Petrophysical properties evaluation of tight gas sand reservoirs using integrated data of NMR, density logs and SCAL. 9th Middle East Geosciences Conference, GEO 2010.

Many tight formations are extremely complex, producing from multiple layers with different permeability that is often enhanced by natural fracturing. The complexity of these reservoirs is attributed to: (1) low porosity and low permeability reservoir; and (2) the presence of certain clay minerals like illite, kaolin and micas in pores. Evaluation of tight gas sand reservoirs represents difficult problems. Determination of petrophysical properties using only conventional logs is very complicated. Nuclear magnetic resonance (NMR) logs differ from conventional neutron and density porosity logs. NMR signal amplitude provides detailed porosity free from lithology effects and radioactive sources and relaxation times give other petrophysical parameters such as permeability, capillary pressure, the distribution of pore sizes and hydrocarbon identification. Using of NMR on an individual basis or in combination with density log and SCAL data provides better determination of petrophysical properties of tight gas sand reservoirs. This study concentrates on determination of three petrophysical parameters of tight gas sand reservoirs: (1) Determination of detailed NMR porosity in combination with density porosity, DMR. It is found that DMR porosity method is a gas corrected porosity, and independent facies porosity model. (2) NMR permeability, KBGMR, is based on the dynamic concept of gas movement and bulk gas volume in the invaded zone. It is concluded that KBGMR is a facies independent technique, and this is the most important value of this technique. (3) Capillary pressure derived from relaxation time T2 distribution could be used for formation saturation measurements especially in the transition zone. It is found that the assumptions of capillary pressure approximation from T2 distribution can be applied in gas wells as well with some consideration due to gas and mud filtrate effects.