Identification and Prediction of the High Heterogeneous Channel Sand in Southern Turgay Basin
With the development of high quality 3D seismic exploration in Southern Turgay Basin, the exploration targets are being shifted from the structural traps to stratigraphic traps. As for one of the most important reservoir, the identification and prediction of the high heterogeneous channel-sands is the key to enhance drilling success rate and reduce the investment risk. The multi-geophysical methods and integrated studies of geology and geophysics have been applied to determine the distributed area of the channel-sands in Southern Turgay Basin of Kazakhstan. The channel-sands are widely distributed from Upper Jurassic to Cretaceous. The channel-sands in the mature explored Cretaceous strata are meandering or braided river bars. On well-logging, the SP curve of the channel sand presents the block - shape and positive cycle with bell – shape with high porosity and permeability, and lower self-potential, gamma ray and density; Whereas in seismic profiles, channel sands presented the „bright spot‟ with the low frequency, high amplitude and short reflection. No obvious rules of „bright spot‟ can be found in the seismic profiles. The multi-geophysical methods, such as strata slice, 3D visualization and spectral decomposition, etc., have been applied to identify more than 50 pieces of channel-sands with the cutting and overlying each other vertically and horizontally. As for the relatively lower explored Upper Jurassic strata, the channel-sands developed in submerged distributary channel, branching mouth bars of deltaic system or fan deltaic system. On well-logging, channel sand presents the middle porosity and permeability, and lower selfpotential, gamma ray and density; Low-frequency and varied amplitude presents in seismic profiles. The area distribution of the deltaic or fan deltaic can be determined by sequence stratigraphy and the distribution of the channel-sands in different cycles vertically can be identified by chronostratigraphic interpretation in wheeler domain. Several cases suggested that the integration of strata slice, chronostratigraphic interpretation in wheeler domain, 3D visualization and spectral decomposition is an effective method to identify the high heterogeneous channel-sand, which has been confirmed by drilling results.
Predicting the gas resource potential in reservoir C-sand interval of Lower Goru Formation, Middle Indus Basin, Pakistan
Abstract The integrated study of seismic attributes and inversion analysis can provide a better understanding for predicting the hydrocarbon-bearing zones even in extreme heterogeneous reservoirs. This study aims to delineate and characterize the gas saturated zone within the reservoir (Cretaceous C-sand) interval of Sawan gas field, Middle Indus Basin, Pakistan. The hydrocarbon bearing zone is well identified through the seismic attribute analysis along a sand channel. The sparse-spike inversion analysis has efficiently captured the variations in reservoir parameter (P-impedance) for gas prospect. Inversion results indicated that the relatively lower P-impedance values are encountered along the predicted sand channel. To further characterize the reservoir, geostatistical techniques comprising multiattribute regression and probabilistic neural network (PNN) analysis are applied to predict the effective porosity of reservoir. Comparatively, the PNN analysis predicted the targeted property more efficiently and applied its estimations on entire seismic volume. Furthermore, the geostatistical estimations of PNN analysis significantly predicted the gas-bearing zones and confirmed the sand channel as a major contributor of gas accumulation in the area. These estimates are in appropriate agreement with each other, and the workflow adopted here can be applied to various South Asian regions and in other parts of the world for improved characterization of gas reservoirs.
Terrigenous Clastic Depositional Systems: Applications to Petroleum, Coal, and Uranium Exploration
Two experts in fundamental and applied sedimentology and sedimentary economic geology provide a state-of-the-art summary of clastic depositional environments and their associated mineral fuel deposits. Utilizing a multidisciplinary approach, the authors focus on the recognition, mapping, and three-dimensional reconstruction of clastic deposits, primarily from subsurface data, examine the hydrology of sedimentary basins, and discuss applications of genetic facies analysis to mineral fuel resource appraisal, exploration, and development.