Since the discovery of major oil and gas reserves in carbonate rocks in the Middle East, carbonate reservoirs became important to the petroleum industry. Carbonate rocks have covered only 20% of the sedimentary rock records. However, carbonate reservoirs hold 50% of the world petroleum reserves. Arun Carbonate Reservoir is one of the biggest proven retrograde gas reservoirs in the world. After more than thirty years of production, Arun Carbonate Reservoir had an initial gas in place of 14.1 TCF residual hydrocarbon gas. The issue makes Arun Carbonate Reservoir became an interest to be studied for the development and production of hydrocarbon in other carbonate reservoirs in Indonesia. One of the fundamental topics to be studied is the characteristics of Arun Carbonate Reservoir itself. The characteristics of carbonate reservoir usually cause a lot of geologic and engineering problems in the development and production of hydrocarbon reserves. This paper aims to identify the characteristics of Arun Carbonate Reservoir and its implication to optimize the most potential gas resource zone in Arun Gas Field, Aceh, Indonesia. The data from sixteen wells have been examined through several multidiscipline studies: geophysics (well logging), geology (facies, lithology and diagenetic analyses), and petrophysics (core analysis). The result of this study shows that Arun Carbonate Reservoir (N5-N8) contains limestone 92%, 5% dolomite, and 3% dolomitic limestone (or other), and petrophysically have 16% porosity and 13.5 md permeability in average. Arun Carbonate Reservoir is divided into four facies (Reef, Near Reef, Lagoon, and Middle Shelf). Of four facies in Arun Carbonate Reservoir, only two facies which can be categorized as productive facies: Reef and Lagoon Facies. The potential zones of hydrocarbon resource have vertically been documented in Arun Carbonate Reservoir.

Mining activities related to excavation or landfill will always face problems with slopes, both in the form of working slope and final slope, in addition the groundwater factor in the rock layer increases the burden by filling pores and reducing friction inter-grain influences the slope stability. The slopes must be analyzed for stability to prevent landslide hazards because they involve work safety, equipment safety, and smooth production. PT. XYZ is a coal mining company located in the Lilin river, South Sumatra, planning to optimize and stabilize the final slope to a depth of 120 m. Geotechnical drilling has been carried out as many as 3 points with a total depth of 270 m and 80 samples of rock and soil testing. The results of optimization and stability of the slope by conducting dewatering at each elevation to obtain optimal slope conditions at PT. XYZ can be done up to elevation of -130 meters above sea level with a depth of 142 meters with an angle of 35° with the condition of the ground water level must be maintained at the halfway point of the slope (GWL Chart No. 3). Under water saturated conditions (GWL Chart No. 5) at the same elevation the permissible angle is only 25° with a final slope height of 136 m.