Hickory, Gulf of Mexico, USA

The Hickory field is operated by Anadarko, which owns a 50% working interest in the Grand Isle blocks 110, 111 and 116, along with partners Shell (37.5%) and Ocean Energy (12.5%).

Hickory lies in the Grand Isle block 116, approximately 75 miles offshore Louisiana in the Gulf of Mexico, in 320ft of water.

DISCOVERY

Hickory is a sub-salt play, in an area where large horizontal salt sheets cover more than half of the Gulf of Mexico's floor. These geological formations distorted the conventional seismic images.

In the initial survey, Raytrace modelling was used to identify seismic amplitude anomalies that can result from overlying salt, so focusing the seismic energy.

The discovery well was made in 1998 by a well drilled using the jackup Global Marine Baltic 1. This well encountered approximately 300ft of hydrocarbon pay in multiple sands. The well was drilled to a total depth of 21,600ft. A 7,3/4-inch production liner was to run the total depth of the well.

DEVELOPMENT

The development/delineation drilling operations were completed in March 2000, when well no 2 was drilled to a total depth of more than 18,000ft. Well no l encountered main field pay zones, downdip of the original discovery well (Grand Isle 116 no 1) located about one mile to the north. Drilled by the Transocean 96 semisubmersible rig, it penetrated a section of salt more than 8,000ft thick - which the company believes is one of the thickest ever drilled in the Gulf of Mexico.

The downhole drilling vibrations caused by the high density of the salt formation meant that Anadarko had to experiment with a number of assembly designs in association with high-torque/low-RPM mud motors, with PDC bits and synthetic muds.

Below the salt is a rubble zone of salt-affected shale, which is characterised by bit-balling and lost-circulation problems. The problem zone usually occurs between 1,000ft and 1,500ft beneath the salt.

In order to reach its target, the second delineation well was drilled as an 's'-shaped hole with a maximum angle of 42°, extending more than 3/4 of a mile from the original well bore.

Anadarko and its partners may drill another even deeper 2,400ft well, in the Grand Isle 116 well, and so potentially extend the lower limits of additional pay intervals encountered by the original Grand Isle 116 well no 1. A separate exploration well has been approved for the Grand Isle block 111 and drilling will begin again, once the work on block 116 is complete.

PLATFORM CONSTRUCTION

The Hickory production platform has been designed to handle 300 million ft³ of gas per day and 15,000 bbl of oil per day, as well as 20,000b/d water. The first production from the Hickory field is scheduled for the fourth quarter of 2000.

The engineering/design services for the project were carried out by Houston-based Paragon Engineering, using PDMS software. The Hickory platform construction was carried out at the Aker Gulf Island Fabrication in Houma, Louisiana.

The three-level Hickory deck weighs 3,500t and is supported by four-legged jackets designed for a 324ft water depth.

One aspect of the projects is that it was designed concurrently with Anadarko's tanzanite platform and the management encouraged a high degree of commonality in terms of equipment used, process configuration, piping and instrumentation/electrical systems applied. It was reasoned that consistent design applications for both facilities would lend flexibility in transferring operations personnel between the two platforms.

Another feature was that both platforms were designed to include programmable logic controllers, rather than pneumatic air systems.

PLATFORM INSTALLATION

The platform will be installed either by Heerema’s heavy-lift barge SSCV Balder or by the SSCV Hermod.