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CVEN: 686 TECHNICAL PROJECT- SPRING2015

Paper 1: SUMMARY ON FIELD DEVELOPEMNT PLANNING ANS FLOATING

PLATFORM OCNEPT SELECTION FOR GLOBAL DEEPWATER DEVELOPMENTS

May, 4th 2015

The authors of the paper titled FIELD DEVELOPEMNT PLANNING ANS FLOATING PLATFORM CONEPT SELECTION FOR GLOBAL DEEPWATER DEVELOPMENTS are Ricahrd Dsouza, Shiladityaa and Granherne. The authors talk about the deep-water field development and its concerned factors where deep emphasis is to be placed to reduce the economic outbursts. Importance is placed on key factors such as reservoir data, geometric conditions, fluid characteristics and surface parameters.

Deep Field Development Selection Drivers:

To achieve commercial success, critical variables are to be considered before the selection of a field. The parameters to be considered are listed below:

a. Reservoir geology & Geometry: Permeability and porosity are main factors for a

RESERVOIR ROCK and for the well performance. Higher are these parameters, higher is the performance.

b. Reservoir fluid properties: These properties are a key factor for performance of wells. Thus they have a great financial impact on the project. These properties are used by the engineers to assure wells and hydraulic models.

c. Drilling and Completions: As always, drilling is laborious, time consuming and a costly activity. This could even consume 50% of the project cost. Well performance is linked to the effectiveness of completions which at times could equal to the cost of drilling.

d. Regional considerations: There are several sub considerations which are listed below: Block size: The area to be leased to a party and deployment of exclusive resources

for the same. Infrastructure and Markets: Availability of pipelines and other infrastructure needs

required to transport the drilled oil/ other minerals. Local Content: the client requirements such as establishment of facilities,

fabrication yard, etc. Terms and conditions / regulations: Various factor can be jotted in here, such as

delay in approvals, land acquisitions, contractual violations etc. e. Site Characteristics:

Water Depth: The water depth at the location of structure is an important factor. The varies the design of mooring systems, risers, pipelines and various required structures, obviously its an impact to the project.

Ocean conditions: The extreme wave conditions will change the structural aspects of the structure. There by increasing the cost.

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Floating Process Selection Process:

The utility, size, location, geometry and complexity of the subsurface drilling will lead to a

selection of floating platform. The typical selection process is mentioned below:

Functional requirements established: A decision on the floating process can be made after knowing the requirements of the structure to be built.

Technical constraints accessibility: Knowledge on the technical constraints of the location and of the structure is of prime importance for longevity and construction ease of the structure.

Risk of life cycle vs economics comparison: This parameter is an importance to the client. A comparison of investment vs. capex, equipment and maintenance is to be prepared before even planning the structure.

Operators strategies and etc.: Health safety environment (HSE), sustainability, design/ method standardization and contract facilities are also an impact to the cost of the project which are to be taken care of.

Field Development Drivers and Floating Platform Selection In Deepwater: The US GOM has prepared an extensive oil and gas pipeline grid over the decades.

Developments in the regions of Green canyon and Mississippi are accounted towards the deep-water developments. Two major geological trends for deep water discoveries are of the Miocene and Lower tertiary periods.

Developments in the Miocene Trend: High permeable soil ensure high well rates. Huge platforms in remote areas have made an impact to ensure the infrastructure. The reservoirs risk mitigation plan was adopted to ensure the faulted reservoirs. Three platforms were located at 5000 ft below water to produce multiple drill centers. Due to high cost and technical challenges, TLP were eliminated.

Developments in the Lower Tertiary Trend: Several discoveries in this regard were made in 2002. The development plan is to produce 2 clusters which holds back the deep draft protection. The development of the field and depth of water will narrow the choice to choose a host platform.

Conclusions: Deep-water generates about one-tenth of the global oil supply. The industry has begun

doing explorations and looking for deep-water reserves. The authors present an insight for the

required parameters to be dwelled into before making a choice of investing millions of dollars. All

the discussion in paper boils down to sticking to the business strategies, reservoir performance,

maximizing the return of investment and multi-disciplinary interaction plan.

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Paper 2: SUMMARY ON FIELD DEVELOPEMNT PLANNING ANS FLOATING

PLATFORM OCNEPT SELECTION FOR GLOBAL DEEPWATER DEVELOPMENTS

The author of the paper titled PREDICTION OF THE DAMPING-CONTROLLED RESPONSE OF OFFSHORE STRCUTRES TO RANDOM WAVE EXCITATION is J. Kim Vandiver. The author presents a method to find the structures damping controlled response using natural frequency to random wave forces. Examples of the response estimate of fatigue analysis of tension leg platform is considered.

Principle of reciprocity is used to eliminate the force calculations. The wave force spectrum is dependent on the amplitude and the radiation damping. Although the damping ratio of the radiation is difficult to determine it is useful when the dynamically amplified response is necessary. The techniques in the paper are pretty new to the field, however they have a larger reach and wide applications.

Key Points:

Contrary to the general belief that total damping is inversely proportional to the response, but is actually proportional to the ratio of radiation damping to total damping.

Linear wave theory is assumed (Drag force is not considered) The direct spreading of wave spectrum is important on calculating dynamic response. Absolute term wave force evaluation is not required. The extreme events are modelled stochastically on the prescribed design waves.

Linear Oscillator Model:

Though there are humongous volume of frequencies, only certain frequencies are important to wave forces which are subjected to dynamic response. The ratio of wave force amplitude to structural member diameter is in the order of one or less for linearity of wave force.

When the vibration is linear and small, the response can be recorded by the modal analysis of SDOF (Single degree of freedom). Super positioning can be used for the response of individual SDOF system. In the equation of motion, the hydrodynamic forces can be represented as a function of acceleration, velocity and displacement in the wave particles & coordinate motion of the structure and its stiffness. For the motion of waves on a rigid structure, the dynamic loads are just added to the loads of the structures.

High cycle low-stress fatigue considerations where forces are linear is one application. This modal cannot be applied to relatively small structures, subjected to heavy/ large

waves. Near the natural frequencies, the total mass and damping coefficient can be considered to

be constant within in a narrow band of frequency.

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Reciprocity Relations:

Due to presence of hydrodynamic pressure and pressure field, it becomes complicated to evaluate for hydrodynamic forces. So, the force depended on the velocity potential is considered. The modal radiation damping is in relation to the modal exciting force.

The Haskind /Newman relation shows that the radiation damping is proportional to the square of the exciting force integrated over all angles of incidence.

A shape function, which is a constant is established to measure the directional spreading. The wave force spectrum is expressed in terms of amplitude spectrum and the radiation

damping.

Response of a SDOF resonator to Random Excitation:

As the name suggests, the total vibration is categorized as single degree of freedom system for vibration mode.

Dynamic parameters such as damping ratio, radiation damping and wave force spectrum are dependent on the frequency.

Half power bandwidth is to be used for an accurate response. Increase in damping, increases the error in calculations.

Elimination of explicit wave forces calculation:

The wave force spectrum in terms of the radiation damping are substituted by the mean square response of the half power bandwidth method without need for force calculation.

The damping controlled response dependence on the ratio of radiation to total damping is established which has an upper bound limit of one when excitation is provided by linear waves.

Damping induced coupling:

This phenomenon makes it possible to transfer the vibration energy between the nodes. When evaluating response predicted analysis, coupling is not significant. Due to small asymmetries in the structures, coupling arises which is negligible and can be

ignored.

Conclusion:

In the paper, a method was presented to evaluate for damping controlled dynamic response of offshore structures. Various serious assumptions have been made. Take away from this paper is mentioned below:

Linear wave force spectrum can be expressed in terms of radiation damping. A method to estimate damping controlled response of structural node was presented. An outlook on role of damping in evaluating for dynamic response was presented.