A successful drillstem test offshore southern Tanzania has concluded an intensive appraisal programme by BG Group, which says it can now proceed with plans for a northern production hub utilising three fields with 4 Tcf of gas reserves discovered so far.

The UK major said the test results on the deepwater Pweza gas field in Block 4 confirmed both “the excellent properties of the Tertiary section reservoir, including flow and connectivity, and BG Group’s understanding and modelling of the field’s geology”.

The Pweza field lies approximately 70 km offshore in 1,400 m (4,593 ft) of water. The test on the Pweza-3 well – the first done in Block 4 – flowed at a maximum 57 MMcf/d of gas, and was constrained by equipment. It also demonstrated that development wells could flow at significantly higher rates, and that the Pweza reservoir is potentially the most prolific in BG’s Tanzania portfolio.

According to BG’s block partner Ophir Energy, the appraisal well was drilled approximately 2 km north of the original discovery well and encountered 61 m (200 ft) of gross pay on prognosis. Ophir said the estimated higher unconstrained flow rates could be in excess of 150 MMcf/d.

BG’s chief executive, Chris Finlayson, said: “Our acreage in Block 4 around the Pweza, Chewa and Ngisi discoveries is now fully appraised and tested, with resources in the order of 4 Tcf of natural gas. The work done demonstrates the excellent quality of these fields and that they can be developed as a northern production hub to feed a potential LNG export project.”

The company also added that the well test also confirmed the robustness of its recently announced total gross resource estimate in Tanzania of some 13 Tcf of gas.

The Deepsea Metro-1 drillship is now moving south to Block 1, where it will drill a further appraisal well on the Mzia discovery.

BG is the operator with a 60% interest in Blocks 1, 3 and 4, with Ophir holding the other 40%. The partners are now evaluating 3D seismic survey data to help identify further targets for a new exploration programme next year.
Ophir added that the DST confirmed that the Tertiary reservoirs in Block 4 have “similar excellent characteristics to those in Block 1” and that the result is expected to “dramatically reduce” the number of development wells required in Block 4. This, it says, simplifies the development plan (potentially subsea-to-shore) and has a positive impact on the project’s economics due to the fewer number of wells to drill.

After the Deepsea Metro-1 has drilled the Mzia-3 appraisal, it will move on to drill what Ophir describes as the “high impact” Mlinzi Mbali prospect in Block 7. The Mlinzi Mbali-1 well is expected to spud in the second half of November, and is targeting mean recoverable prospective resources of circa 10 Tcf.

Nick Cooper, Ophir’s CEO, said the Pweza DST completed its near-term appraisal activities in Block 4 and further underpinned these discoveries as a second hub development alongside the Block 1 discoveries.

Offshore