Abstract

Mobil Oil Indonesia has completed drilling seven new horizontal development wells and recompleted two previously drilled wells to produce gas from the SLS-A and SLS-D Miocene reef fields onshore B Block North Sumatra. In addition, two field extension wildcats were drilled adding knowledge about the reefs' growth history and gas accumulation. The producing wells (8" in diameter) have 500 meter horizontal sections and produce at prolific rates of more than 60 MMCFPD each from Miocene patch reef complexes, supplying 520 MMCFPD for processing into LNG at the Arun Plant.

The development wells have revealed several surprises worth reporting. The original geologic model was one of relatively homogeneous reefal carbonates caused by pervasive secondary diagenesis with a general trend toward lower poroperm at the base. Instead, core and production testing reveals that permeability may have substantial lateral variation indicating preservation of the original reef fabrics. Tests indicate that the adjacent platform facies may be pressure separated from the main reefal body. An extensive cave collapse system is interpreted near the crest of the reefs on 3D seismic where wells have penetrated shale bodies within the reef. These cause numerous flow boundaries on well tests.

This paper will report on the new integrated geologic model and its effects on production characteristics.