| Popis: |
A field in the Central North Sea produces oil from a Forties type reservoir with seawater pressure support. The high salinity formation water contains up to 450mg/l barium, creating a significant scaling risk to the wells, all of which now show seawater breakthrough. The operator was required to replace a scale squeeze inhibitor carrying a substitution warning, and the need for a more cost effective squeeze lifetime was also a driver for change in a field containing complex wells with highly variable permeability, and a challenging placement environment. Evolving environmental legislation in the North Sea has forced changes in the type of scale inhibitor which may be deployed in the UK and Norwegian continental shelf. Phosphonate scale inhibitors have been on the substitution list or phased out for some years, leading to a technology gap for scale squeeze applications, where polymer inhibitors often show relatively poor squeeze lifetimes or can be difficult to detect readily at residual concentrations compared to phosphonates. This paper presents the laboratory evaluation and field application to several wells of the new scale inhibitor, describes the application of the scale inhibitor in complex wells using a combination of placement techniques such as crossflow balancing during shut in and diversion using wax, illustrates that the new inhibitor has demonstrated improved retention and desorption characteristics leading to longer squeeze lifetimes while highlighting the disadvantages of relying on wellhead scale inhibitor analysis alone for scale management of heterogeneous wells. This paper will illustrate the possibility to replace traditional phosphonate scale inhibitors which carry a substitution warning with a chemical which shows much improved squeeze lifetimes over traditional polymer alternatives, leading to a reduction in campaign frequency and resultant cost savings. The lesson learned from these applications can be shared with other subsea producing basins such as those found in offshore Gulf of Mexico, Brazil and West Africa. |
