Method and apparatus for measuring total nuclear magnetic resonance porosity

A method and apparatus for measuring total nuclear magnetic resonance porosity of an earth formation traversed by a borehole is sensitive to fast relaxation times that can be associated with clay-bound water. The total porosity measurement includes, in addition to free fluid and capillary-bound porosity, the porosity of clay-bound water and microporosity. An oscillating magnetic field is produced within the borehole, according to a phase alternated sequence, such as the Carr-Purcell-Meiboom-Gill (CPMG) sequence or a similar pulse sequence, to induce signals in the volume of formation which are measurable by the NMR logging tool. A reduced echo spacing and improved signal-to-noise ratio allows the recovery of short T2 components. The spin echo signals are measured and a value is determined for each signal. The signal values are separated into a first set and a second set wherein the first set comprises the early-time echo signals and the second set comprises the remaining echo signals. The second set of echoes are sub-divided into a plurality of groups and a window sum value is generated for each group of the second set, thereby producing a plurality of window sums. An attribute of the formation is determined based upon the plurality of window sums and the value of each signal of the first set.