Location and Ownership

The Llano field is located in the Gulf of Mexico, spanning Garden Banks blocks 385 and 386, approximately 200 miles southwest of New Orleans in water depths of around 2,600 feet. Shell operates the field with a 27.5% interest, alongside Amerada Hess (50%) and ExxonMobil (22.5%). In May 2002, Shell Exploration & Production Company (SEPCo) acquired Enterprise Oil, securing the lease for GB 385 and 386.

Reservoir Details

The Llano reservoir is situated in turbidite sands at depths of approximately 24,000 feet subsea in the Pliocene layer and 26,000 feet subsea in the Miocene layer. It features two zones with net thicknesses averaging 150 feet in the Pliocene and 95 feet in the Miocene. The reserves consist of both oil and gas, with an API gravity of 28° and sulfur content of about 1%. The total gross ultimate recovery for Llano’s initial development phase is estimated at 40 million barrels of oil equivalent.

Discovery Well

The Llano discovery well was drilled to a measured depth of approximately 27,800 feet in 1998, following two sidetracks using the Transocean Voyager and Omega. The field began production from one well, producing 10,500 barrels of oil and 26 million cubic feet of gas per day. A second well commenced production at the end of May 2004.

Development and Tieback

Shell has developed Llano using a subsea system tied back 11.5 miles to its Auger Tension Leg Platform (TLP) on Garden Banks Block 426 in 2,860 feet of water. The expandable subsea system initially consists of two wells tied back to Auger via a pipe-in-pipe looped flow line. Llano is SEPCo’s second project to use 15,000 psi subsea equipment.

Pipelines and Flowlines

The Llano pipeline network includes two pipe-in-pipe (PIP) flowlines and a single infield PIP flowline, comprising:

1. An 8.625-inch-diameter, 1.158-inch wall thickness API 5L X70 SMLS carrier pipe surrounded by a 12.75-inch-diameter, 0.5-inch-thick API 5L X52 HFIW casing pipe.

2. The 8.625-inch carrier pipe insulated with a 1.3-inch-thick jacketed polyurethane foam.

The flowline system includes three PIP flowline initiation sleds located in 2,500 to 2,620 feet of water using pre-installed suction piles. The installation also includes an infield PIP flowline termination sled and two 6.625-inch-diameter, 1.067-inch-thick API 5L X70 SMLS steel catenary risers (SCRs) insulated with 3.5 inches of Glass Syntactic Polyurethane (GSPU) insulation.

Engineering and Installation

All installation engineering was performed by J Ray McDermott Engineering. Specialized procedures and tooling allowed the outer casing pipe to slide unimpeded over the inner casing pipe during offshore welding and installation. Water stop seals and other procedures were used to prevent moisture entry into the PIP flowline annulus during installation.

An SCR installation mast was designed for transferring SCRs between the DB50 and the Auger TLP. All flowline installation activities were carried out by the Derrick Barge No. 50 (DB50) using J-Lay methods, with welding performed by the JRM Vermatt Bug-N-Band Automatic Welding System (JBBS).

Production and Capacity

The Auger TLP has dedicated production capacity for 25,000 barrels of oil and 75 million cubic feet of gas per day, with peak production expected to reach 32,000 barrels of oil per day. Total development costs are approximately $215 million, including modifications to the Auger TLP.

Contractors

J Ray McDermott handled detailed engineering, subsea, pipeline, and marine installation. Other major contractors included:

1. FMC

2. V&M

3. Simrad

4. Sea Cat

5. Tenaris

Bayou Pipe Coating managed joint fabrication, Shaw Pipeline Services conducted inspections, Fugro Chance provided surface and acoustic positioning, and Oceaneering delivered ROV services. Porter Services fabricated the PL sleds.