The discovery of the Chinguetti field, nestled in 800 metres of water off Mauritania, called attention to the country as a prime destination for oil and gas explorationists. But the initial skepticism of the size of the Mauritanian play, among earth scientists, especially in major companies, seems to be returning, with the spate of dry holes witnessed in the country in the last one year.
So when the UK operator Dana Petroleum abandoned wildcat Aigrette 1 as an oil discovery in the offshore Block 7 last December, it was a welcome breath of fresh air in an environment that had started becoming suffocated with news of disappointing encounters.
Before this bout of good news, here’s what had happened:
• Dana Petroleum’s Flamant 1, drilled on adjacent block (Block 8) to the one in which the company just discovered some oil, was plugged and abandoned dry, at TD of 3299m in October 2006.
• Woodside’s Cohn 1, in Area A/Block 3, was plugged and abandoned dry at TD of 2,322ms in early August 2006
• Woodside’s Dore 1, located in Area B/ Deep Block 5, was abandoned dry in late January 2006 at 2,266m. These wells are all located in deepwater Senegal basin; they represent the entire deepwater exploration drilling that took place in Mauritania in 2006.
• The only onshore exploratory well drilled was CNPC’s Heron 1, but the Chinese state oil company’s announcement of discovery, at the time that the well had not been concluded, suggests something like clutching to some straw. The well has since been certified unsuccessful.
• Even before the four dry holes in deepwater 2006, Mauritania had set on a dry white season. Woodside’s Zoule-1, in Block 6, was spudded on Christmas day of 2005 and ushered in the 2006 on a cheerless note. At a depth of 3,730m, it was plugged and abandoned (P&A’d) dry.
SO, IT WAS WITH GREAT TREPIDATION that the industry greeted the spudding of the last well of 2006. Aigerette -1 penetrated about 20 m (gross) oil column in the targeted Cretaceous sandstones; the hydrocarbon was identified from pressure testing and fluid sampling. The planned total depth was originally set at 4,925 m, but in order to continue exploration of the Cretaceous section, the well was deepened to a total depth of 5,152 m. Deeper reservoirs in this section, were water wet. The Aigrette Prospect is a low relief, 50-80 m, 4-way dip closure as large as 40 sq km. It was primarily a gas prospect, but was considered to be lower risk than Flamant since it is on trend with the Pelican gas discovery. The primary targets were stacked Cretaceous turbidite sands with some 0.7 Tcf potential. These sands are gas-bearing in Pelican 1. A secondary target was the deeper turbidite sand sequence, not penetrated by Pelican 1. The main risk was the presence of reservoir and structure. The well was spudded on 7 October 2006, at a location approximately 43 km north-northwest of the Pelican 1 gas discovery. The water depth at location is 1.380 m. The results of Aigrette 1 will also influence the view of Block 6 prospectivity.
Two other large structures, considered to have a potential of 100 to 150 MMBOE each, will be drilled in the first quarter of 2007, even while appraisal or a step-out well on the Pelican discovery will be worked on. Early reserves of Pelican are estimated at 1.03 Tcf gas in place and existing 2D and 3D seismic have indicated the extension to the east of channel sand systems which form the Pelican trap. Additional 3D seismic is being planned for this eastern extension.
Another front in the search for the true worth of Mauritania as a hydrocarbon province is the review of the estimated recoverable reserves of the Chingueti field. Operator Woodside has been re-building its structural models of the field and creating a new reservoir model to which the production history can be matched. The results of this work are expected to be made available towards the end of 2006. Woodside has not formally updated its pre-development reserves estimates of 8l MMBO for 1 P reserves and 123 MMBO for P+P, but in August 2006, Hardman Resources Ltd announced that only half of the estimated reserves were expected to be recovered. According to a recent presentation of partner Roc Oil, although some downward revision may occur, the revised STOIIP will be not significantly lower than the original P50 estimate, as the underperformance of the field is believed to be due to the poor reservoir connectivity rather than reduced STOIIP. The problem was identified after a faster-than-expected decline in production from existing wells started in May 2006, and the future of the development plan is being redesigned accordingly. In light of the above a 4D seismic programme will be recorded in early 2007. Recoverable reserves will likely be downgraded, some suggest by up to 25-50% although an official estimate is expected later this year. Partnership includes Woodside Mauritania Pty Ltd (operator), Hardman Petroleum, BG Group plc, Premier Oil plc, Roc Oil and state-owned Société Mauritanienne des Hydrocarbures (SMH). Woodside is now reviewing the candidates for 2007 and 2008 wells, focusing on near Tiof and near Chinguetti potential tie back prospects in Area B, such as Patudo in the Chinguetti concession, at a location 6 km west of the Chinguetti field and Batrachus in the Deep Block 4, 15 km to the southwest of the Tiof discovery. Patudo has a 40 MMbo potential and Batrachus a 35 MMbo potential. The group also plans a series of wells which may include Phase 2 development drilling in the Chinguetti field. Contingent wells include the Awatt and Bogue South prospects in Area A, and appraisal wells on the Labeidna discovery and in the Banda field. The rig, which is capable of drilling in water depths from approximately 100 to 1,500 m, has significant operational flexibility and is able to conduct work on any of the Chinguetti development wells, if ever required, as well as conducting appraisal drilling on existing discoveries.
The Kibaro Prospect is located in Block 4, Area A, about 35 km southeast of the Chinguetti field, in shallow waters. Kibaro is a Cretaceous canyon-confined turbidite sequence that has not been previously tested. The trap consists of two four-way dip- closures within a greater three-way closure which relies on stratigraphic seal along the updip southern canyon margin. The main risks are reservoir presence/effectiveness (net to gross) and trap effectiveness.
