No abstract

Cibaliung is an area that is traversed by the Au-Ag-Cu mineralization pathway from low to intermediate sulfide epithermal system. The implemented techniques for delineating probable gold deposits by the lithology contact and structures that control epithermal gold mineralization systems in the area include first vertical derivative (FHD), vertical derivative (VD), second vertical derivative (SVD), analytic signal (SA), and tilt angle (TA). The results shows that high continuity of anomaly contrast in the direction of Northwest (NW), North-Northwest (NNW), and North-Northeast (NNE) is presumed to be the target geological structure of the study area. Furthermore, the contrast value of magnetic anomaly represents the lithology contact lies in the direction of the West and the East of the area.

Porosity and permeability of the reservoir rocks can be calculated using digital rock physics. This technique is one of the fastest and effective ways to calculate the value of porosity and permeability based on rock sample images. The samples observed in this paper were gathered from the outcrop of oil-filled sandstone formation. The technology of digital rock physics allowed us to predict the physical properties, mainly porosity and permeability, in the outcrop sandstone samples. The digital image model displayed in the 2D and 3D images and the complexity of pore geometry as well. From the image, we develop the digital simulation to predict the value of porosity and permeability in the 3D samples. By applying this method, we have confirmed that the target area of this research is potential to be a reservoir, which is porous and clean.

Indonesia is known for its large potential of shale resources, yet the character of their physical properties remains unclear. This study focuses on how to assess the petrophysical properties of shale using conventional wireline logs. Shale has been largely known as a host rock producing hydrocarbon in the conventional petroleum system due to the amount of kerogen trapped during the depositional process. The kerogen or continuously called Total Organic Carbon (TOC) behaves like a porosity to a density log and this will be misleading to the higher porosity than the actual shale rock. Prior investigation evaluates the physical properties in shale rock, including shale porosity, TOC, and matrix mineralogy, at a certain limited depth. A solid rock is presumed to consist of a shale matrix and TOC. Meanwhile, shale porosity is contained only in water. TOC responses to sonic wave, density, and porosity logs. We calculated the experimental data to estimate the volume of TOC at the limited depth to obtain the correlation of available logs. Shale porosity is then computed using a density log with the TOC-influence removed. The results show that the shale porosity is to be TOC-free with a value range of 3-14%.

The rock physics model is one effective yet challenging way to investigate the coal-seam gas potential in Indonesia. However, because of the complex conditions of the Coal-Seam Gas Reservoirs, it is difficult to establish models. Despite the scarce modeling, this study aims to estimate the relation of gas-saturated within pores of coal seam to the elastic properties of rock, which is P-wave velocity. First, the coal seam minerals are applied to quantify matrix moduli using the Voigt-Reuss-Hill Average method. Pride’s simple equation is used to estimate the elastic properties of the coal seam at dry condition (zero gas saturation). Finally, Biot-Gassmann’s theory is applied to determine the elastic properties of coal seam with fully gas saturated. As the result, the proposed model showed that there is a significant negative correlation between gas content with both density and P-wave velocity of the coal seam. Finally, this P-wave velocity model of gas-saturated coal seams should be properly useful as the quick look for identifying coal seam gas potentials.