Two downhole pressure-monitoring campaigns in 2000 and 2001 proved that long-term memory gauges can function properly, withstanding high temperatures and pressures for more than 100 days.

Neil Ferguson is technical coordinator of Cased Hole Services for Expro Group Algeria.

In early February 2000, Expro Group Algeria was invited to tender for pre-startup reservoir interference testing work on the Ourhoud field reservoir, situated 217 miles (350 km) southeast of Hassi Messaoud in the Algerian Saharan Desert. The operator is an entity known as the Ourhoud Organization, comprising Sonatrach and partners CEPSA, Anadarko, Burlington, Maersk, Lasmo and Talisman.

The Ourhoud Field is scheduled to begin producing 230,000 b/d of oil from the Tagi reservoir in 2003. The field development plan filed by the unit partners proposed reservoir pressure support by peripheral water injection and crestal gas injection. The objective of the work was to investigate, by a series of pre-startup reservoir interference tests, the effect of compartmentalization on these planned pressure support schemes.

Ourhoud Organization recognized that it would be necessary to utilize long-term memory gauges to survey conditions within the injector wells and observation wells in the field.

Reservoir conditions were specified as 220°F (104°C) with a bottomhole pressure (BHP) of 7,500 psi in the injector wells and 5,200 psi in the observation wells. The team deployed three gauges per observation well downhole for a maximum survey duration of 90 days, and two gauges into each injector well for a maximum survey duration of 180 days. The successful outcome of the job was contingent on two out of three gauges in the observation wells and one out of two gauges in the injector wells recording 100% of the data. Any gauge out of specification upon retrieval - despite recording data - was deemed to have failed.

Equipment selection

Expro's Algerian project team formed a liaison with technology support teams in Aberdeen and Great Yarmouth, United Kingdom, to leverage experience and propose a suitable project plan.
The team provided tool strings comprising 400SQ Memory Gauges (see Figure 1), which have a proven track record. In total, 26 gauges complete with long-term housings and crossovers were required, along with eight heavy-duty shock absorbers, eight knuckle joints and eight heavy-duty centralizers.
To ensure efficient operations and services on site, the team established a maintenance and verification facility in Hassi Messaoud. Expro offered regular preventative maintenance visits by a senior technician specializing in cased-hole services.

Year 2000 campaign

Ourhoud Organization awarded Expro Group Algeria the long-term memory gauge contract in May 2000. Crews mobilized the equipment in June 2000 and ran the first gauges downhole in July.
In total, the team carried out 13 surveys in the campaign, resurveying some wells because of compartmentalization within the reservoir. The final gauge set was pulled out of the hole in May 2001.
The number of downhole gauge days in the campaign amounted to 3,566 days with an average survey duration of about 100 days. The gauge success rate for the campaign was 100%.

As part of the 3,566 gauge days, the team ran two short Solo gauges downhole on a well where the preferred toolstring could not be used because of the well control rig-up. Both Solo gauges were downhole for 62 days with standard battery packs and recorded 100% data as programmed.

Year 2001 campaign

Due to the success of the 2000 campaign, Ourhoud Organization awarded further memory gauge work to Expro in 2001, this time with 21 additional wells in the program.

Using the same technology, the team ran the first gauge set downhole in May 2001. The final gauge set was pulled out of the hole in January 2002. The number of downhole gauge days in the 2001 campaign totaled 7,167 days with an average survey duration of about 110 days. The gauge success rate for the campaign was 95%.

Success breeds success

Since gaining a reputation in the region for the Ourhoud Organization work, Expro has performed additional gauge surveys, memory production logging and bottomhole sampling work. Burlington Resources, a member of the Ourhoud joint venture, contracted Expro Group to perform a 10-well, 150-day, long-term survey on a separate prospect, and this campaign was completed in April 2002.

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