Application of Pressure Transient Well-Test to Geologic Reservoir Characterization of a Turbidite Reservoir in the West African Transform Margin Basin Offshore Cote d'Ivoire

摘要

Building static reservoir model that realistically captures facies heterogeneities relies on detailed interpretations of the sand body architectures from the integration of subsurface datasets and analogue examples.The delineation of stacked channelized turbidite sands was carried out,based on detailed petrophysical analysis,well log correlation and seismic interpretations.The continuity and connectivity of these sands remain a challenge despite having carried out detailed seismic attribute analysis for sand fairways mapping.For this study,we used a combination of well logs correlation and pressure transient analysis to resolve the sand connectivity and continuity challenges.Pressure transient analysis can be used to achieve both well productivity analysis and reservoir dynamic descriptive analysis.Interpretation of pressure transient well test can be done either by type curve matching or log-log derivative plot.A combination of log-log derivative plot and the Tiab Direct Synthesis(TDS)method were used to analyze the well test data.A log-log derivative plot is a plot of the pressure derivative against time with both axes on a logarithmic scale.Different geologic features such as faults,fractures and sand channels show unique fingerprint on the log-log derivative plots.The distance of the channel sand from the well was estimated using the Tiab Direct Synthesis method by making use of the gradient of the channel fingerprint on the log-log-derivative plot.The well test data from two wells at approximately 2.5km apart were plotted on the log-log derivative plot in other to identify the nature of the geologic features around the wells.In one of the well,channel sand signature or fingerprint was seen and the other well was not tested long enough to see the channel sand signature on the log-log derivative plot.The gradient from the channel sand signature on the log-log derivative plot was used in the TDS model to estimate the distance of the channel sand from the well.The TDS model estimated the distance of the channel sand from the well to be 51m.Based on the result of the pressure transient test analysis,we could establish that the sand is not continuously connected between the two wells.In combination with well logs correlation and seismic attribute analysis,the established sand fairways and baffles thus led to robust geological models with petrophysical properties that capture properly the lateral heterogeneity in the field.