L.C. Jordan (GATE, LLC) | A. Simsek (GATE, LLC) | J.T. Bracey (BHP Billiton Petroleum) | C.L. Bargas (Cobalt International Energy) | F.M. Erdal (Chevron Energy Technology Company)
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. This paper outlines the difficulties faced when evaluating the various scale management techniques available to deepwater operators at the early stages of the project design process and in providing fit for purpose design recommendations that are not overly conservative but that still account for the risk posed by having only limited supporting information available. An approach is presented that addresses these risks and uncertainties by applying scale modeling along with a simple heuristic strategy to support the selection of appropriate scale management techniques for deepwater subsea fields. Several comparative examples for projects in the Gulf of Mexico are provided to explain the different outcomes that can result from this process.
The management of inorganic scale deposition in deepwater environments is often a challenging and costly problem due to the difficulties associated with the treatment and intervention costs when operating remote subsea wells and production systems. This is particularly true for many fields in deepwater basins such as the Gulf of Mexico, Brazil and West Africa, where reservoir pressures can quickly deplete as a result of primary production and drive the use of water injection from early in the field life. The principal water source available to offshore operators during the early stages of production is seawater. Volumes of produced water for reinjection are typically too low to support pressure maintenance during the early to mid-life of many fields and so this can generally only provide a limited fraction of total injection water requirements. Aquifer water injection is also a possibility in locations where a water source is available from zones that are not connected to the primary production horizons. However, the availability of suitable waters in sufficient volumes and at sufficient pressures to justify drilling subsea wells is a rare occurrence. The high sulfate contents available in seawater often drive scale formation following injection water breakthrough at producing wells in situations where mitigating steps are not otherwise taken. The most common scales seen are barium sulfate and strontium sulfate, both of which can be very difficult to remove once they have formed. The difficulties associated with this are often further increased by a lack of available information during the early stages of new-build projects.
Document ID: NACE-11346
Publisher: NACE International
Source: CORROSION 2011, 13-17 March, Houston, Texas
Publication Date: 2011