Identification of Sweet Spots and Seismic Fractures in Tight Gas and BCGS Reservoirs

Seismic identification of fractures and sweet spots in tight gas reservoirs (TGR) and more specifically in basincentered gas systems (BCGS) using conventional 3D data is a challenge to its intrinsic resolution, especially in land surveys, where noise levels are generally high. Methods of detection of structural continuities and discontinuities, mainly faults, have been described in the literature for the detection of fractures, with different levels of success. Amplitudes and their attributes for geometric and textural interpretation are applied to predict gas reservoirs and brittle zones. Over the past 40 years, different seismic techniques have been developed to identify fractured regions and several processes applied for regions where low permeability gas reservoirs are expected. TGR related to some of the largest natural gas resources are considered yet to find around the world. Once identified such reservoirs, the main challenge for gas production is the low permeability of the rocks. Their petrophysical facies may show important variations related to the permeability due to heterogeneities in the spatial distributions of their natural fractures. Knowledge about the occurrence of natural fractures can help to define the sweet spots, which can vary along a basin, and optimize the positioning of producing wells. Several geological parameters to explain the performance of the best producers have been observed by a large number of authors. Some of these parameters can be supported by 3D seismic amplitudes in their assessments. In this work are presented some concepts of seismic amplitude interpretation that can be used on the definition of sweet spots associated to the best amplitude facies of TGR and BCGS with the largest probability of understanding fracture networks that can be key factors in the control of their permeabilities and conditions for production stimulation.