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.
Channel identification using 3D seismic attributes and well logging in lower Shihezi Formation of Hangjinqi area, northern Ordos Basin, China
Abstract Channel identification in oil and gas exploration is a vital task due to the importance of fluvial reservoirs. The fluvial sandstone of Lower Shihezi Formation of Ordos Basin is the primary target layer of gas exploration and development which has the maximum potential of producing tight gas sand reservoir in China. Fluvial paleo-channels can be identified easily by core, outcrop and logs data, but due to development of the several faults and limited seismic resolution in the study area, it is difficult to identify them by conventional seismic methods. The study was conducted in Hangjinqi area on the regional level of about 4537.87 km2. The radical objective of this research is to recognize the horizontal distribution and geometry of the multiple channels. Based on the study of integrated analyses of geological cores, geophysical well-logs, and seismic attributes it is confirmed that multiple braided channels are present in the study area. Channel distribution based on seismic attributes and its overlapping on the paleogeographic map showed that the channels are coming from the North and are merging towards South direction.
Stratal slicing of Miocene-Pliocene sediments in Vermilion Block 50-Tiger Shoal Area, offshore Louisiana
Many people have viewed modern land surfaces from commercial airplanes and marveled at the form and geometry of geomorphic features such as river channels, deltas, barrier islands, and dune fields. These views represent complete images of the modern time surfaces. We can classify the depositional nature of features on these images by interpreting their planiform geometry and geographic context. In fact, modern 3-D seismic technology has made it possible for us to image similar, but much older, geomorphic or depositional features preserved in the rock record. Unfortunately, although many reservoir-scale (well-to-well scale) features can be detected in vertical seismic lines, few such features can be resolved and interpreted in the vertical perspective because of the data's limited bandwidth. Only in the horizontal perspective are such depositional features large enough to be resolvable when displayed in map view on geologic time surfaces.