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An integrated seismic sequence stratigraphy and facies analysis has been carried out with a view ... more An integrated seismic sequence stratigraphy and facies analysis has been carried out with a view to understanding the depositional environment and stratal stacking pattern of Nandy Field of Niger Delta. Well logs and biostratigraphic information were used to identify the lithologies, stratal stacking patterns, stratigraphic surfaces, system tracts and reservoir potentials of the field. Seismic sequence stratigraphy and seismic reflection patterns were used to identify the seismic facies. Facies-related attributes were employed to identify the continuity and amplitude of seismic events. Three seismic facies packages and three reservoir sands were identified. The environments of deposition of the area consist of marginal marine to continental depositional settings predominantly made of shoreface deposits with few channel sands. The depositional model of the area shows that the deposition went down the axis of fluvial depositional system, which transports sediments through channels down to the shelf into the base of the slope down the basin. The seismic reflection patterns in this field are parallel to divergent reflections, high-continuity and high-amplitude facies, low-amplitude facies, low-continuity and variable-amplitude reflections, chaotic reflections and wavy reflection patterns. The seismic stratigraphic analysis of this field revealed the presence of low stand system tract (LST), high stand system tract (HST) and transgressive system tract (TST). Sands 1 and 2 were delineated within high stand systems tract (HST) while sand 3 was within low stand systems tract (LST). The results of this study show that the Nandy Field was of high hydrocarbon potentials and highlight the importance of using seismic reflection parameters (reflection configuration, amplitude, frequency and continuity) in the division and classification of seismic facies. Introduction Seismic stratigraphy and facies analysis are essential component of the present day exploration and in the development of oil and gas plays. A huge aspect of the value of seismic facies analysis depends however on whether or not local geological factors have been taken into account correctly. Interpretation of sand-shale depositional facies from seismic reflection data is based on a procedure known as seismic facies analysis [1]. It involves the delineation and interpretation of reflection configuration and other seismic parameters within the seismic-sequence correlation framework. These parameters that are reflection configuration, amplitude, continuity, frequency and interval velocity are interpreted to express certain gross lithologic, stratification, and depositional features of the sediment generating the cycle [1]. Reflection configuration reveals the gross stratification patterns from which depositional processes, erosion and paleotopography can be interpreted. Reflection amplitude contains information on the velocity and density contrasts at individual interfaces and on the extent of

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This study was carried out to estimate the effect of shaliness on water saturation from TN field ... more This study was carried out to estimate the effect of shaliness on water saturation from TN field of Niger Delta. The conventional Archie and the Shaly-sand water saturation models were used in the evaluation of wells. Two sand layers (Sand 01 and 02) were mapped with thicknesses range from 76.8ft to 119.3ft across the three wells for Sand 01 and 187.5 to 339.9ft across wells TN_1 and TN_4 for Sand 02. The cross plot of the effective porosity (φe) versus volume of shale (Vsh) that was carried out, reveals a decrease in the effective porosity with an increase in shale volume. This depicts a laminated shale pattern across the entire reservoir sands. The petrophysical estimation of water saturation from the conventional method and the Shaly-sand models of Simandoux and Indonesia, show a clear disparity in water saturation. This disparity recorded, was attributed to the degree of shaliness that is associated with the reservoirs, suggestive of over estimation of water saturation of the reservoirs by the conventional model.

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Depositional environments are characterized by their sedimentary lithology, sedimentary structure... more Depositional environments are characterized by their sedimentary lithology, sedimentary structures, paleocurrent patterns and fossils. Sedimentary facies are bodies of sediment that originate simultaneously in adjacent depositional environments. Such environments can be reconstructed using core data, well log information, and outcrops, and other available geologic information. In a study of four oil wells, depositional environments were inferred from the gamma ray log shapes identified on the gamma ray log motifs in combination with the density-neutron trends principle and sonic log high or low spikes. The Multi-Regressive Graph-Based Clustering approach was also used to compliment interpretations. The results obtained show that sand bodies that display an aggradational stacking pattern may be inferred to be channel sand deposits, regressive barrier bars, prograding delta deposits, and alluvial/ fluvial channel, or of transgressive shelf sand. A combination of Multi Regression Graph –Based Clustering and well log motifs has thus been shown to be a reliable tool in depositional environment reconstruction and lithofacies prediction.

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