The Enrekang Sub-Basin Investigation was conducted as the northern part of the Sengkang Basin. Tectonically, this area is included in the western mandala. According to Coffield (1993), South Sulawesi is divided into the Latimojong Formation as bedrock (pre-rift sequence), the Toraja Formation (syn-rift sequence), the Enrekang volcanic series (syn magmatic), and the Walanae Formation of the Tacipi Member (syn orogenic).

From the results of the study, the location of data collect for the Enrekang Sub-Basin were divided into 4 regions, namely Kalumpang, Rantepao, Toraja and Enrekang. The rocks in Kalumpang are dominated by mud flat deposits and a small portion of mixed flat, channel and sand flat deposits. There are also several coal seams in this area. The facies rocks at Rantepao are more dominated by repeated mixed flats, sand flats and mud flats. It generally consists of sandstone, siltstone and claystone which are thinly layered. The rocks from Toraja to Enrekang are shelf deposits in the form of carbonate claystone, dominant in younger deposits and overlapping sandstone facies. The rocks of this location are included in the Toraja Formation and the Makale Formation. The Makale Formation is dominated by packestone-grainstone limestone, relatively turbid, possibly deposited in a backreef environment. The distribution of the Toraja Formation has a southwestern-northeast direction, while the difference in trend patterns is caused by tectonic compression forces.Changes in the depositional environment have a northwest-southeast distribution direction, namely proximal deposits in the northwest (Kalumpang, Mamuju Regency, West Sulawesi Province) and distal deposits in the southeast (Enrekang Regency, South Sulawesi Province).From the observation of thin sections it is known that the rocks in the study area are dominated by limestone, including packstone, wackestone, grainstone and boundstone, and a small portion is arkose arenite.The rocks in the study area were formed from the Eocene to the Miocene with the presence of the Nummulites and Lepidocyclina families. Based on Wilson (1975), the rocks in the study area are formed in the environment of organic build up facies belts, winnowed edge sands and open circulation shelf lagoons.From the analysis of gravity of the Enrekang Sub-Basin, it can be seen that the shape of the Paleogene basin has a long direction northwest-southeast and a wide direction southwest-northeast. This shows that the distribution of the Toraja Formation has a relatively southwest-northeast trend.Seismic analysis has been carried out with the total seismic lines are 247 lines consisting of 3 vintanges, 17 wells used, namely: 1) BBA-1X; 2) Bonge-1; 3) Gilirang A-1x; 4) Kampung Baru North-1, 5) Kampung Baru-1; 6) Kampung Baru-2; 7) Kampung Baru-3; 8) Kampung Baru-4; 9) Kampung Baru-5; 10) Kampung Baru-6; 11) Lamata-1s; 12) Peniki-1; 13) Sallo Bullo-1s; 14) Sampi – Sampi-1; 15) Tironge-1; 16) Walanga-1; and 17) Walanga-2.

Based on the results of field investigation, the carbon-rich mudflat deposits from the Toraja Formation have the potential to be hydrocarbon source rocks (confirmed by macro seepage test results). Potential as reservoir rocks are sandflat deposits from the Toraja Formation, the clastic limestones of the Makale Formation. Meanwhile, the marine claystone of the Toraja Formation and limestone of the Makale Formation have the potential to be used as cap rock.From the results of research and interpretation, it can be seen that the concept of each well and the seismic data around it is different and highly dependent on the pattern of geological structure and the developing petroleum system. The concept model in western South Sulawesi shows that most of the accumulation will be driven by the existence of a fault structure pattern. This fault-shearing anticline ridge is a pretty good area.