1. A method, comprising: placing an NMR system downhole; obtaining nuclear magnetic resonance (NMR) data for a subsurface geological formation; correcting at least a portion of the NMR data to produce corrected NMR data; determining a NMR-based estimate of formation porosity using the corrected NMR data; obtaining dielectric permittivity data for the subsurface geological formation; determining a dielectric permittivity-based estimate of the formation water-filled porosity using the dielectric permittivity data; using the determined estimates for a more efficient drilling or production operation; in one or more processors, determining a gas volume using the determined NMR-based estimate of the formation porosity and the determined dielectric permittivity-based estimate of the formation water-filled porosity; and using the determined estimates for a more efficient drilling or production operation; wherein the formation water-filled porosity indicates a percentage of pore volume of the subsurface geological formation filled with water.