Facilities Engineer Assessment Of Three Field Development Options With A Clear Recommendation

Facilities Engineer Assessment Of Three Field Development Options With A Clear Recommendation

Introduction

The gazelle oil field is located forty five kilometers from the nearest land fall to the North West-a remote desert region with limited infrastructure. Water depth is 100m. The nearest town, Fort Thompson, 200 km south west of the field, has a deep water port with tanker berthing capability, a refinery and export facilities. The oil refining facility in the fort Thompson currently processes crude oil and NGLs from a number of onshore fields to the south and west in addition to the gazelle production. There is a strong local market for natural gas for power generation. This paper assess three field development options for the gazelle offshore oil field, which has been producing for a number of years. The development options are refurbishment to upgrade the present system, replacement of oil export system via the FSO and complete system replacement.

Question 1

Refurbishment of Present System

The present water handling and treatment system entails allowing water to settle in an FSO tank, which is discharged directly overboard, when the requirements of oil in water specifications to be met. This system has worked over the years and will still to offer an alternative when proper refurbishments are carried out. The FSO tank for the gazelle oil field needs to be changed since its nearing the end of its useful life. In changing the FSO tank a centrifuge system will be integrated to ensure the waste water produced is with acceptable limits. The centrifuge system is used with the aim of reducing the oil content in water produced in oil operations. Separation of oil and water in the centrifuge is as a result of the action of centrifugal forces as well as the specific gravity difference of water and oil (Emmanuel, 15). Produced water from the oil drilling process is inserted into the centrifuge. In the centrifuge, the water is rotated at very high speed. Water will accumulate at the exterior of the centrifuge while oil will gather at the inner layer. Water and oil are removed individually, under controlled conditions. The oil and water interface has to be sustained. Oil is usually pumped back into the process while the water is removed. A centrifuge permits the separation of minute oil droplets than the hydrocyclone even though it consumes more the energy (Samson 8). Centrifuges are normally applied as a purification step when the performance standard cannot be accomplished. In the gazelle offshore oil, the use of centrifuges will be useful in maintaining the standard of the waste water as well as removing skimming from degassers as well as induced gas flotation units, hence preventing the accumulation of sludges.

WATER

SEA BED

Figure 1: showing oil flow to ESO from the wells

Replacement of the Oil Export System via the FSO

A floating, storage and offloading (FSO) unit can be defined as a floating vessel utilized in the offshore crude oil and gas production industry for the production of hydrocarbons and for storage of oil. The FSO vessel is built to receive crude oil drilled from a close by platforms, process them, as well as store the crude until it can conveniently be offloaded onto a receiving tanker or, less often, transported via a pipeline. FSOs are used more in frontier offshore areas as they can be installed easily, and do not need a local pipeline structure to export oil. FSOs may be a modification of an oil-tanker or may be a vessel created particularly for the application. (Mollard and Robert). Crude oil drilled from an offshore platforms may be transferred to the mainland through the use of a pipeline or tanker. When the tanker is selected to transport the crude oil, it is essential to collect the oil in a storage tank so that the oil-tanker is not incessantly occupied during the crude oil production. It should only be used once significant oil has been accumulated to fill up the oil tanker. At this stage, the transport tanker links to the storage units’ stern and oil is offloaded.

FSO vessels are predominantly effective in deep-water or remote locations where the seabed pipelines aren’t cost effective. FSOs remove the requisite of laying costly long distance pipelines from the production/processing facility to the onshore terminal. This creates an economically suitable solution for minor oil fields, which could have their oil exhausted in a short period of time. Also, once a fields’ oil resources are depleted, the FSO may be transferred to a different location. Some FSO contain both processing and storage equipment for the produced crude oil or natural gas. The usual design of most FSOs contains a ship shaped vessel, having topsides and processing equipment, in the vessel’s deck as well as a hydrocarbon storage tank below within the double hull. Once crude oil has been collected and in some cases processed, the FSO stores gas or oil before offloading intermittently to shuttle tankers or transporting processed petroleum through pipelines. Fixed in place by several mooring systems, FSOs are very useful development solutions for deep-water as well as ultra-deep water fields. The central mooring system enables the vessel to move freely to adequately respond to different weather conditions, while spread mooring systems anchor the FSO from different points on the seafloor. Normally attached to subsea wells, FSOs collect hydrocarbons from the subsea production wells via a matrix of in-field pipelines. Crude oil tapped using subsea wells, are transmitted with the aid of flowliness and risers, which move the oil as well as gas from the seafloor to the turret of the vessel and then into the FSO usually floating on the surface of the water. The processing equipment on the FSO is same with what would be seen on other production platforms. Normally built in modules, FSO production equipment consist of gas treatment, water separation, oil processing, gas compression and water injection, among others. Crude oil is transferred to the double-hull of the vessel for storage. Hydrocarbons are stored onboard are later transferred into ocean barges or shuttle tankers going ashore, through a loading hose. Transporting oil from the FSO stern to the shuttle tanker bow termed tandem loading.

The FSO can be replaced using the installation of pipes. The gazelle offshore oil field can replace the FSO unit. The collected water and oil are separated after drilling from the wells. The separated oil is moved through pipelines to the refinery while the collected water is treated and re-injected into the earth’s surface.

WATER

SEA BED

Complete system replacement

Hydro-cyclones and Down Hole separation will be used together with pipes in crude oil drilling to completely replace the FSO unit. Hydro-cyclones can be described as an existing and established technique for the extraction of dispersed oil from large oil fields (Henry, 18). Oil and water separation in the hydro-cyclones is also based on the action of centrifugal forces as well as the difference between the specific gravity of water and oil (Ojo, 24). The water produced is inserted under pressure tangentially. A hydro-cyclone usually consists of two exits on its axis: the smaller exit at the bottom (reject or underflow) and a larger exit at the top (accept or overflow). The underflow is usually the coarser or denser fraction, while the accept or overflow is the finer or lighter fraction. Forward hydro-cyclones remove elements, which are denser than their surrounding fluid, while the reverse hydro-cyclones remove elements that are usually less dense than their surrounding fluid. Normally, in the reverse hydrocyclone, at the apex the overflow takes place while at the base the underflow occurs. Parallel flow hydro-cyclones also exist in which the reject and accept are ejected at the apex. Parallel flow hydro-cyclones remove elements, which are usually lighter than the fluid in the surrounding. Hydro-cyclones can be manufactured from metal (mainly steel). Metal hydro-cyclones are utilized in situations where more durability or strength in terms of pressure or heat is required. In situations where the level of abrasion is high, polyurethane functions better than ceramics or metals. Metals covered with polyurethane are utilized in cases of collective high pressure and abrasion. In a solution of particles having the equal density, a sharp cut may be made. The particle size in which the particles are separated is directly proportional to the cyclone diameter, feed pressure exit dimensions, and the comparative characteristics of the liquid and the particles. The separation efficiency is related to the concentration of solids: increased concentration will reduce the separation efficiency. An important difference in the suspension density exits between the exits at the base (fines) as well as the exit at the apex, where the liquid flow is low. When the range of the element and particle size is restricted, differences occur in the density between different particles types, the particles that are denser would exit specially at the apex. The hydro-cyclone shape creates a speed increase, resulting in creation of a large centrifugal forces as well as the separation of water and oil. The heavier water would move within the vortex in the direction of the cyclone exit, while the lighter oil would move in the secondary vortex towards the cyclone center. Dissolved oil particles and impurities, such as heavy metals would not be removed (Emmanuel, 6). In recent types, rotating cyclones have been developed. These cyclones function as both a hydrocyclone as well as a centrifuge. Rotating cyclones usually have higher removal effectiveness than the static hydrocyclone. Down-hole separation for oil can be described as a technique where the production of a water-oil mix at the base of the production well is separated through a hydrocyclone. The separated water is inserted into an appropriate underground zone while the remnant oil and water mix is transported to the surface. Thus, the quantity of water produced can be decreased by over fifty percent. This would result in a greater oil production, a fairly low water production as well as the utilization of lesser chemicals. The treatment and discharge of the water produced is significantly decreased.

Question 2

ECONOMIC EVALAUTION

From the data obtained from the excel sheet the summary table was obtained.

cum oil cum CAPEX cum OPEX $/bbl

Decline Base Case 106 100 1564 15.69

Refurbish GAZELLE & FSO 253 0 0 0.00

Replace GAZELLE complete and Pipeline 266 0 0 0.00

Replace GAZELLE & FSO (no pipeline) 266 0 0 0.00

From the table obtained, the cum oil during the refurbishment and replacement processes increased against the decline base case. They was also no cum CAPEX and Cum OPEX during the refurbishment and replacement exercises.

Question 3

FLOW ASSURANCE ISSUES

Flow assurance describes a relatively novel term in the oil & gas industry. Flow assurance denotes ensuring the economical and successful flow of crude oil from the reservoir to the sales point (Henry, 2005). Flow assurance issues are extremely diverse, encompassing several discrete as well as specialized subjects along with bridging the gap across various engineering disciplines. Flow assurance denotes the most serious task during deep-water crude oil drilling since the occur at high pressures and very low temperatures. The environmental and financial loss originating from production break down or asset destruction as a result of flow assurance accidents can be crippling. What makes flow assurance even harder is that these resource deposits can react together with one another and can cause deadly blockage in pipelines and cause flow assurance failure. An example of a flow assurance process is thermal pipeline investigation. Another example is the assessment of erosion as a result of the presence of sand particles in equipment.

For the refurbishment of the present system, old existing flow assurance measures should be utilized. Thermal investigation should be carried out. Also the pipeline pumping crude form the wells to the platforms should be constantly monitored to prevent leakages, which will cause oil spillage.

Replacement of the FSO with pipelines carries significant risks. The pipelines need to significantly monitor to ensure no leakage. Also the pipelines used must meet standard specifications to ensure that they do not rupture as a result of excessive pressure. There are several methods of handling the flow assurance concerns in offshore pipelines and installations. A most commonly utilized method is to apply particularly designed flow assurance coverings on the pipe as well as field joint area. In the oil industry, many flow assurance coatings manufacturers employ a “one size fits all” methodology by offering only particular types of coatings for flow assurance irrespective of the project design parameters (such as water depth, maximum functioning temperature and method of installation). This type of flow assurance coatings will not be used for pipelines in option 2. The coatings used will provide end to end anti-corrosion as well as flow assurance systems, which will include the factory fitted line pipe coating along with a highly functional field joint coating. An end to end flow assurance coating mechanism offers significant merits to the offshore-pipeline operators as well as contractors. Operators will obtain definite long-term thermal performance assurances for the complete pipeline operation, an optimized thermal design that enhances the pipeline performance. The only drawback of this is that it comes at added costs.

With complete system replacement comes novel problems and flow assurance issue. The new system must be properly evaluated to ensure no unexpected or foreseen problems.

Question 4

The three options are viable options and will be evaluated based on risk of environmental pollution and present manpower available to implement this system. They first option entails the refurbishment of the FSO as well as the addition of a centrifuge system. This system is very viable and the present gazelle staff can be trained on how the centrifuge system functions. The present gazelle staff already know how to use the FSO system hence adapting to the new system will be easier.

The second option involves changing the process to using an appropriate pipeline system where pipes are installed and used to perform the function of FSO. This system is viable but the implementation costs are very high. The amount of money to be spent on the pipes will be high and the staff will need to be trained on how to use the pipelines. This will take time and errors will exist. Using pipes also pose risks, since leakages easily occur from pipelines cause significant environmental degradation.

The third option involves changing the whole system. A new FSO unit will be bought and installed. This system will use Hydro-cyclones and Down-Hole separation in conjunction with pipes for the purification of contaminated water. The system is costly, will require intensive training of the staff, and will cost more money. Also the risks from the pipelines are very high. The can easily be ruptured and environmental pollution will occur.

Question 5

My recommended developmental option is option 1. Option 1 has been successful since the creation of the Gazette offshore oil field. The refurbishment will revitalize the already existing system. The centrifuge system will be integrated to ensure that the generated waste water is treated to meet environmental standards before disposal. Using pipes to replace the FSO will work but this pipes will be expensive to install and can easily rupture causing severe environmental degradation at very high costs.

Decommissioning outline for option 1

Injection and production wells

Downhole equipment for example the tubing inside the wells would be removed while the perforated segments of the wellbore along the reservoir will be cleaned of scale, sediment and other form of debris. The remaining hydrocarbons in the production wells would be displaced using weighted brine and the wells would be cement plugged to inhibit fluid migration from the wellbore to overlying formations or the seabed. The subsea trees would also be removed while the wellheads would be about 4m above the seabed. These wellheads would have water depths of between 1,100 m and 1,600 m. They will not serve as a hindrance to fishing or navigation activities in the future. The precise decommissioning requirements would differ slightly for each well. The wells would be abandoned individually using a well service vessel or drilling rig.

Decommissioning the FSO

The FSO would be detached from the risers as well as the production system separated from the wells. Equipment, which are topsides, would be decommissioned offshore. Production system would be washed from the FSO end with the aid of seawater to remove any residual production fluids and oil. The flushing water would be returned back to the FSO for treatment. The remaining hazardous waste would be carried to shore as well as treated at a suitable approved waste treatment plant. After the system for production has been flushed as well as confirmed clean, the FSO would be released for removal from the mooring-system.

The final disposition of the FSO would be based on its current condition at the conclusion of production and upon the other options available for future use. When the decision is to decommission the FSO, it would be moved from the production site to a location where it would be dismantled or scrapped based on the adequate international conventions. Based on the state of the FSO it may be refurbished as well as re-used at other sites (Adedayo, 6). The mooring system chains and lines would also be recovered.

Subsea Facilities

Subsea facilities, which lay above the seafloor, would be removed. The flexible risers up to the FSO would be disconnected from the bases and recovered through reeling onto the lay vessel. Umbilicals would be recovered and the termination boxes along with other subsea important control equipment. Subsea manifolds, production as well as wellhead jumpers will be recovered to the surface after flushing while any steel piles used to support the subsea equipment will remain in-situ and protrude a maximum of about one to three meters above the seabed within waters bodies between 1,100 m and 1,600 m deep.

Wastes and discharges, which occur in the course of the decommissioning, will satisfy the same discharge standards that applied during the operational stages of the project (Climate and Pollution Agency 15). After abandonment of the subsea facilities and wells a seabed survey would be carried to check the effectiveness of this abandonment process.

WORKS CITED

Adedayo, Ayoade. Environmental Risk and Decommissioning Of

Offshore Oil Platforms in Nigeria. NIALS Journal of Environmental Law. 2011. Pdf

Climate and Pollution Agency. Decommissioning of offshore installations. Oslo. 2011. Pdf

Emmanuel, Philip. Using Advanced Water Protection systems in the Niger Delta Area of Nigeria. Lagos: Universal, 2008. Print

Henry, Marcus. Flow Assurance Processes. Lagos: Universal, 2005. Print

Kumasi, Hart. Flow assurance guidelines. Accra: Essien, 2006. Print

Mollard, F and Robert, C. Floating LNG: the challenges of production systems and well fluid management. n.d. Web. 12 Nov 2013

Ojo, K. Water processing systems. Abuja: Wilford, 2009. Print

Samson, Hyacinth. Separation Techniques. Lagos: Universal, 2004. Print