Petrophysical Properties Evaluation of Tight Gas Sand Resrvoirs Using NMR and Conventional Openhole Logs

ABSTRACT

Tight reservoir means reservoir of low porosity and low permeability. Many tight formations are extremely complex, produced from multiple layers with different permeability that is often enhanced by natural fracturing. The complicity of these reservoirs is attributed to a) Low porosity and low permeability reservoir, b) The presence of clay minerals like illite, kaolin and micas in pores, c) The heterogeneity of the reservoir in vertical and lateral directions. Evaluation of tight gas sand reservoirs represents difficult problems. Determination of petrophysical properties using only conventional logs is very complicated. Use of NMR in individual bases or in combination with conventional openhole logs and SCAL data leads to better determination of petrophysical properties of heterogeneous tight gas sand reservoirs.

This paper focuses on determination of three petrophysical parameters of tight gas sand reservoirs: 1) Determination of detailed NMR porosity in combination with density porosity, ΦDMR, 2) NMR permeability, KBGMR, which is based on the dynamic concept of gas movement and bulk gas volume in the invaded zone and 3) Capillary pressure derived from relaxation time T2 distribution and then it could be used for the saturation formation measurements especially in the transition zone.

Keywords: