Applications of Petrophysical Scale Reconciliation to Saudi Arabian Reservoirs

Abstract

Abstract Core data from three fields have been stress-corrected and upscaled so that they become notionally reconciled with wireline well logs along wellbore axes. The upscaling process draws upon logging tool response functions in a way that optimizes the correspondence between the smoothed core porosity data and density or sonic logs. It is demonstrated that there are significant differences between core-derived porosities at the core and log scales. These differences are tool-specific, and they transmit through to the log-derived porosity. Once a scale-reconciled log-derived porosity has been validated, it can be input to a core-derived porosity-permeability algorithm. Where this transform is based on compatible, upscaled core data, the results are significantly better than those from the conventional approach that is tied back to the core-plug scale. These observations have formed the basis for improved workflows for the petrophysical evaluation of porosity and the subsequent estimation of intergranular permeability. The approach can be readily extended to the evaluation of water saturation where low-invasion coring has taken place. Introduction Core-to-log integration is a fundamental petrophysical component of integrated reservoir studies, because it provides the groundtruthing for well-log analysis. Historically, log responses have been tied back to core data with little attempt being made to take account of the different scales of measurement. More recently, however, there has been a renewed interest in redressing this situation, even though it is recognized that a full reconciliation of core and log data might not be possible, because of the different volumes of rock sensed by these two types of measurement. Success at this stage delivers further benefits when porosity is used as a predictor for the evaluation of other parameters such as permeability. In this paper, petrophysical scale reconciliation is examined from two specific standpoints. The first is to process conventional core porosity data so that they provide the best possible groundtruthing for the evaluation of porosity from density and sonic logs.