System and method for clay typing using NMR-based porosity modeling

A method for determining petrophysical properties of geologic formations containing clay materials, comprising:

• (a) providing a model of the geologic formation, said model comprising a wetness parameter for that fraction of the characteristic volume of adsorbed water in a given mineralogy component, which is proportional to the volume Vclay of that component;
• (b) providing log data corresponding to the geologic formation;
• (c) performing constrained inversion of the provided data log using the model of the geologic formation;
• and
• (d) determining petrophysical properties of geologic formations based on the provided model and the performed constrained inversion,
• wherein the wetness clay parameter is defined as:
• wetness_clay=Phi_NMR_clay/Vclay.

A method for determining petrophysical properties of geologic formations containing clay materials, comprising:

• (a) providing a model of the geologic formation, said model comprising a wetness parameter for that fraction of the characteristic volume of adsorbed water in a given mineralogy component, which is proportional to the volume Vclay of that component;
• (b) providing log data corresponding to the geologic formation;
• (c) performing constrained inversion of the provided data log using the model of the geologic formation;
• and
• (d) determining petrophysical properties of geologic formations based on the provided model and the performed constrained inversion,
• wherein step (b) comprises providing NMR log data, and wherein NMR porosity of the clay materials is modeled in step (a) as having one component due to adsorbed water on clay surfaces (Phi_NMR_clay) and a second component due to bulk fluids occupying pores of all sizes (Phi_NMR_bulk), and wherein the component due to the adsorbed water Phi_NMR_clay attains a maximum in the case of the water saturated pure clays and is linearly proportional to the volume of clay in the formation.

A geological formation interpretation system comprising:

• means for providing a model of a geologic formation, said model comprising a wetness parameter for that fraction of the characteristic volume of adsorbed water in a given mineralogy component, which is proportional to the volume Vclay of that component;
• means for providing log data corresponding to the geologic formation;
• processor means performing constrained inversion of the provided data log using the model of the geologic formation;
• and
• means for determining petrophysical properties of geologic formations based on the provided model and the performed constrained inversion,
• wherein the means for determining petrophysical properties comprises means for determining a generic log according to:
• LOG = ∑ i = 1 log ⁢ ⁢ s ⁢ ⁢ ( Vmat * LOG ⁢ ⁢ mat i + ∑ j = 1 clay ⁢ ⁢ Vcl j * LOG ⁢ ⁢ cl ij + phie * LOG i ⁢ w )
• where, LOG is the generic log, the i-index runs over the different logs available, such as gamma, bulk density, thermal neutron and NMR;
• Vmat is the matrix volume;
• Vclj is the volume of the j-th clay mineral and the clay index j corresponds to a typical clayey sandstone consisting of quartz and other minerals and common sedimentary clays, Phie represents pores of all sizes containing water in bulk form;
• LOGmat, LOGclij and LOGiw are the corresponding log parameters for the matrix, clay and bulk water respectively.