A 2100-foot, 14-inch steam line was installed under a ship channel to provide steam to wells on an island location. Designed to operate at 600 F and 1600 PSIG, the line transports wet steam (80% quality) for steamflood injection. The insulated line was installed inside of two concentric casings to allow for 8 feet of thermal expansion and to facilitate installation. Although the design had to overcome uncommon problems, the solutions were based upon using common methods and materials.
Tidelands Oil Production Company operates a steamflood project in the Tar Zone of Fault Block II-A in the Wilmington oil field, Los Angeles County, California (Fig. 1). The steamflood reserves are located within the Ports of Los Angeles and Long Beach and extend from the coastal mainland to Terminal Island.
Expansion of steamflood operations required extension of the main 14-inch steam transmission line across a ship channel to Terminal Island (Fig. 2). Steam is supplied from Harbor Cogeneration Plant on the mainland, so the source could not be relocated.
The channel crossing was accomplished using conventional directional drilling for pipeline installation to install a 30-inch welded steel casing. This provided a near-linear alignment and allowed the steam line to grow 8 feet longitudinally without overstress. The steam line was anchored to the end of the casing, and the casing was anchored naturally by the surrounding soil.
A 24-inch welded steel inner casing was slid over the insulated 14-inch steam line to form a single 2100-foot string, and the dual concentric string was pulled through the 30-inch casing. The inner casing provided secondary protection from groundwater and simplified the installation of the steam line under the channel.
The soil over the pipeline provided a thermal insulating layer up to 130 feet thick, which caused the casing and surrounding ground temperature to exceed 300 F. The high temperature raised issues regarding casing integrity and coating. The inaccessibility of supports and guides presented problems with assuring support integrity during installation and operation.
The final installation avoided the use of components which would fail under localized heating up to 600 F, and relied on a conservative design and the redundancy of an inner casing. The casings are uncoated, but cathodically protected to reduce corrosion. The steam line supports, clamped over ceramic spacers, were designed for steel on steel sliding surfaces. The anchor design is simple, using standard flange bolting and insulating material, but can accommodate much more than the anticipated loads. Expansion at the free end of the steam line is accommodated by piping flexibility with a single loop.
Type of Crossing. The casing for the steam line was installed by conventional directional drilling for pipeline installation, to a maximum depth of 150 feet below sea level. The crossing consisted of sloped straight segments on each side and a long arc (2500-foot radius) near the center. There are no bends in the casing and steam line from one side to the other, other than this long deflection. In heating up from 60 F to 600 F, the steam line freely expands 8 feet longitudinally in its 2100-foot crossing length. It is not possible to fully restrain the line during heat-up without exceeding the allowable stress limits, so the steam line was installed within a welded steel casing and is free to grow.
Initial analysis considered a single 30-inch diameter casing. The design evolved to include a 24-inch diameter inner casing and a 30-inch outer casing.
Steam Hydraulics. A simulation of the two phase steam flow was performed to assess slugging and liquid holdup in the channel crossing. The projected flow rate to the first two wells to be drilled on Terminal Island is 50,000 lb/hr, equivalent to 3,000 barrels per day of water. Liquid holdup is low in the downward sloping section, varying from 2% to 9%. Liquid holdup is higher in the upward sloping section, varying from 28% at lower flow rates to 9% at the full output of the cogeneration plant, 465,000 lb/hr. Slugging is not a problem, however, because the slug volumes are relatively small and the velocity is relatively low.