Expansion of subsea technology usage (Image courtesy of Quest Offshore)

Subsea technology has evolved and matured, with around 5,000 subsea wells worldwide, and today it is being used by a much wider group of companies exploring and operating subsea assets.

Subsea technology has also developed in complexity at a quick pace, providing today a much larger suite of options to choose from. Longer tiebacks and deeper water are pushing the technology across all the disciplines. Fast-track projects require rapid and well-informed decision-making.

To tackle the complexity and the innumerable combinations of subsea technological solutions, only employing an integrated engineering approach will allow the full impact of each of the solutions proposed to be understood and enable the most feasible solution to be optimized.

An integrated approach should include a rigorous process for identifying all the feasible alternatives, analyzing the positive and negative impacts of such solutions and ranking the solutions based on the value drivers for that particular project. Those value drivers may differ substantially from one field to another, as demonstrated by the following examples:

Total hydrocarbon recovery. It has been well publicized that operators have an incentive to enhance the recovery factor of their fields and extend the useful life of assets in place.

Local content. With partnerships with local governments, operators may be required to commit a certain percentage of the total project capital to local goods and services.
First oil/first gas. Beyond the obvious cash flow and present value incentive to anticipate production of fields, some projects have sale contracts in place in advance of the construction, and missing the delivery dates may have associated severe penalties.

Technical risk. After so many years and so many innovations in the subsea arena, operators still have significantly different appetites for technical innovation and associated technical risks. As an example of this, today after many decades and several hundred million dollars invested, there is only one operator with a subsea separation facility in operation.

It is important that certain key interfaces and tradeoffs are identified and addressed in the screening and selection process. This should not be taken as a shortcut to fully integrated analysis but rather as a method to simplify the problem and accelerate the engineering phase.

Here are some typical examples of key areas to be addressed in any integrated engineering study:

Riser x Hull selection process. In order to optimize the solution, it is important that the operator identifies the mutual impact of riser systems and hull designs in the early concept selection process. With the abundant alternatives for hull shapes and riser systems, the process should focus on the elements with the largest cost and schedule impact to the development, eliminating the technical solutions that are not feasible or do not fit the risk profile for that particular operator.

Figure 1 provides a quick summary of the typical screening tool for hull selection. This tool has been used for assisting operators to narrow the number of alternatives to be studied in more detail during later phases of the project. MCS has used such a tool in several deepwater projects such as Chevron’s Nsiko in Nigeria, where the impact of different riser designs to the hull were critical to establish the feasibility of different field layouts.

Field layout x flow assurance. Drill center locations impact not only the drilling and completion programs for the subsea wells, but also the subsea field layout, in turn, directly affects the pipeline routes and consequently the flow assurance and operability of the field. Operators should emphasize the need for multidisciplinary teams that can identify the optimization opportunities.

In shallowwater tiebacks it is important to rationalize the pipeline size in order to reduce overall material costs. Flow assurance studies determine the pipeline size, but where there is an elevated level of uncertainty — as is the case in early conceptual studies — only by engaging in a systematic review of the operational transient conditions, expected flow rates, topography and topside facilities can the pipeline size be properly evaluated.

MCS recently completed a conceptual study where different pipeline sizes were evaluated using a wide range of operational conditions. The most appropriate pipeline size would have to deliver the maximum rates without imposing excessive velocities, and the minimum rates without excessive liquid holdups. Our recommended solution was reached only after a complete transient analysis had been performed, and the outcome was somewhat of a surprise to the operator since a previous steady-state study selected a larger pipeline size for similar operational conditions.

Material selection x constructability review. Hydrocarbon fluid composition and flowing conditions can be challenging to typical carbon steels, and exotic alloys may have to be selected.

Different martensitic stainless steel materials are available today, presenting more flexible options for construction of subsea pipelines and reducing post-weld heat treatment requirements. Not only is the metallic materials universe expanded, but the use of nonmetallic materials is also increasing. These materials are replacing steel in many subsea applications.

Availability of such materials in remote locations and proper training and experience of local workforce with such exotic materials may pose an additional construction risk to the project. There are several examples of projects that have selected a particular design for a steel structure based on the experience of the engineering staff. However, when such design was reviewed by the local fabrication yard, several modifications to the design were required to conform to the local capabilities.

Innovation x reliability. Some operators consider innovation as the equivalent of adding risks and reducing reliability of subsea systems and therefore its availability. Innovative solutions may bring to the fore field-proven technology but with a novel approach. Electrical submersible pump technology is an example of a field-proven solution that has been recently repackaged for seabed pumping applications. Similarly, coiled tubing has been gaining credibility as a viable solution for pipelines of small diameter.

It is important to analyze the potential benefits of new technologies in engineering studies, taking into consideration that such technology may mature within the project timescale. Ruling out technological advancements from feasible alternatives may impose unnecessary economic penalties to such developments. Examples abound of technical solutions that have provided windfall profits to the operators that have taken the “additional risk.”

In our past experience, the following are critical areas of interest for the operator in such engineering studies:

Independent review. With so many proprietary concepts in riser and hull technology, the operator needs to be provided an impartial and unbiased review of the alternatives.

Installation and constructability review. Many projects have incurred additional costs and schedule overruns recently, and operators’ concerns revolve around the suitability of the designs to the specific challenges of the project.

Operability review. Many subsea components are critical elements in enhancing or warranting the delivery of the expected production; therefore, such elements should be reviewed in the light of operational requirements and its impact on such requirements.