An NMR-based model for determining irreducible water saturation in carbonate gas reservoirs

An NMR-based model for determining irreducible water saturation in carbonate gas reservoirs

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Abstract Unambiguously determining irreducible water saturation $$left({S}_{ m{wirr}} ight)$$ S wirr poses a formidable challenge, given the availability of multiple independent methods.Traditional approaches often depend on semi-experimental relationships derived from simplified assumptions.These methods, originally designed for oil sandstone reservoirs, result in varying $${S}_{{ ext{wirr}}}$$ S wirr values when employed in carbonate gas reservoirs.Nuclear magnetic resonance (NMR) is the most advanced technique for determining $${S}_{{ ext{wirr}}}$$ S wirr.While highly accurate, the NMR-based method necessitates the laboratory measurement Accessories of the transverse relaxation time $$left({T}_{2} ight)$$ T 2 cutoff.

Laboratory-based $${T}_{2}$$ T 2 cutoff determination is resource-intensive and time-consuming.This research aims to develop a robust model for determining $${S}_{{ ext{wirr}}}$$ S wirr in carbonate gas reservoirs by utilizing NMR well logging measurements and special core analysis (SCAL) tests.Various $${T}_{2}$$ T 2 cutoff values were initially employed to compute bound water saturation $$left({S}_{{ ext{bw}}} ight)$$ S bw at different depths to achieve this.Subsequently, Surcingles the data points $$left({T}_{2}, {S}_{{ ext{bw}}} ight)$$ T 2 , S bw were graphed on a scatter plot to unveil the relationship between $${S}_{{ ext{bw}}}$$ S bw and $${T}_{2}$$ T 2.The scatter plot illustrates an exponential decrease in $${S}_{bw}$$ S bw with increasing $${T}_{2}$$ T 2 , forming the basis for the $${S}_{{ ext{wirr}}}$$ S wirr model derived from this relationship.

Finally, the parameters of the $${S}_{{ ext{wirr}}}$$ S wirr model were fine-tuned using SCAL tests.Notably, this $${S}_{{ ext{wirr}}}$$ S wirr model not only accurately yields $${S}_{{ ext{wirr}}}$$ S wirr at each depth but also offers a dependable determination of the optimal $${T}_{2}$$ T 2 cutoff for the reservoir interval.