New drilling barges, liftboats to rehabilitate Lake Maracaibo fields

Prisa vessels slated for workover, horizontal work

William Furlow
Technology Editor
Petroleos de Venezuela (PDVSA) has commissioned the construction of three new generation multiservice drilling barges and three powered liftboats to head up new drilling operations and a workover program on fields in Lake Maracaibo.

The Prisa project consists of a 10-year contract between state oil giant PDVSA and Schlumberger. The vessels will be built and owned by Schlumberger's Sedco Forex division and will integrate Schlumberger services into their design. Prisa, the name given to this overall project, is a Spanish verb meaning "to do things quickly." It is also an acronym in Spanish for Perforation, Rehabilitation, Integration with Services in Alliances. In this context the name translates to the duties the barges will perform.

Constructed by Semco of Lafitte, Louisiana (US), the first of three Prisa liftboats will depart the yard later this month. The boats will be used for coiled tubing re-entry work and under balanced drilling to enhance production from existing fields. TDI Halter is also constructing three multi-service drilling barges to perform new drilling operations on the lake.

Prisa 101, 102, 103

The Prisa multi-service drilling barges, named Prisa 101, 102, and 103, are designed to perform horizontal drilling operations, underbalanced, multilateral and short radius drilling, horizontal reentry, wireline logging and perforating, measurement while drilling (MWD), logging while drilling (LWD), gravel packing, cement pumping, and completion work.

The vessels feature an integrated cantilever derrick and major support facilities including a mooring system, crane, power generation, and fluid and pumping and storage equipment.

The vessel's modular design allows for quick upgrades and modifications. It includes custom iz ed equipment that will be used for slimhole, short radius, and multilateral drilling. A central control cabin can monitor all derrick, drill floor and slickline operations.

The first of these vessels currently is enroute to the lake, and the second is scheduled for delivery later this month. The third should be complete by year's end. The design of these vessels reflects the nature of Schlumberger's contract with PDVSA on this job. The 10-year payout contract is virtually a turnkey deal.

Schlumberger has integrated its wireline and measurement equipment into the vessel so there will not be the traditional free-standing Schlumberger shed. Instead, these systems are controlled and monitored from the crew facilities on board the rig. This integration means all major operations can be controlled from a centrally located series of offices.

This improves communication interaction between different operations on the rig. The vessels have crew quarters and facilities to handle a complement of 44. Traditionally, a Lake Maracaibo crew works a single shift, then catches a boat to shore between shifts. Schlumberger will work its crews on the conventional offshore shift of two weeks on-two weeks off. There are substantial time savings involved in eliminating all these boat rides in addition to the reliability of knowing the crew members will be on the vessel when their shift starts.

Greater automation

The rig floor of the vessels will be automated to the greatest extent possible for Lake Maracaibo operations. The vessels are designed to work in 80-100 ft water depth, with wells drilled to 7,000 ft, with minimum preparation for weather changes, which are abrupt in Lake Maracaibo.

To shorten the critical path, the vessels feature a dual derrick system with a second mouse hole, so pipe can be made up or broken out without affecting drilling or tripping out of the hole. Because the wells are drilled in shallow water and to a relatively shallow horizon, the decision was made to use double stands of pipe rather than the industry standard triples or deepwater quads.

By running doubles, the barges are operating with a lower derrick profile, allowing them to continue operations in inclement weather. This ability to operate through most storms rather than shutting down, combined with the dual activity system, should more than offset the extra trip time needed to run doubles instead of triples.

The vessels feature automated tongs that spin and break out the drill pipe using hydraulic power, but does not feature the latest automated pipe handling equipment. Again, the thinking is that the added benefits of high-end automated equipment can only be offset in deepwater wells where trip times are great enough to produce a major benefit from such automation. The barges use a hydraulic top drive and are also equipped with a traditional kelly drive. In the event of a top drive failure, the kelly ensures drilling can continue.

The vessels will not be outfitted for coiled tubing work initially, but the first barge being sent to the lake will be loaded with the necessary equipment to upgrade for such an operation.

Another efficiency built into this project is the interchangeability of the three barges. A single parts list will be maintained onshore, and the equipment such as coiled tubing and underbalanced systems can be used on any and all of the vessels. One set of specifications is much easier to maintain nearby than three separate lists.

The drill floor control room is equipped with three independent monitoring systems so the operator can keep track of three different data streams at once. For example, the operator can monitor the well control system, strip charts, and manual board readings simultaneously.

The barges will work initially on three named fields on the lake: La Salina, Lagunillas, and Bachaquero. All three fields are well established producers on the east side of the lake. Because of the design limitations of the barges, they will not be working in the southern regions of the lake, where water depths exceed the 80-100 ft limits of the barges.

Prisa 110, 111, 112

The multi-purpose service vessels (MPSV) are being custom built to perform shallow water intervention services on wells in Lake Maracaibo. They feature bow and stern thrusters for quick mobility and precise positioning. They are designed to operate in up to 100 ft of water, and can perform light, medium and heavy well intervention work.

The MPSVs are equipped with the latest drilling and data management technology. They are capable of complete coiled tubing running, drilling and workover operations, horizontal reentry, underbalanced workovers, under balanced coiled tubing work, pumping and well treatment services for workovers, gravel packing, cement pumping and MWD, LWD, and wireline logging and perforating services.

Because these vessels offer such a wide range of services they give operators an economic alternative to purchasing these services piecemeal. The Prisa MPSVs also reduce the time it takes to complete workover operations and offer a flexible package of diverse service options.

The new vessels are based on the Power Offshore P170 design, and make use of a number of Sedco Forex innovations. Among these are the integrated cantilever derrick, mooring system, power generation and fluid pumping and storage equipment.

Copyright 1998 Oil & Gas Journal. All Rights Reserved.

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