Integrated NMR and Density Logs For Evaluation of Heterogeneous Gas-Bearing Shaly Sands

Abstract

Petrophysical properties evaluation of heterogeneous gas shaly sands reservoirs is one of the most difficult problems. These reservoirs usually produce from multiple layers with different permeability and complex formation, which is often enhanced by natural fracturing. Therefore, using new well logging techniques such as nuclear magnetic resonance (NMR) or a combination of NMR and conventional openhole logs, as well as developing new interpretation methodologies are essential for improved reservoir characterization. NMR logs differ from other conventional logs. Integration of NMR logs, density logs, and core data shall minimize uncertainties in the determination of formation porosity, permeability, and capillary pressure curve. The authors concentrate on determination of three petrophysical parameters of heterogeneous gas sand reservoirs: (a) determination of DMR porosity, ΦDMR, which is deduced from NMR porosity and density porosity; (b) NMR permeability, KBGMR, which is based on the dynamic concept of gas movement and bulk gas volume in the invaded zone; and (c) capillary pressure, which is derived from relaxation time T2 distribution.