Design Of Facility Systems For Tantalum Field Engineering Essay

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This Engineering report deals with facilities development in Tantalum Oil field for Alpha Oil Company and recommends the best option for carrying out the project. Various options were considered for developing the Tantalum field and only two options were discussed in this report. First option is standalone development, where Oil production and storage is done through concrete gravity platforms and transportation is carried out by using shuttle tankers. Second option is, using the existing processing facilities in nearby Palladium platform, which is about 20kms from Tantalum oil field. The technical and commercial aspects of the two options were analyzed and best option for developing Tantalum field was concluded.

Introduction

Newly discovered Tantalum offshore field is located at about 50kms from nearest landfall and 300kms from significant town, where processing and tanker berthing facilities are present. The nearest development is the Palladium platform located at about 20kms from Tantalum. Two appraisal wells have been completed and more wells are proposed based on reservoir compartmentalization to achieve the production rate. As subsurface plans are fixed to get reservoir products, the facilities have been designed from well head to export point. Two different options are proposed in this report.

Option 1: Standalone Development

Concrete Gravity platform is used in Production and Storage from Tantalum filed. Transportation is done through shuttle tankers to the processing facility in main town situated at about 300kms.

Option 2: Using existing facilities

Transporting raw crude to the Palladium platform and process it through the existing facilities.

STANDALONE DEVELOPMENT OF TANTALUM FIELD

For transporting Oil and gas over long distances, it has to be processed to meet export specifications. The Reid vapour pressure should have to be in between 1 to 12psia and BS&W (Basic Sediment and Water) content should be less than 1%. For processing the raw crude from Tantalum field, appropriate offshore structure is required. Optimum selection of structures is vital as it involves huge capital investment.

Based on the Production capacity of Tantalum field, FPSO (Floating, Production, Storage and Offloading) and Gravity platform were considered because of their inbuilt storage capabilities as we can avoid the need for temporary storage tankers.

Steel reinforced concrete gravity platform is selected for Tantalum field based on the cost, storage capability and ease of construction. The platform can be towed to the site by emptying the caissons which are flooded at site during commissioning. The gravity force due to enormous weight of structure keeps it positioned. The decommissioning done by simply removing the water in caissons and can be towed new site.

Tantalum Facilities â€" Main process flow diagram for proposed standalone development

Crude from wellheads are gathered in subsea manifold and brought to platform through risers to the Christmas tree. The choke in production header distributes hydrocarbons into separators based on inlet pressure and test requirements. In the 1st stage High pressure separators, removed water is sent to water treatment facility. Oil is send to the medium pressure separator for further processing. The gas from high and medium pressure separators are passed through a gas Knockout Drum (KO Drum) for removing liquid condensates in the fuel gas. The high quality gas is used in Gas turbine generators for power generation and for running gas compressors. Low quality fuel gas from low pressure separators and excess gas are compressed by using two stage high pressure compressors and then injected into gas disposal well through risers.

Subsea Manifold

Hydrocarbons from the wells are gathered from the subsea tree into the manifold and transfer it to the production facility. Subsea tree is placed on every completed well, where pressure control valves and injection ports are present. No booster pumps are employed as reservoir pressure is sufficient enough to propel the crude into production facility.

Riser system:

Risers are conductor pipes between well heads at sea bed and floaters on surface. Top tensioned riser and catenary riser were considered and Metallic catenary riser was selected, based on its ability to survive from environmental loads and ability to tie-in with subsea pipelines to a fixed platform.

Figure showing the Components present in Riser Design

Separators

Three phase separator is installed in the Gravity platform for effectively separating the reservoir fluids into Oil, Water and Gas. Horizontal and Vertical separators are the two commonly used equipments to carry out the separation process. Horizontal separators are more efficient than vertical separators, if the dominant phase is oil in reservoir products.

Based on the production capacity of Tantalum field, Two 50% trains, with each train composed of three Horizontal separators are selected. A test separator is also installed parallel to the separator for well testing and analysis of flow measurement. Vortex breaker, demister and slug catcher are provided in the separators for increasing the efficiency of Gravity separation process. Parallel plate type heat exchangers are used between the separators to encourage the emulsion breakup.

Typical Three Phase Horizontal Separator

Oil treatment

As flow rates are high in tantalum platform, horizontal electrostatic treater is used to achieve the shuttle tanker storage specifications. The oil water emulsion is broken by applying electrostatic fields in the oil, which promotes the deposition of water.

Compressors

Compressors are used to increase the working pressure of gas, based on the principle of positive displacement method. Different types of compressors such as Axial, Reciprocating, Screw and Centrifugal compressors are available. The horse power rating with respect to that space and weight is high for centrifugal compressors, which makes it favorite selection for offshore applications.

Diagram showing the equipments present before Gas compression

Before entering into the compressor, the gas has to pass through the Heat exchangers. Gas compression is high at low temperature of gas. Tube and shell type heat exchangers are suggested for Tantalum platform. The liquid particles present in the gas are absorbed by using Tri Ethylene Glycol (TEG) in scrubbers, before the gas enter into compressor.

Two high pressure compressors has to be installed in the platform for compressing the excess produced gas, that are going to be disposed off in a gas disposal well through gas injection manifold.

Two low pressure centrifugal compressors are used to compress the produced gas from medium and low pressure separators.

Pumping System

Water Treatment Facility

The amount of water produced in the reservoir will be based on water cut from reservoir products. Even after separation process, sand particles will be present in water/oil emulsion in produced water. As there is good aquifer support available in tantalum reservoir, water injection facilities are not installed. Before discharging the produced water into sea, it has to be treated to meet the environmental regulations. Disposal quality of 40ppm of oil in water has to be achieved in water treatment facility. A combination of Sand cyclone and Hydro cyclone separation is installed in series to achieve the discharge quality.

Water Treatment facility selected for Tantalum field

Metering system

The transfer of ownership from producer to customer often takes place at shipping point to a shuttle tanker or pipeline operator. The payments, taxes and invoices are calculated at this point, hence precise metering system is essential.

Turbine, Coriolis, Ultrasonic and Positive displacement meters are commercially available. Based on the accuracy and wide range of fluid handling capacity Turbine meters are selected for Tantalum field.

For accurate measurement four turbine meters run along with fluid analyzers. The Volume, Density, Pressure, Temperature and BS&W are measured continuously by the analyzers. All the interfaces with the equipments are monitored and controlled by using computers. A prover loop is also installed to calibrate the meters. Multiphase flow measurement calculations based on the fluid properties were derived by API and ISO. Based on the calculations the computers were assisted to derive the amount of crude transported.

Storage and Transportation

As gravity platform is selected for tantalum field, oil is stored in concrete storage cells. Oil is pumped to the metering station and exported to the shuttle tanker through Single point Mooring system.

Picture showing Gravity platform exporting oil to Tanker through SPM

The option of transporting the oil through pipelines is not considered because of enormous cost and technical difficulties involved in laying subsea pipelines for more than 300kms. Laying 50kms subsea pipeline to the nearest landfall and transporting it through both pipeline and land tankers were also considered, but shuttle transportation is far cheaper than all other transportation options.

Power Generation

The power required for production systems, utilities and drilling operations are generated by Gas turbine generators, which makes use of maximum amount of gas from reservoir. Dry fuel gas normally operates the generators, but diesel can also be used as backup fuel.

Flare system

The flare system is installed in the platform mainly to tackle abnormal operational environment created by various equipments in the platform. The flare system in Tantalum field is not intended to burn off excess produced gas.

DEVELOPMENT OF TANTALUM FIELD USING EXISTING FACILITIES

The produced oil and gas are transported to the palladium platform located at about 20kms from tantalum field. The space available for installing new separators and related facilities in Palladium platform is not possible due to very limited space availability. The emerging subsea processing facilities are suggested for Tantalum field and further treatment are carried out using existing Palladium facilities.

Based on production forecast from appraisal wells, the expected production rates were tabulated below.

Tantalum Field production forecast

Year

Net oil (kbpd)

Water cut

Gross Production (kbpd)

Produced water (kbpd)

1

10

0.05

10.526

0.526

2

25.6

0.15

30.118

4.518

3

50.9

0.2

63.625

12.725

4

50.1

0.3

71.571

21.471

5

49.8

0.4

83.000

33.200

6

40.5

0.52

84.375

43.875

7

30.1

0.58

71.667

41.567

8

23.9

0.62

62.895

38.995

9

20

0.67

60.606

40.606

10

17.2

0.71

59.310

42.110

11

15

0.73

55.556

40.556

12

13

0.75

52.000

39.000

Palladium field current Production data

7

60

0.3

85.714

25.714

The palladium field is in its seventh year of production and have got current gross production rate of around 86kbpd. From Palladium field data, the decrease in oil production rate and increase in water cut rate has been found.

After completion of six production wells in Tantalum field, the production rate of tantalum field is expected to be around 10.6 kbpd of gross fluids. If tantalum crude is planned to process along with crude from Palladium, the production rate would be around 97kbpd. Any deviation in the production forecast of tantalum field and production rate of Palladium will decrease the production performance. To tackle this, subsea separators are used in Tantalum field and further treatment and transportation are carried out in Palladium platform.

Schematic flow chart for development of Tantalum field using existing facilities

Subsea Separation Technology

The new age subsea solutions for processing and separation of hydrocarbons on seabed itself have removed the surface production operations completely in offshore environment. With increasing oil rates, oil companies targeted the huge Arctic reserves (25% of world undiscovered oil). The promising subsea solutions have opened the doors for extracting hydrocarbons in such harsh environment.

Typical Subsea separator with Water Injection Module

Separation and Water treatment

Subsea separator is similar in design to those surface separators, but they are constructed to withstand the pressures exerted in subsea environment. Horizontal subsea separators are selected for Tantalum field. The bulk amount of water produced in hydrocarbons is removed in the subsurface separator and it is then passed on to the water treatment facility to obtain disposal quality. New generation hydro cyclone separator is employed to get less than 40ppm of oil in water to meet the environmental regulations in North Sea.

Picture showing water discharged from subsea separation system into sea

Subsea processing considerably reduces backpressure on reservoir, results in increased production rate and also increases the oil and gas recovery factor from 3 to 6% than conventional surface processing techniques.

Subsurface Multiphase flow meters and Booster pumps

The need for separator can be eliminated by installing subsea multi phase flow meter and the production can be optimized online based on the flow meter reading. The production loss during well testing period can also be eliminated by using multiphase flow meters. Virtual flow metering is used as backup solution for the downtime of subsurface flow meters.

Hybrid helicoaxial Radial pump is used to increase the pressure of fluids, which is required for transportation of oil and gas into palladium platform located at 20kms from the Tantalum field. The flow lines from booster pumps lead to Christmas tree of Palladium platform through risers.

Picture showing Multiphase flow meters and Booster pumps

The subsea separator module was not shown in the above picture. In the subsea separation process selected for Tantalum operations, the flexible flow line jumper will be connected to a production manifold in separator module. The subsea separation and pumping system is difficult to operate because of the continuous feed required by the pump from separator.

Typical Subsea separation and Piping system

The measured oil and gas reaches the palladium platform, where oil and gas are further processed using the existing facilities. The gas produced in the Tantalum can be sold to palladium owners, which can be utilized for power generation facilities in Palladium platform. The power requirements of subsea Tantalum facilities are transferred through umbilical lines. The oil blended along with the palladium oil is stored in a temporary storage barge and then transported through shuttle tankers with the help of installed single buoyancy mooring system.

“By Difference” and Oil allocation techniques are used to calculate the share of Tantalum and Palladium owners. The gross product worth of Hydrocarbons is evaluated in Oil allocation system for fair share price distribution to the owners.

Advantages of using Existing facilities

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