Information about mechanical rock properties is essential when tight reservoir is to be stimulated using hydrofracturing technique. The brittle area has to be considered as a priority region for determining the location of hydrofracturing initiation. Seismic data are commonly used to estimate the geomechanical properties such as brittleness average from elastic properties: Poisson’s ratio and Young’s modulus. This paper discusses the process of brittleness estimation based on elastic properties, which can be derived by inverting the pre-stack seismic data that can produce acoustic impedance, shear impedance, and density simultaneously. Novel methods, scaled inverse quality factor of P-wave (SQp) and scaled inverse quality factor of S-wave (SQs) attributes, have been used for identification of brittleness, fracture density, and hydrocarbon bearing in the fractured basement reservoir. The effectiveness of the proposed method has been tested in the field, which is consistent with fracture density log from formation micro-imager (FMI) log and hydrocarbon column data. The result showed that there is a significant correlation between brittleness, estimated from elastic properties, and fracture density logs. New attributes, the SQp attribute is potentially to be used as a fracture density indicator, while SQs attribute indicates the existence of hydrocarbon, which is confirmed with neutron porosity-density logs.
Part of the book: Exploitation of Unconventional Oil and Gas Resources
Ground-penetrating radar or georadar is a popular method in engineering and archeology for investigation of objects in shallow subsurface at high resolution. Georadars produce electromagnetic waves which propagate into the subsurface, and its interaction with the dielectric contrast is reflected and recorded in the radargram. It is an environmentally safe and nondestructive method and can be used for monitoring of active faults in the landslide-prone regions. This chapter explains the concept of georadar and its implementation on the detection of the active fault—Lembang fault—located in Bandung, Indonesia. Bandung is a highly populated city with many living around the active fault which poses a high risk of landslides. The Lembang fault was created by tectonic forces during the Pleistocene and has been constantly reactivated by recent volcanic events. It is the largest active fault in West Java, Indonesia, which is located in the midst of a densely populated urban area. A georadar survey using 25 MHz and 50 Hz frequency antenna was conducted to detect the fault in the urban setting. Unix-based seismic software was used to process the electromagnetic signals. The results showed that the georadar method was successful in identifying the active fault with clear imaging of the subsurface structures and basement of the region.
Part of the book: Earth Crust