Top of Line Corrosion (TOLC) occurs in deepwater wet gas systems when water vapor condenses on the upper internal walls of the flowline due to the heat exchange occurring between the hot fluid and the colder environment. The condensed liquid becomes enriched by the corrosive species naturally present in the gas stream and assumes a low pH because it does not contain any buffering species such as bicarbonate or iron. The predominant concern is carbon dioxide (CO2), which reacts with water to form carbonic acid (H2CO3), although hydrogen sulfide (H2S) and organic acids can also present significant challenges and drive the corrosion process.
A HAZOP is a team-based process hazard analysis (PHA) method. Its purpose is to identify hazards and operability issues in a process design. In some HAZOPs, identified issues are evaluated for risk. An effective risk assessment method allows the HAZOP participants and the project team to focus their time and energy on the more significant hazards.
Risk assessments in HAZOPs are typically performed using a simple risk matrix (Figure 2). In the risk matrix approach, participants make judgments as to the potential severity and the likelihood of an event. The combination of severity and likelihood indicates the risk. The risk matrix will often be color coded with green areas (OK), red areas (Unacceptable) and yellow areas (improvement suggested, subject to ALARP).
Standard Operating Procedures (SOPs) for oil and gas production facilities are typically written by teams of subject matter experts including at least process engineers and experienced operators. The team is tasked with identifying the most effective ways to operate the facility (based on safety, environmental protection and economic measures). Operating the facility consistently in accordance with the SOPs should yield considerable benefits.
Yet, despite their obvious importance, often relatively little effort goes into SOP development and use.
SOPs are frequently developed late in the project, after the design is completed and construction is well underway. They may be used for little other than operator training. Following the initial facility startup, they may even end up on a shelf collecting dust. In this environment SOPs have little influence on either the design or the operation of the facility.
Significant interest exists in the deployment of 13Cr martensitic stainless steels in offshore oil and gas projects. Several grades of 13Cr exist, with the seemingly negligible variations between their chemistries and fabrication processes. The different grades perform dramatically differently, especially regarding cracking resistance in sour or chloride-containing environments. Determination of the proper 13Cr grade for sour service involves the investigation of domain diagrams, and often requires further fitness-for-service testing. However, the validity of each domain diagram for only one chloride concentration or content greatly limits their practicality for selecting 13Cr, thus impeding the ability to determining if fitness-for-service testing should be performed and its potential outcome.
Concept selection and initial design of deepwater subsea production systems can have a profound impact on the evaluation of the commercial viability of a discovery. Although detailed design comes later in the process, the decisions made at this early stage of a project will generally provide the template that is carried through to construction and operation. Scale management can be a significant factor in deciding the outcome of the concept selection phase, particularly for fields that are expected to require seawater injection at some stage in their design life. Early in a project it is common to have information from only one or two exploration wells and where water samples are often not available, are heavily contaminated, or have been gathered from locations away from the main production targets.
In the last few years, Shell has implemented three deepwater waterflood systems. They are all on floating installations, employ relatively compact and light weight facility designs and are roughly the same capacity. While their overall designs are similar, important details of the designs are different, and the project management strategies were significantly different as well. The startup and initial run time experience of these waterfloods facilities differed greatly, ranging from significant downtime for the first project to nearly complete success for the last one. Shell is in the process of sanctioning a forth deepwater waterflood system that is larger and more complex than the previous three. Obviously, Shell has already learned a great deal about how to successfully implement a deepwater waterflood project. Before we develop the new project however, we are capturing our waterflood experience to date.
There is limited data on the performance of coatings, materials and cathodic protection systems installed subsea. Most systems remain submerged for their useful life and are often abandoned on the seabed. The recovery of the hardware provided an opportunity to autopsy the hardware for the purposes of validating cathodic protection designs and coating systems; specifically coating performance, anode consumption, and internal wall thickness allowances.