Abstract

New seismic mapping revealed a Lower Miocene reefal buildup on a separate fault block west of the South Lho Sukon (SLS) "A" gas field. The seismic shows a mounded feature with bifurcating double-legged strong amplitude reflectors, presumably the top and bottom of the reef, and high interval velocity. This seismic anomaly was noted in old vintages of seismic lines, but it did not become clear as a possible reef until the new 3D seismic was studied in 1989.

The basement fault which separates the D1 discovery from the SLS "A" structure is believed to have moved as early as the Late Oligocene, and it continued into the Miocene as attested by the increasing throw with depth. The early existence of the basement horst was essential for the Early Miocene reef growth.

The D1 well penetrated 943 feet of reefal limestones at the Peutu level. The limestones consist of mudstones, grainstones and some boundstones. Log analysis indicated 920 feet of net pay with 12% average porosity and 14% average water saturation.

The new field probably will be developed jointly with the neighboring "A" field of similar size. The new discovery definitely has upgraded the future potential of the South Lho Sukon and Pase areas. New seismic surveys in the areas are being conducted in hope of delineating more prospects.