Abstract: Stratigraphic and Depositional Analysis of the Regressive Gumai Sands of the North Geragai Field, South Sumatra

DESAUTELS, DAVID; PETER M. LLOYD

The North Garagai field was discovered by Santa Fe E. R. Jabung in 1995 in the South Sumatra Basin. The discovery well was drilled on a seismic high. Subsequent appraisal drilling has resulted in the further integration of high resolution image, dipmeter, open hole logs, core and cuttings data to develop a depositional model.

The reservoir zone comprises a 1500 ft thick Upper Gumai deltaic sand shale sequence which prograded out to the west from the Sunda Shelf during the mid Miocene.

The open hole log and FMS^TM data were used to describe the subsurface facies and hence interpret the depositional setting of twenty correlatable sands developed across the structure. Lithology, sedimentary structures, paleocurrent direction and sand body geometry and orientation were determined by careful integration of the data using an interactive computer workstation. Characteristics of the four main reservoir sand types - distributary front, tidally reworked shelfal, distributary channel and point bar - are described in detail.

The North Garagai discovery and initial appraisal wells were drilled in the more distal parts of the prograding deltaic sequence. Understanding the main lithotypes and paleocurrent directions has enabled thicker and higher reservoir quality sands to be penetrated in the more proximal parts of the deltaic sequence during appraisal drilling. Reservoir mapping and property prediction were constrained (where possible) by using predictive interpolation between the wells based on the depositional models.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria