Reservoir fluid determination from angle stacked seismic volumes in ‘Jay’ field, Niger Delta, Nigeria

Abstract

ABSTRACT:The study was carried out to investigate the dissimilar seismic amplitude responses observed in sandstone reservoirs with the same fluid saturation. This challenge now informed the analysis of different amplitude responses from the 'Jay' Field in order to verify the reservoirs fluids around and away from well location based on the integration of Amplitude Variation with Angle (AVA) and seismic inversions. The well log data provided were used to identify hydrocarbon bearing zones and Poisson Ratio analysis. Anomalies from the AVA analysis were investigated using the elastic impedance inversion of the near and far volumes. Crossplots of Lambda-Mu-Rho inversion were produced to relate reservoir incompressibility and rigidity modulus for lithology and fluid determination. Sand E exhibited amplitude increase with angles at well point and also away from well location (red triangle). The approximate elastic impedances of the inverted seismics are almost similar to the log estimates, an indication of good correlation. Integration of incompressibility (Lambda-Rho) and rigidity (Mu-Rho) modulus analyses reveals the presence of gas saturation in reservoir Sand G because low Lambda-Rho coincides with high Mu-Rho from both log estimates and inverted seismics. In the case of Sand D, high Lambda-Rho coincides with high Mu-Rho because it is oil saturated. This study has helped to differentiate the fluids in Sands D and G despite having similar AVA responses. The methods adopted in this work can be useful in hydrocarbon detection from seismic data in fields with similar geological setting. Seismic inversion technique helps in the determination of reservoir properties away from well location (Simm, 2005). For instance, inverted seismic data enhances the identification of subtle properties in conventional seismics (Contreras et al., 2006). Reservoir properties between wells can be determined from inverted seismic results. This was demonstrated by Adekanle and Enikanselu, (2013) where the vertical and lateral extent of rock properties such are porosity, lithology and density were determined. However, seismic data have limited frequency content such that thin layers may not be resolved (Simm and Bacon, 2014).The integration of high frequency log information with seismic data in model based inversion was adopted to mitigate this effect. Moreover, model based inversion technique of iterative forward modeling and comparison procedure does not suffer from defective wavelet and over simplification of the subsurface associated with recursive and sparse spike inversions methods respectively (Cooke and Schneider, 1983;Veeken and Da Silva, 2004;Simm and Bacon. 2014).The integrated approach of Lambda-Mu-Rho inversion and Rock Physics modeling by Ekwe et al., (2012) was used to delineate hydrocarbon charged reservoirs in a Niger Delta field. In gas hydrates region where well information is most often sparse, Amplitude Variation with Angle (AVA) was the method used for free hydrate gas assessment as discussed by Javaherian et al., (201...

How to Estimate the Major Petrophysical Properties: A Review

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Fluid and Lithology Discrimination for Reservoir Characterization of HAX Field, Offshore Niger Delta

“…Murho and density are both lithology discriminators but density can also be used for fluid prediction, this is one of the advantages of density over Mu-Rho has seen from the crossplots [33]. In theory, sand will have a high value of Mu-Rho and a low value of shale [38] but in this field, the results of the cross-plots show that the Mu-Rho values are high for shale and low for sand while the density of shale is higher than that of sand [2,33]. Furthermore, hydrocarbon bearing sand is less dense than brine (even as hydrocarbon gas is less dense than oil) and brine is less dense than shale [2,33].…”

Multidisciplinary Characterization of Unconventional Reservoirs Based on Correlation of Well and Seismic Data

“…Furthermore, the recently developed rock physics template (RPT) technique [36] can estimate the fluid and mineralogical content of a reservoir rock on a cross plot of Vp/Vs ratio against the AI of a P wave (Figure 2). This method has been described in numerous publications [2,11,13,[32][33][34][35][36][37][38][39][40], including focused studies of elastic parameter recognition and RPT analysis of Polish shales [3,4,10,21,[41][42][43]. The process of successfully integrating data at different scales represents the biggest challenge in generating detailed 3D models of reservoirs.…”

“…The process of successfully integrating data at different scales represents the biggest challenge in generating detailed 3D models of reservoirs. In response to this problem, some studies have applied the RPT technique to multi-scale laboratory data, well log data, and seismic data [37][38][39]43], though further research is required to determine best practices for this technique. Here, we report the results of multidisciplinary characterization of an unconventional reservoir based on relationships between various reservoir parameters in 1D, 2D, and 3D.…”