Chasing a New Carbonate Fracture Play Type at South Sumatra Basin

Abstract

The newly discovered giant basement fracture gas reservoir in Sakakemang block located in the central part of North Palembang Sub-Basin has been an interesting subject and brings a new perspective in exploration on that basin. However, due to the lack of recent exploration activity, the southern part of this basin, the hydrocarbon potentiality is less known although the remaining potential remains high. This paper will discuss the hydrocarbon potential of the basement fractured in an area located in the southern part of the North Palembang sub-basin, 100 km to the southeast of Sakakemang block.

The geological delineation from Kaliberau discovery trend can be continued, about 100 km to the southeast, called the “X” Structure. The evidence from the well, seismic, and gravity data are integrated to construct the geological model. The previous operator has made a gas discovery from the shallow gas reservoir of Telisa. However, the current operator sees there is a new potential basement fracture at the deeper level.

The “X-1” well drilled 75 m of recrystallized carbonate. While drilling the carbonate, the previous operator experienced a partial loss and the petrophysical analysis reveals the development of secondary porosity. The total gas reading also increased, even higher than the current pay zone at Telisa sand. The seismic facies are showing a widespread carbonate platform, with “X-1” well at the crest of the structure. The thickness of the carbonate can reach >250 m.

The seismic evidence is showing a large (5x10 km), inverted structure from the seismic. This is also supported by the geochemistry and basin modeling evidence. The basin modeling records that there were at least 2 inversion timing, which are Middle Miocene and Plio-Pleistocene. The erosion calculation from basin modeling is showing more than 1000 m sediment has been eroded at the “X” structure. The petrography analysis is showing a feature of type III/IV twinning-calcite, indicating a hot paleotemperature, with intensive icrofracture. This inversion history is very important to facilitate the fracture porosity in the basement.

The “X” carbonate reservoir represents a buried carbonate which inverted massively. Without the fracture, there is no chance for this reservoir to develop a matrix porosity. Adjacent to 2 km, the kitchen is able to produce gas. Within the fracture and permeable sand, the gas should be able to reach carbonate. In South Sumatra Basin, there is no current analog that has been discovered in this play type. The discovery of carbonate play type will bring a new play concept
into South Sumatra Basin.