Use of the NMR and Resistivity Logs to Quantify Movable Hydrocarbon; Solution for the Tight and Low-Resistivity Carbonate Reservoirs

Abstract

Until an accurate fluid saturation tool is designed, the lack of a solid link between the petrophysical properties of reservoir rock and fluid is a real problem. The reservoir water saturation models are normally based on the standard Archie model to calculate fluid volumes. However, in tight carbonate reservoirs with heterogeneous wettability this model may present unrealistic results for the fluid volume (e.g., water/oil/gas) estimates. An integrated model using resistivity and NMR logs is introduced to quantify the movability of hydrocarbons in the reservoir transition zone. Pay zones may be missed in low-resistivity reservoirs (i.e., transition zones) due to the high water volume estimated from conventional logs. New synthetic resistivity logs are made in both the invaded and non-invaded zones based on assumptions made on the basis of pore and fluid interaction in the NMR log T2 distribution. The differences between the original and synthetic resistivity logs in connection with other log data are dominant signatures of the fluid volumes and movability in the formation. The new approach is developed on basis of exploration well data from a complex and heterogeneous carbonate reservoir in the Norwegian Barents Sea. The estimated fluid movability results are in agreement with the wireline formation tester (WFT) measurements of the well. This model, in addition to the transition zone, can also be applied for hydrocarbon bearing intervals which contain connate water. This approach shows that the reservoir wettability signature can also be identified by comparing the measured and constructed resistivity logs.

Microscopic Oil Displacement Mechanism of CO2 in Low-Permeability Heterogeneous Glutenite Reservoirs in the Junggar Basin

“…The T 2 relaxation distribution could be converted into the pore radius distribution according to certain conversion. , Therefore, the T 2 distribution actually reflected the distribution of pore size.…”

A New Method for Mobility Logging Evaluation Based on Flowing Porosity in Shale Oil Reservoirs

“…As an efficient tool for reservoir characterization, NMR logging should be calibrated with laboratory measurements to define appropriate parameters for evaluating petrophysical properties [24,25]. The combination of NMR and conventional well logs can be used to quantify hydrocarbon mobility [26]. New resistivity log data can be reconstructed based on the pore size distribution and fluid type interactions from the NMR log T2 distribution to determine mobility, which is dependent on the differences between synthetic and primary resistivity logs [27].…”