Abstract
The formation evaluation of Saudi Arabian tight gas reservoirs presents multiple challenges. The targeted gas resources discussed in this paper include both conventional and unconventional reservoirs. The complexities encountered include varying mineralogy, facies and mechanical properties, wide ranges of porosities and pore types, hydrocarbon viscosity, and variable formation water salinities. Major petrophysical uncertainties exist, including clay structure, variation of grain size distribution, electrical properties, and water salinity, that can be resolved by determining better data interpretation techniques and customizing the workflow for such reservoirs.
This paper presents interpretations from two wells within the same reservoir, based upon combining the geochemical, nuclear magnetic resonance (NMR), and conventional logging measurements. The integration of NMR data acquired with conventional logs is shown to be beneficial for the identification and quantification of hydrocarbon-bearing reservoirs and provide valuable information about porosity, relative permeability, and reservoir quality to be used for a fracturing assessment. The mineralogy and porosity information are obtained from geochemical and nuclear logs. By combining the mechanical properties results with the geochemical and NMR log total porosity interpretation, fracture parameters, such as Poisson's ratio, Young's modulus, and fracture closure pressure, can be obtained and a better fracturing job can be performed.
The case study results from these two wells demonstrate how to use and integrate all the available data, including the mud logs, to understand the reservoir behavior and to generate a workflow for future wells. This process includes optimizing the NMR activation scheme and using laboratory data to define a model for determining the T2 cutoff. Finally, rock mechanics laboratory measurements are required to develop and validate the fracture parameters prediction model.
