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Petrophysical Properties Evaluation of Tight Gas Sand Reservoirs Using Integrated Data of NMR, Density Logs and Scal
(1) Petroleum, KFUPM, Dhahran, Saudi Arabia.
Many tight formations are extremely complex, producing 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 and b) The presence of certain clay minerals like illite, kaolin and micas in poress. Evaluation of tight gas sand reservoirs represents difficult problems. Determination of petrophysical properties using only conventional logs 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 in individual bases or in combination with density log and SCAL data provide better determination of petrophysical properties of s tight gas sand reservoirs.
This paper concentrates on determination of three petrophysical parameters of tight gas sand reservoirs: First, 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, Second NMR permeability, KBGMR; it is based on the dynamic concept of gas movement and bulk gas volume in the invaded zone. It is concluded that KBGMR is facies independent technique and this is the most important value of this technique and Third Capillary pressure derived from relaxation time T2 distribution and then it 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.