DRILLING & PRODUCTION

John Waggoner • Houston

VAALCO drilling off to strong start in Gabon

VAALCO Energy has drilled one pilot hole south of the original Ebouri discovery and a second pilot hole northeast of the original discovery offshore Gabon. The holes delineated additional Gamba sandstone reservoir above the oil/water contact, thereby increasing the acreage and reserves of the Ebouri field. VAALCO is completing the development well horizontally on the same orientation as the second pilot hole. First oil production from the well was expected (at presstime), the company says.

The company also hit with the North Ebouri appraisal well in the Etame block northeast of the Ebouri platform. The well struck a 21-ft (6.4-m) oil column, further expanding Ebouri field. VAALCO plans a sidetrack to optimize the location for a possible second horizontal development well. In addition, the company plans two exploration wells (North Etame and South East Etame) on newly mapped structures. The wells will be drilled back-to-back usingPride Cabinda.

VAALCO expects to bring total production from the Etame license to approximately 25,000 b/d of oil. The Etame license areas currently produce approximately 20,000 b/d, of which VAALCO has a 28.1% working interest.

The piling operations were performed on schedule and without incident exactly as planned, despite the soil variety. The $2-million drilling and grouting contract was the first ever for newly formed Large Diameter Drilling (LDD) Ltd.

Since the project is based on a floating construction vessel, heave forces were the main concern. The motion of the vessel could damage the well or the equipment, causing project delays.

Given the mere 1.5-in. (3.8-cm) radial tolerance from the bit through the center of the 42-in. (107-cm) tubular pile, LDD opted to use a passive heave compensator to keep the drill from snagging on withdrawal or from touching the base of the pile.

The heave compensator, with a 3-m (10-ft) stroke for safe working loads up to 60 tons (54 metric tons), was able to reduce point loading to just under a ton (907 kg).

“As far as we are aware, no one else has ever used a lift compensator such as this for a drilling and piling operation,” says Andy Seager, operations manager at LDD.

Soil conditions posed an unexpected twist when high concentrations of clay were encountered. Two years previously VAALCO installed the Avouma platform, and given the similar geology, opted to forego additional site investigation.

Once drilling began, clay appeared. At times it was unconsolidated and inter-banded with weak layers of mudstone, siltstone, and sandstone. Since the hard mudstone and sandstone sub-base of the formation ruled out a driven pile solution, the choice of raked piles tended to aggravate the problem.

Once the socket was completed and before the drill bit and bottomhole assembly were removed, the hole was backfilled with a proprietary shaft-stabilization mud to support the unconsolidated clays and weak layers. This increased the socket stand-up time for safe pile insertion and grouting.

AnTech wellhead outlet stays cool in HP/HT wells

AnTech has re-engineered its wellhead outlet to operate safely in the higher temperatures generated by high-pressure/high-temperature wells. The outlet responds to customer demand for an ATEX-certified tool that could be operated safely in today’s hotter wells, the company says.

“With the dramatic rise in the number of HP/HT wells, it was time to take the tool to the next level,” says Toni Miszewski, MD of AnTech.