Subsea Challenges in North Sea Projects
Subsea oil production is becoming a popular method for exploring undeveloped oilfields located under the sea. Though there are several subsea oil projects in the world, the huge amount of resources required has left many subsea oil fields unexplored. Some of the technical challenges experienced in large subsea oil development projects such as Rosebank include long tiebacks, Sustained Casing Pressure (SCP), erosion-corrosion of the flow facilities and flow assurance problems such formation of hydrates and deposition of scales and wax along the flow lines and pipelines. This dissertation seeks to explore different technical challenges experienced or likely to be experienced during design, implementation and operation of the Rosebank oil production project in the UK. Rosebank project is located about 130 kilometres in the North-West of Shetland-Islands at a depth of about 1.1 kilometres. The gas line is expected to join the Sirge Pipeline located about 236 kilometres from Rosebank.
The obtained results indicate that large project size and undersea location increases the overall project complexity, hence the magnitude of the technical challenges faced. It was found that formation of hydrates and scale can be reduced through insulation and use of thermodynamic inhibitors such as alcohol and glycol. It was also noted that SCP is a serious challenge in subsea oil projects since it may easily lead to complete shutdown of the plant if not addressed in time. Some of the technologies used to remedy SCP once detected include the rig method and the rigless method. It was further established that the presence of sand particles in fluids combined with corrosion action induces a substantive amount of wear with time. To remedy the situation, it is necessary to employ the available technologies such as disanding cyclones and hydro-cyclones
TABLE OF CONTENTS
LIST OF FIGURES. vi
LIST OF TABLES. vii
LIST OF ABBREVIATIONS. viii
- EXTENDED INTRODUCTION.. 1
1.1 Research Background. 1
1.2 Research Problem.. 3
1.3 Aims and Objectives. 4
1.4 Review of Literature. 4
1.4.1 Flow assurance. 5
1.4.2 Sustained casing pressure (SCP) 9
1.4.3 Maintenance challenges. 11
- METHODS AND RESULTS. 12
2.1 Research Methods. 12
2.1.1 Research questions. 12
2.1.2 Hypothesis statement 13
2.1.3 Research design. 13
2.1.4 Data collection. 15
2.1.5 Data analysis. 16
2.1.6 Accuracy and effectiveness of the research method. 16
2.2 Results. 17
2.2.1 Quantitative results. 17
2.2.2 Qualitative results. 21
- DISCUSSION AND CONCLUSIONS. 23
3.1 Discussion. 23
3.1.1 Project location and size as a challenge. 23
3.1.2 Complexity of the Rosebank project 24
3.1.3 Technical challenges-operation stage. 26
3.2 Discussion of Qualitative findings. 28
3.2.1 Solutions to the challenges. 29
3.3 Conclusions and recommendations. 30
3.3.1 Conclusions. 30
3.3.2 Recommendations. 31
LIST OF FIGURES
Figure 1‑1 Map showing the location of the Rosebank project and the Sirge Pipeline (Chevron, 2014) 2
Figure 1‑2: Schematic diagram of a typical GRA scanner in operation (Davies, 2009) 6
Figure 1‑3: Normal temperature profile – no leakage (Inaudi & Glisic, 2010) 7
Figure 1‑4: Measure temperature profile – with leakage (Inaudi & Glisic, 2010) 7
Figure 1‑5: CAD drawing of smart-pipe that uses optic fibre tape to detect blockage or leakage (Inaudi, & Glisic, 2010) 8
Figure 1‑6: SCP build-up – normal pattern (Zhu, et al., 2012) 9
Figure 1‑7: SCP build-up – S-shaped pattern (Zhu, et al., 2012) 10
Figure 3‑1 Complexity percentage score for different project stages. 25
Figure 3‑2 Technical challenges facing the Rosebank project 26
LIST OF TABLES
Table 2‑1 Project location and size as a challenge. 17
Table 2‑2 Complexity of the Rosebank oil development project at design, installation and operation stages 18
Table 2‑3 Potential challenges likely to be faced during operation. 19
Table 2‑3 Chi-square test results between design complexity and project size and location. 19
Table 2‑4 Chi-square test – Installation complexity and variables, project size and location. 20
Table 2‑5 Chi-square test results between operation complexity and project size and location. 20
LIST OF ABBREVIATIONS
||Sustained Casing Pressure
||Gamma Ray Absorption
||Flow Assurance Program
||Floating Production, Storage and Offloading
||Remote-Operated inspection Vehicles
||Autonomous Underwater inspection Vehicles
||Remote-Operated inspection Tools
||National Agency of Petroleum
1. EXTENDED INTRODUCTION
1.1 Research Background
The quest for increased oil and gas supply has triggered the need to explore different types of oil fields both on land and under the sea. Though both subsea and land oil development projects require huge financial and technical input, subsea projects have been found to be more challenging depending on size and location (Crook, 2010). In most cases, subsea oil production challenges are experienced due to complexity of various processes including design, installation and operation. Some of the technical challenges experienced in large subsea oil development projects include long tiebacks, Sustained Casing Pressure (SCP), erosion-corrosion of the flow facilities and flow assurance problems such formation of hydrates and deposition of scales and wax along the flow lines and pipelines.
According to Markeset et al. (2013), the complexity of subsea oil production projects is depicted in processes such as multiple drilling, design and installation of multiphase pumping systems and positioning of the Floating Production, Storage and Offloading units (FPSOs). One of the biggest subsea oil production projects in the world is the Rosebank oil development located in the UK. This project seeks to explore different technical challenges experienced or likely to be experienced during design, implementation and operation of the Rosebank oil production project. In addition, the project further establishes possible solutions to the identified challenges. To accomplish this, a literature review has been carried out followed by collection and analysis of relevant primary data.
Chevron (2014) indicates that the Rosebank project is located about 130 kilometres in the North-West of Shetland-Islands at a depth of about 1.1 kilometres. The gas line is expected to join the Sirge Pipeline located about 236 kilometres from Rosebank. The Sirge Pipeline starts at Sullom Voe and stretches all the way to St. Fergus terminal. The map shown in figure 1-1 below shows the actual location of the Rosebank project and the Sirge pipeline.
Figure 1‑1 Map showing the location of the Rosebank project and the Sirge Pipeline (Chevron, 2014)
Due to the huge amount of resources required, the project is being undertaken jointly by three major oil production firms namely Chevron UK, Dong Energy Denmark and OMV UK. However, the FPSO unit to be employed in the project will be designed and built by the Hyundai Industries Korea.
1.2 Research Problem
Being a huge subsea development, the Rosebank project is likely to face serious technical challenges throughout the entire project lifecycle. As at the moment, the project has been experiencing a number of challenges in the design phase. At some point, the main stakeholder, Chevron questioned the economic viability of the project due to the high initial capital (Chevron, 2014). Since strict design requirements have to be met by the design team, technical challenges are not only experienced during installation but also at the design stage. The huge size of important facilities may make it difficult to achieve efficient primary cementing, leading to the accumulation of SCP in the system. If this happens, flow of fluid in the pipelines may be affected, leading to inefficient production. In addition, the increased sea depth means that long tiebacks have to be used. This may reduce flow efficiency and increase power consumption due to energy loss along the flow lines. It is also worth noting that long tiebacks increases the chances of hydrate formation and scale deposition, meaning that flow assurance may be affected.
The presence of many pipe fittings within the system encourages solid particulate accumulation leading to blockages. According to Pearce et al. (2013), sand particles are the main solid particulates that encourage blockages in subsea oil development projects. Sand particles may also cause accelerated erosion-corrosion pipe wear due to combined effects of abrasion and corrosion. The temperatures at the seabed may be as low as 40C, meaning that wax can be cooled to form a thick gel on the surfaces of the pipelines. Continued accumulation of the gel may result in restricted flow, an effect that may lead to system failure due to increased pressure.
Though the above challenges have generally been found to affect subsea projects, no study has been carried out on the Rosebank project to establish the impacts of the challenges on the final project outcome. Since every project has distinct technical challenges depending on environmental conditions, capacity and location, it is difficult to clearly understand the challenges facing the Rosebank project without conducting primary research. Finally, in order to suggest viable technical solutions to different types of challenges, it is necessary to understand the possible causes of the challenges and their relationship with different project characteristics.
1.3 Aims and Objectives
This research project aims to explore different technical challenges experienced or likely to be experienced during design, implementation and operation of the Rosebank oil production project. Also, the project further aims to find possible solutions to the identified challenges. Ultimately, the study shall work towards achieving the following three objectives:
- To establish the influence of subsea project size and location on the complexity design, installation and operation processes.
- To identify and evaluate the level of severity of different technical challenges on the operation of the Rosebank project
- To find viable solutions to the identified technical challenges facing the Rosebank project
1.4 Review of Literature
Subsea oil development projects are faced by a number of technical challenges including flow assurance and SCP. Flow assurance is affected by problems such as wax and scale deposition, hydrate formation and erosion-corrosion of flow facilities such as flow lines and pipelines.
1.4.1 Flow assurance
Unrestricted flow of gas and oil streams in a subsea oil production facility is highly important. Kondapi (2015) conducted a study on the factors that affect flow assurance in a subsea project and noted that formation of hydrates, wax deposition, erosion-corrosion and scale deposition were the main causes of blockages. The author pointed out that to address the above challenges, a method of identifying and quantifying each of the causes along the entire system is required. However, Chew (2014) noted that it can be difficult to identify floe problems along the system especially when they are at the early stages. According to the author, the process of identification is affected by the changing production profiles, system pressure and temperature.
Schwing et al. (2015) established that subsea temperatures may fall as low as 40C at about 61 meters (2000 feet). Since the Rosebank project depth is about 1100 meters, which is far much higher than above depth, the temperatures at the subsea may even fall below 40C depending on the weather. Ginsburg and Thomas (2015) were able to show that when temperatures of the fluids fall to 40C and below, transportation of crude oil may become a challenge due to gell formation. In a different study Love et al. (2011) established that pressure changes within the flow system can destabilize asphaltenes contained in oil, thus causing plugging. Formation of hydrates is another common cause of restricted fluid flow in oil and gas pipelines. The icy clusters are formed due to interaction between methane gas and water. Accumulated amount of hydrates may choke or completely prevent fluid flow thus impairing the performance of the flow system. As established by Chew (2014), the presence of sand particulates in the flow system results in surface erosion due to abrasion. When combined with the effects of corrosion, the resultant erosion-corrosion wear may be highly pronounced.
To ensure that unrestricted flow is experienced throughout the system, different solutions need to be adopted. Ginsburg and Thomas (2015) argue that the best solution is to develop a blockage detection method so that any flow restrictions can be detected at early stages. However, detection of blockages alone may not yield promising results if an action to control the cause of the blockage is not attempted. Love et al. (2011) noted that blockage detection can be realized through the use of pipe scanners based on Gamma Ray Absorption (GRA). A typical GRA scanner utilizes a source of weak gamma rays to provide information about the interior of the system. Davies (2009) explains that due to the high accuracy of gamma rays, the exact location of such deposits can be determined. A schematic diagram of a typical GRA scanner in operation is shown in figure 1-2 below.
Figure 1‑2: Schematic diagram of a typical GRA scanner in operation (Davies, 2009)
Blockage can also be detected using fibre optic. This method employs a sensor that provides information about temperature distribution along the pipeline to detect flow restrictions along the system. To detect a leakage or blockage, the normal temperature profile is compared with the measured profile as shown in figure 1-3 and 1-4 respectively. .
Figure 1‑3: Normal temperature profile – no leakage (Inaudi & Glisic, 2010)
A change in temperature profile such as that shown in figure 1-4 is used to detect the presence of a leakage or blockage in the pipe.
Figure 1‑4: Measure temperature profile – with leakage (Inaudi & Glisic, 2010)
Such a technique was demonstrated by Inaudi and Glisic (2010), who developed a HDPE (High-density poly-ethylene) smart-pipe consisting of embedded optic fibre tapes, used to monitor fluid flow through the pipe. A CAD drawing of the smart-pipe is shown in figure 1-5 below.
Figure 1‑5: CAD drawing of smart-pipe that uses optic fibre tape to detect blockage or leakage (Inaudi, & Glisic, 2010)
Though this technology has been proved to be highly reliable, its large scale application is rather difficult. This is because the fibres need to be embedded inside the pipes. The technology depends on Joule effect, since the presence of a flow restriction lowers pressure and increases flow velocity and temperature.
While trying to address the root-cause of pipe and flow line blockage, Franchek (2015) argues that formation of hydrates can be reduced using insulation. Insulation preserves heat thus keeping the temperatures far from the temperature range within which hydrates form. Though this is a reliable method, it is only possible for short flow lines. Since Rosebank project will have long flow lines, advanced insulation systems may be required. It has also been shown that scaling and hydrates formation processes can be lowered through the use of thermodynamic inhibitors. Some of the most common inhibitors employed in the subsea include alcohol and glycol.
1.4.2 Sustained casing pressure (SCP)
Ellerton and Roberts (2014) explain that SCP occurs when casing pressure rebuilds blending off. The build-up process may assume two main patterns: the normal pattern and the s-shaped pattern (Zhu, et al., 2012). The normal pattern is noted when SCP starts building rapidly after bleeding off and later stabilises after reaching a maximum value as shown in figure 1-6 below. A build-up process that assumes this pattern is considered highly dangerous, since the growth rate remains relatively high at the early stages. In most cases, detection occurs when the process is in the transition or later stages.
Figure 1‑6: SCP build-up – normal pattern (Zhu, et al., 2012)
When SCP build-up follows the S-shaped pattern, casing pressure drops rapidly during the early stages, but later increases rapidly towards the transition zone. As time goes by, casing pressure reaches a maximum value and stabilises as shown in figure 1-7.
Figure 1‑7: SCP build-up – S-shaped pattern (Zhu, et al., 2012)
The above build-up process can be detected and controlled easily as compared to the normal pattern.
Ellerton and Roberts (2014) enumerates a number of problems that may be experienced due to the presence of SCP at the wellhead. These include pollution of the environment, blowout in the worst case, damaged safety valves and cement integrity. In a research by Duan,et al. (2013), it was found that SCP is among the most common causes of subsea systems failure.
The problems associated with SCP can hardly be eliminated; however, some technologies have been developed to detect and remediate the problem. As pointed out by Crook (2008), it is relatively difficult to access the affected annuli due to their hidden locations. According to the author, the cost of repairing a system affected by SCP may be too high, making work over the best option. Remediation of SCP in a typical subsea project is carried out using two methods, namely the rig method and the rigless method. When rig method is employed, a special rig is physically moved to the affected zone to relieve the pressure. On the other hand, injection of high density liquid is carried out onto the affected zone to relieve the pressure.
1.4.3 Maintenance challenges
Failure of subsea systems is one of the greatest challenges encountered during underwater oil production (Moreno-Trejo, & Markeset, 2012). To lower the probability of failure, oil companies have tried several strategies aimed at improving their performance in terms of system maintenance. Basically, subsea systems fail due to poor installation, overload, excess stresses, corrosion, fatigue and cracking. These causes are triggered by environmental factors, operating conditions and design flaws. Some of the remediation methods include the use of Remote-Operated inspection Vehicles (ROVs), Remote-Operated inspection Tools (ROTs) and Autonomous Underwater inspection Vehicles (AUVs). The inspection vehicles are unmanned and therefore can be operated over a long period of time to ensure that all the system components have been inspected properly. As pointed out by Almasi (2012), unmanned inspection vehicles are used to run integrity maintenance programs in the subsea.
2. METHODS AND RESULTS
This chapter presents the research methodology adopted by the researcher and the results obtained after the implementation of the methods. The chapter has been divided into two main sections, namely the methods section and the results section. The methods section describes the research approach adopted by the researcher to design the instruments of data collection, the process of data collection and methods of data analysis employed. On the other hand, the results section summarizes the data obtained by the researcher and the results of analysis. Apart from presenting the results, this section further interprets the results while taking into consideration the stated research objectives.
2.1 Research Methods
According to Venkatesh et al. (2013), research methods are tools used by the researchers to derive correct answers to the research questions. As argued by Zachariadis et al. (2013), the obtained solutions should be justifiable. As such, the reliability of the final results of a given research is highly dependent on the employed research methodology. It is therefore important to ensure that the best methods are selected prior to the initiation of the process of data collection.
2.1.1 Research questions
This project has adopted the most suitable research methods based on the two major research questions stated below.
- What are the technical challenges facing the Rosebank oil project?
- What are the solutions to the identified challenges based on expert knowledge?
As pointed out by Silva et al. (2014), research questions should seek to assess all details of the research problem. As such, questions that appear to be general should be supported using more specific minor questions. Therefore, to further enhance the investigation of the research problem, three minor research questions were developed to support research question 1.
- How challenging is the Rosebank project owing to its large size and location?
- What is the level of complexity of the Rosebank project in relation to the following: design, installation and operation?
- How severe are different technical challenges likely to face the Rosebank project during operation?
2.1.2 Hypothesis statement
It has been argued that further interpretation of research findings can be enhanced through hypothesis testing (Zachariadis, et al., 2013). In this project, it was considered necessary to investigate the relationship between the complexity of the project and the variables, size and location. The following hypothesis will therefore be tested:
“There exists a significant association between project size and location and the complexity of the Rosebank project.”
2.1.3 Research design
A research study can be designed in accordance with three main approaches: quantitative, qualitative and mixed approach. While quantitative approach is based on quantifiable numerical data, qualitative approach is based on textural data (Venkatesh, et al., 2013). An overview of the research questions stated herein reveals that the major question requires qualitative answers while the minor questions can only be answered quantitatively. In this regard, a mixed approach was adopted in the project.
The project depends on primary data collected using two instruments: the questionnaire and the interview. The questionnaire was designed to collect quantitative data from the selected participants, while the interview was used to collect qualitative data from the selected respondents. In terms of design; the questionnaire was divided into two major sections (sections A and B) and one minor section (cover letter). Section A aimed at collecting personal information of the participants including the name of company, nature of work, job role, experience and academic qualification. Section B (Questions 7-9) was developed to collect the main research data in relation to challenges facing the Rosebank project.
Q-7 Kindly indicate how challenging is the Rosebank project due to increased project size, offshore distance and depth. Please use the following scale:
Q-8 Based on your own assessment, what is the complexity of the Rosebank project at different stages? Please use the scale below:
Q-9 Please assess the listed challenges in terms of severity on the performance of the Rosebank project. Use the scale below:
On the other hand, the interview consisted of two questions, both designed to provide answers to the major research questions. The two questions are shown below.
Q-1 In your opinion based on your knowledge and experience in subsea oil field development, what are the main technical challenges facing the Rosebank project?
Q-2 What do you think can be done to address the challenges prior to project initiation?
2.1.4 Data collection
Since there were two data collection instruments already designed, two distinct methods were employed to collect the required data. To begin with, quantitative data was gathered through an electronic survey. Participants were identified and contacted through social and professional networks namely Facebook and LinkedIn. Specifically, 48 potential participants were contacted, most of whom were employees at Chevron UK, Dong Energy Netherlands and OMV UK. However, only 28 participants agreed to participate in the study. Finally, out of the 28 participants, only 18 returned their feedback within the recommended duration.
On the other hand, interviews were conducted with only three respondents. The respondents were engineers at Chevron. Efforts were made to conduct more interviews but due to time limitations, only a few respondents were contacted, from which three agreed to participate in the study.
2.1.5 Data analysis
The raw data collected using questionnaires was manually entered in an excel sheet and later exported to SPSS for analysis. SPSS is a statistical software tool with multiple in built analysis features hence preferred in this project. Basically, the analysis was carried out through computation of mean, standard deviation and data range. Testing of hypothesis was carried out using descriptive statistics in which Chi-square test was performed. As stated by Garrison et al. (2013), two variables are associated only if the two sided Pearson significance value is less than 0.05. On the other hand, Qualitative data obtained from interviews was analyzed using a deductive approach (Girvan, & Savage, 2012).
2.1.6 Accuracy and effectiveness of the research method
With regard to quantitative data, a relatively small sample (18 participants) was analyzed. According to Venkatesh et al. (2013), the accuracy of quantitative data is higher for larger samples and lower for smaller samples. However, the accuracy is also dependent on the knowledge and experience of the participants on the subject under investigation. Owing to the fact that only experienced engineers, technicians and technical managers from the involved companies were involved in the study, it can be argued that the obtained data is fairly reliable and accurate. Also, 18 feedbacks can be concluded to be sufficient for analysis, since specific data trends can be observed. Finally, since the required data was collected and analyzed successfully, it can be inferred that the employed research methods were effective.
This section presents the analyzed data followed by a brief interpretation of important aspects based on the research questions. For clarity purposes, quantitative and qualitative results have been presented separately.
2.2.1 Quantitative results
22.214.171.124 Increased offshore distance and sea depth
The participants were asked to indicate how challenging the Rosebank project was, owing to the long offshore distance and increased depth. The answers provided by the participants were organized, analyzed and the results included in table 2-1. The table shows that on average, increased offshore distance and depth generally makes the Rosebank project very challenging. The project scored an average of 4.33 out of 5, which translates to about 87 percent. The small data range and standard deviation imply that the participants had fairly similar opinions regarding the matter.
Table 2‑1 Project location and size as a challenge
Based on the findings, it can be asserted that increased offshore distance and sea depth constitute one of the most important factors that make the Rosebank project very challenging both economically and technically. However, this project is only concerned with technical challenges facing the Rosebank project.
126.96.36.199 Complexity of the project
In order to evaluate the complexity of the Rosebank project at different stages, the participants were asked to assess three main project stages, namely the design stage, the installation stage and the operation stage. The data collected from the participants was organized, analyzed and the results included in table 2-2. Based on the results shown in the table, the three stages including design, installation and operation scored between 3.67 and 4.44 on average. This translates to a percentage mean score of between 73 percent and 89 percent.
Table 2‑2 Complexity of the Rosebank oil development project at design, installation and operation stages
It can be argued that all the three stages of the Rosebank project are very complex. The small data range and standard deviation suggest that the participants did not have varying views..
188.8.131.52 Evaluation of identified challenges
Through literature review, six potential challenges that may have a negative impact on the Rosebank project were identified and evaluated by the participants (see table 2-3). From the table, it can be seen that all the challenges are severe. The data shows that blockage of flow lines was identified as an extremely severe challenge, while leakages and failure of safety valves, a very severe challenge. From the lower end of the scale, SCP was identified as the least severe challenge among the six challenges. Though the above challenges can only be experienced during project operation, it is worth noting that the challenges are as a result of difficulties experienced during design and implementation stages.
Table 2‑3 Potential challenges likely to be faced during operation
|Formation of hydrates
|Deposition of scales and wax
|Corrosion of pipelines
|Blockage of flow lines
|Leakages and failure of safety valves
|Sustained casing pressure (SCP)
184.108.40.206 Testing of hypothesis
Three tests were performed to validate or reject the stated hypothesis. Project complexity was divided into three minor variables, namely design complexity, installation/implementation complexity and operational complexity. Each of the variables was tested against the main variable (increased sea depth and offshore distance), through Chi-square analysis.
To begin with, the test between design complexity and increased sea depth and offshore distance produced a Pearson 2-sided significance P, value of 0.0017, a likelihood ratio (LR) of 0.045 and a linear-by-linear association (LLA) of 0.027 (see table 2-3 below).
Table 2‑3 Chi-square test results between design complexity and project size and location
||Asymp. Sig. (2-sided)
100.0% cells have expected count less than 5. The minimum expected count is .11.
Focusing on the value of P, which fulfils the requirement P<0.05, it can be argued that there is a strong relationship between design complexity and increased sea depth and offshore distance.
In the second test, Chi-square analysis was carried out between installation complexity and increased sea depth and offshore distance and the results summarized in table 2-4. From the table, , and .
Table 2‑4 Chi-square test – Installation complexity and variables, project size and location
||Asymp. Sig. (2-sided)
100.0% cells have expected count less than 5. The minimum expected count is .11.
Based on the results, the obtained value of is less than the critical value of 0.05. Therefore, it is evident that there exists a significant association between installation complexity and variables, project size and location. In the third test, Chi-square analysis was performed between operation complexity and increased project size, sea depth and offshore distance and the results included in table 2-5.
Table 2‑5 Chi-square test results between operation complexity and project size and location
||Asymp. Sig. (2-sided)
From the table, and. This implies that there exists a strong relationship between operational complexity and variables, location and increased project size. It can therefore be concluded that hypothesis was valid in all cases, hence accepted. This leads to the conclusion that increased project size, sea depth and offshore distance highly contribute to Rosebank project complexity.
2.2.2 Qualitative results
220.127.116.11 Challenges facing the Rosebank oil and gas project
According to the respondents, the large size of the project is the most pressing challenge. One of the respondents stated “The size of this project is relatively large compared to other subsea projects in the area. The Rosebank FPSO is one of the largest in the world.”
It was also pointed out that the large sea depth is a great challenge to the designers. Combined with the large size of the project, increased sea depth complicates the design requirements thus making it difficult to achieve high efficiency. According to one of the respondents “the large sea depth not only increases design complexity but also increases the probability of hydrate formation, scale deposition and corrosion of the installed pipelines”. Other challenges identified by the respondents include:
- Restricted flow/flow assurance
- Low sea bed temperatures
- Sand accumulation
- Waste disposal problems
- Complexity of the safety features
18.104.22.168 Solutions to the challenges
The respondent suggested different methods that can be used to address the identified challenges. They argued that though careful design can eliminate future challenges when the project is in operation, some problems can only be eliminated or minimized through proper maintenance. The following solutions were suggested
- Adoption of intelligent completions
- Implementation of a flow assurance system
- Adoption of down-hole technology
- Early SCP detection and bleeding off
- Use of well designed desanding cyclones and hydro cyclones
- Sand cleaning before disposal
- Adoption of a vigorous design testing program
A detailed discussion of the results presented in this chapter will be carried out in the next chapter.
3. DISCUSSION AND CONCLUSIONS
The first section of this chapter reviews and expounds the findings presented in the previous chapter in relation to the reviewed literature. The second section summarizes the main findings of the research and states the main conclusive remarks for every research question. Finally, the section gives a summary of recommendations for further and future technical action.
3.1.1 Project location and size as a challenge
The size and location of a subsea oil development project in terms of sea depth and offshore distance highly affects the oil and gas production process (Pearce, et al., 2013). According to Chew (2014), increased sea depth and offshore distance increases the amount of infrastructure resources required and further complicates the oil production process. Since very long pipelines have to be employed, technical challenges such as hydrate formation, wax deposition and corrosion due to sand abrasion become inevitable. Logically, larger subsea oil projects are more challenging to carry out compared to small scale projects. As argued by Crook (2010), large subsea oil projects are not only complex in terms of design, but also challenging in terms of implementation and operation.
In the results presented in the previous chapter, it was found that project location and size highly contribute to the level of complexity of subsea projects. According to Chevron (2014), Rosebank oil and gas production project is located at about 130km North-west of Shetland Island. During processing, products will have to be pumped using a multi-pump system over a depth of more than 1.1km from the sea bed. Again, based on the map shown in figure 1-1 in the introduction chapter, the gas will have to be transported for a distance of about 236km in order to be tied to the existing Sirge pipeline. The above description makes it clear that Rosebank project location may not be favourable for oil production. This means that the stakeholders need to put more efforts to ensure that the existing challenges are addressed as the project progresses from design to implementation and finally to operation.
3.1.2 Complexity of the Rosebank project
As asserted by Crook (2010), the complexity of a subsea oil development project is usually depicted in each stage of the overall life cycle. Rosebank project will involve the use of one of the largest FPSOs in the world, designed and constructed by the Hyundai industries. This implies that all other infrastructural facilities and machinery will be of a similar scale in terms of size. In addition, the project is expected to run for a relatively long period of time meaning that the designed systems should have a relatively high reliability. Past research has shown that most subsea systems do not operate for more than five years without having to undergo heavy maintenance and component replacement (Markeset, et al., 2013). It can therefore be argued that the Rosebank project design team has a big challenge, since the designed systems are expected to meet high-end specifications.
According to the results presented in the previous chapter, the installation/implementation stage was identified as the most complex stage of the Rosebank project with a score of about 89 percent. To enhance clear illustration of the findings the bar chart shown in figure 3-1 below was produced using the results shown in table 2-2 in the previous chapter.
Figure 3‑1 Complexity percentage score for different project stages
The percentage scores were obtained by converting the mean score into percentage form using the formula: where, is the mean score shown in table 2-2 in the previous chapter. The chart shows that though implementation was identified as the most complex stage, other stages were also ranked complex. The findings are in agreement with past research studies by (Marotta, 2015; Suardin, et al., 2009; Schwing, et al., 2015).
The results obtained during hypothesis testing showed that complexity of the Rosebank project in terms of design, installation and operation can be attributed to the large project size and unfavourable location. It has been shown that oil development projects carried out on the sea bed have a high probability of failure (Love, et al., 2011). In addition, Ginsburg and Thomas (2015), pointed out that when a project becomes extremely complex in terms of implementation, the capital cost required to complete the project may be prohibiting. This is because such projects may end up being uneconomical based on a cost benefit analysis. According to Franchek (2015), any project that fails to recover the initial capital within a period of five years should be thoroughly evaluated to avoid unrecoverable losses. Though there has been no specific data based on a cost benefit analysis, major stakeholders such as Chevron have expressed their fears on the economic performance of the Rosebank project (Chevron, 2014). However, from the data provided by UK authority, the project will be successful, since the site has been proven to have the potential to produce a huge amount of oil and gas (Ellerton, & Roberts, 2014).
3.1.3 Technical challenges-operation stage
Based on the results presented in the previous chapter, Rosebank project will be faced by a number of technical challenges during operation. Due to the large size of processing systems employed in the project, challenges such as formation of hydrates, corrosion of pipelines, leakages and SCP are likely to be encountered. Based on the obtained results (see figure 3-2), it is clear that blockage of flow lines is the most severe challenge followed by leakages and formation of hydrates. As noted by Franchek (2015), the presence of solid particulates such as sand results in progressive pipe wear, thus reducing the lifespan of the pipework.
Figure 3‑2 Technical challenges facing the Rosebank project
In addition, such particulates may accumulate at particular parts of the pipework, thus interfering with oil or gas flow. Lin et al. (2013) stated that accumulation of solid particles usually occurs at the points where pipe fittings are used. Continued accumulation may lead to complete blockage of the pipework. The rate of accumulation of such particulates is dependent on the volume of oil being pumped and the effectiveness of the filtering process deployed at the seabed. Owing to the fact that Rosebank oil development is a large scale project, blockage of flowlines may be an issue of concern.
It is worth noting that blocked flowlines may encourage leakage due to increased fluid pressure between the point of blockage and the pump. Referring to figure 3-1, leakages and failure of safety valves is an extremely severe challenge with a score of about 82 percent. With regard to failure of safety valves, serious cases have been reported in different countries that have subsea oil plants. For instance, an explosion was experienced in a subsea oil development project in Brazil early this year (2015), where six workers were killed (The Chemical Engineer, 2015).
An investigation conducted by the National Agency of Petroleum (NAP) revealed that the explosion occurred in the pump house as a result of pipe burst due to increased pressure (Ellerton, & Roberts, 2014). According to NAP, the failure may have occurred due to blockage of pipework or failure of one of the safety valves installed within the pump house. It can therefore be argued that blockage of flowlines, SCP, leakages and failure of safety valves are severe challenges that may be faced during the operation of the Rosebank project. Other problems such as formation of hydrates, corrosion of pipelines and deposition of scales and wax may not be severe within a short period of time. However, in the long-term, such problems may lead to serious consequences including blockages of flow lines and leakages. It is therefore necessary to make sure that both design and implementation stages are carried out effectively to reduce the rate of corrosion, scale and wax deposition and formation of hydrates.
3.2 Discussion of Qualitative findings
The interview results presented in the previous chapter showed that the technical challenges facing the Rosebank subsea oil development project could be attributed to the large size of the project. In addition, the respondents indicated that restricted flow, low seabed temperature, sand accumulation, annular gas accumulation, waste disposal problems and complexity of safety features are the main challenges facing the Rosebank project.
Franchek (2015) noted that flow restriction due to blockages or annular gas accumulation is one of the most common challenges faced by large subsea oil projects. As discussed in the previous section, blockages occur due to accumulation of particulates around pipe fittings, corrosion, deposition of scales and wax and formation of hydrates.
Low seabed temperature results in gel formation when paraffin is cooled to a temperature of about 40C. This becomes a major problem since the risers and flow lines might be blocked. Pearce et al. (2013) asserted that the rate of gas accumulation may be increased due to poor installation of subsea facilities. Due to the large depth, the above causes may not be completely addressed, meaning that formation of annular gases may be an issue of concern. Lin et al. (2013) noted that waste disposal is a major challenge in subsea oil projects. In most cases, there are strict environmental regulations that govern waste disposal depending on the level of impact on the environment. Based on the views of the respondents, complexity of safety features such as safety valves is a major challenge to the Rosebank project. Lin et al. (2013) argued that safety features such as pressure relief valves should be highly reliable to avoid the occurrence of preventable accidents. Flapper and spring mechanisms are the most complex features of the safety valves, whose failure can result in severe consequences. The above discussed challenges can be addressed using appropriate procedures.
3.2.1 Solutions to the challenges
The respondents pointed out that the technical challenges likely to face the Rosebank project during operation can be addressed through the use of a reliable Flow Assurance Program (FAP). On similar grounds, Pearce et al. (2013) stated that the use of FAP can lower the probability of failure of different systems significantly. Basically, FAP should be at a position to identify potential risks such as blockages in time. The program should also quantify the identified risks and monitor blockage development to allow for the implementation of effective measures. Hydrate formation problem can be addressed through temperature control within the flow lines and risers. According to Franchek (2015), insulation of pipes can be employed as a method of enhancing heat retention within the system. Other methods that can be employed include down-hole water removal, controlled blow down and thermodynamic boundary alteration using alcohol.
Accumulated sand can be removed through the use of disbanding cyclones and disbanding hydrocyclones. The processes are geared towards the removal of sand particulates and hydrocyclones from the pipework (Ellerton, & Roberts, 2014). Finally, accumulated annular gases can be avoided by ensuring that sufficient cement coverage is used. In addition, proper primary cementing processes should be adopted throughout the process.
3.3 Conclusions and recommendations
Based on the results discussed in this project, it can be concluded that operation of the Rosebank subsea project will be highly challenging due to multiple technical challenges identified and discussed herein. However, by meeting the required project specifications, Chevron and other stakeholders can work through the project successfully. Since different technical challenges facing the Rosebank subsea project were identified and viable solutions suggested, it can be argued that the main aim of this study has been met. Similarly, all the stated study objectives were achieved satisfactorily.
From the results, it was found that the long offshore distance and large depth highly contribute to the overall project complexity, and hence the magnitude of the technical challenges faced. The above argument was confirmed by the results obtained after testing the main hypothesis. The level of complexity was found to vary slightly depending on the stage of the project. The results indicated that the installation stage was the most complex followed by the design stage and finally the operation stage. Since the challenges faced in the operation stage can be influenced by the quality of design and installation, it is necessary to ensure that the two processes are flawless.
Several technical challenges were identified and analyzed in the project including formation of hydrates, deposition of scales and wax, erosion-corrosion of pipelines, failure of safety valves and SCP. Since formation of hydrates and deposition of and wax is accelerated by the existence of low temperatures, they can be minimized through insulation. Insulation preserves system heat, thus keeping the temperature of the fluid outside the hydrates formation range. Also, it was found that formation of hydrates can be reduced through the use of thermodynamic inhibitors such as alcohol and glycol. It was noted that SCP is a serious challenge in subsea oil projects since it may lead to complete shutdown of the plant. Therefore, it is important to employ technologies that can detect SCP build-up so that remediation measures can be performed in time. Some of the technologies used to remedy SCP once detected include the rig method and the rigless method. It was further established that the presence of sand particles in the fluids combined with corrosion action induces a substantive amount of wear with time. If proper measures are not taken in time, the flow system may fail. To remedy the situation, it is necessary to employ the available technologies such as disanding cyclones and hydro-cyclones.
This project faced several limitations related to data availability and reliability. Though the study had targeted over 100 survey participants, the feedback turnout was less than 30 percent. In addition only three respondents were interviewed. To increase the number of participants, it is recommended that future work be designed such that the process of data collection is given sufficient time. Also, the project only studied technical challenges, and therefore the researcher had no chance to show how technical challenges translates to financial challenges. It is therefore suggested that future work on the Rosebank project be based on all types of challenges including financial, climatic, human resource and technical challenges.
Since Rosebank project is still ongoing, this dissertation recommends that strict measures be put into place to govern the design and installation of all project systems to avoid future problems when the project is in the operation stage. Most recent technology such as GRA, optic fibre among others should be embraced to detect blockages and other system problems in order to enhance quick action before the problem reaches the worst stage. Also, remediation processes such as insulation and use of inhibitors to reduce the formation of hydrates and wax should be used regularly to boost flow assurance.
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