Laminated Shaly Sand Reservoirs - An Interpretation Model Incorporating New Measurements

摘要

The measurement of anisotropic properties provides valuable information to accurately characterize shaly-sand laminated reservoirs. A petrophysical model, capable of combining both isotropic and anisotropic formation properties is required for true reservoir characterization. We propose an interpretation model that allows for a joint interpretation of logging data, including NMR, the newly available multi-component resistivity measurements, conventional logs such as gamma ray and density, as well as permeability data from wireline and/or drill-stem formation testing. The proposed petrophysical model relates the isotropic and anisotropic formation properties with those describing the properties of the sand fraction. The measurements handled by the model consist of total porosity, total shale volume, lithology indicato(s), NMR derived fluid distribution, and formation permeability. The mathematical equations describing the petrophysical model are coupled through a set of carefully selected formation parameters reflecting both the bulk formation properties and the properties of the sand fraction itself. The combined interpretation of the measurements yields, at each depth level, the relative abundance of shale and sand, the shale distribution: laminar, dispersed, structural and, more importantly, a set of unproved reservoir property estimates, including sand effective porosity, sand fluid saturations; both irreducible and movable, and sand permeability. Results from the proposed model reduce reservoir uncertainty and minimize the possibility of missing reservoirs not easily detected using conventional techniques. The paper describes the mathematical formulation of the petrophysical model as well as the applied numerical techniques. Optimal interpretation results are achieved utilizing forward modeling and a constrained, quality-weighted error minimization technique, which also generates parameter confidence intervals based on a sensitivity analysis. Synthetic and real field data examples are presented showing the ability of the interpretation model to derive the true reservoir character in laminated sand-shale environments.