Oman: Neoproterozoic limestone yields oils

By OGJ editors
HOUSTON, Jan. 18
-- Test results from the Saiwan East-4 well on Block 4 in eastern Oman suggest the oil in this part of the block is of different quality from the oil encountered in previous Saiwan wells, said participant Tethys Oil AB, Stockholm.

CC Energy Development SAL, operator with 50% interest, drilled SE-4 in mid-2010 but did not test it at the time. Well data also suggest considerably larger parts than previously believed of the more than 400-m thick Neoproterizoic Khufai limestone section could contain oil of various qualities, Tethys Oil said.

The oil encountered in SE-4 could range in density from the 33° gravity oil produced from SE-2 and SE-3 to the heavy oil encountered above the Khufai in these wells.

In the previous Saiwan SE-2 and SE-3 wells, oil was only confirmed in the upper parts of the Khufai section. The extensive log and core data obtained from SE-4 in mid-2010 has now been expanded by data from six production tests spanning more than 400 m of separate intervals principally in the Khufai limestone.

No flows were established, and some hole conditions resulted in encountering water- bearing fractures in the top part of the Khufai, interfering with test data from this zone. The actual production capability of SE-4 therefore remains undetermined, Tethys Oil said.

The SE-4 results will prompt reevaluation of the data obtained from SE-2 and SE-3 as regards the potential for oil also in the lower parts of these wells. Further analysis will be done in SE-4, and the well will remain suspended to allow for more production tests later.

Immediate focus will be to drill the next Saiwan well. SE-6 is being drilled 2.4 km north of SE-3 to appraise the northern part of the Saiwan area.

Tethys Oil said, “The Saiwan area continues to surprise us. Last summer we encountered way better flow rates than expected in SE-3 when this well flowed more than 10,000 b/d of 33° gravity oil from the upper parts of the Khufai. In SE-4 we seem to have encountered unexpectedly large quantities of oil with different gravities and viscosities than previously believed possible.

“We will have to wait and see what impact this will have on the resource calculation, but indications are that yet a new play concept may have opened up. The results underscore the complexity, but also the potential, of Block 4 in general and the Saiwan area in particular.”

Tethys Oil has 30% interest in Blocks 3 and 4, and Mitsui E&P Middle East BV has 20%.

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