new 24 slot TLP, was justified following a holistic evaluation of the deeper discovery. This TLP represents the first brownfield development of a deepwater field in the GoM. The field life is~50 years, with a development plan requiring ϩ/Ϫ 80 independent completions across~60 hydrocarbon horizons, extending from 10,500= to 23,000= true vertical depth (TVD). Due to the limited number of slots and required number of completions, each of the boreholes has to consider future utility (i.e., slot recoveries, slim-hole sidetracks, big-hole sidetracks and up-hole recompletions) as a fundamental design requirement.The detailed well development concept design was kicked off in 2011, considering new design load scenarios due to more stringent regulatory and internal design mandates put in place. Previously used concept design was neither robust nor satisfy long term life requirements.A representative "Type Well" design concept approach was developed to holistically evaluate existing technologies and equipment feasibility against the new design mandates and to identify gaps. The type wells were analyzed in detail to ensure there were no design oversights and so design limit envelopes could be established. Subsequently,~20 new technology developments ranging from a high-pressure NACE tieback system to a reverse cementing tool were identified as critical to project delivery, and a multitude of unintended consequences resulting from the new well design were also identified in the process.The following paper describes the methodology used to create these type wells and examples of technology gaps identified. It also describes the key technologies developed and the domino effect as a result of their implementation.
New regulatory requirements and design conditions introduced in recent years have led to the use of higher strength tubulars in the majority of Deepwater wells in the Gulf of Mexico. To achieve the new design requirements, the use of non-conventional casing sizes, grades and weights different than those traditionally used and available in the industry are required. The use of thicker wall tubular has consequently resulted in geometrical constraints and tighter annuli clearances in the wellbore driving new connection design requirements and selection criteria to meet overall well objectives. The new design conditions require innovative connection design to meet or exceed the collapse strength of pipe body rating. As part of the Shell Mars B project, the Olympus TLP DVA team championed the development and qualification of multiple connection types to meet the project requirement and for overall portfolio usage. As the number of connections to be designed and qualified is substantial, a pragmatic and systematic testing philosophy and strategy was developed for the Mars-B project TLP DVA wells. This paper provides a high level overview of the connection selection challenges, the systematic process adopted to streamline connection development, testing and qualification. It will also discuss some of the challenges in connection design to meet well requirements and qualification process. The scope includes static connection design for strings installed below the subsea well head, as well as, dynamic connection design on strings that are installed in the water column. Both connection designs require sealability qualification and assurance. Dynamic connections require additional fatigue design and qualification. Rigorousness of sealability and fatigue testing is appropriate to the environment of which it will be subjected throughout the well and the 50 year field life.
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