Integrated Reservoir Characterization and Completions Design Using Petrophysical and Acoustics Logs in Unconventional Tight Formation

Abstract

With all the conventional reservoirs being almost exhausted around the world, our immense dependency on unconventional reservoirs has led us to look for measurements that are beyond conventional way. In the optimal exploitation of unconventional reservoirs, integrated Petrophysical and Geomechanical studies provide the best means to both 1) evaluate formation properties such as fluid types, volumes and flow potential, and 2) use this information along with rock's mechanical properties to optimize completions program and maximize production. While a basic petrophysical study can be made using triple combo logs gamma ray, neutron porosity, density and resistivity - for reconnaissance and quick look, such studies are not enough for the purpose of completions and production optimization in unconventional. A combined study using different petrophysical, geological and acoustic logs is used in order to answer the questions and problems faced during characterizing a tight unconventional reservoir. The answer products from these will help in advanced studies which would include reservoir characterization and completion design. For that, we would need to bring in acoustic measurements to determine rock types and respective mechanical properties, which would be influenced by fracture, anisotropy, stress direction and permeability of the formation. Spectroscopy logs will further add to knowledge of the lithology at mineral level, required for petrophysical evaluation and rock physics modeling. Today advanced spectroscopy logs also measure Total Organic Carbon (TOC) percentage of the formation, important to understand source rock maturity and to determine true flow potential in tight formations. Images from Micro Imaging resistivity tool are important in unconventional to evaluate fractures which often times are the only source of permeability in tight rocks. Nuclear Magnetic Resonance is considered essential to determine fluid types, respective volumes and bulk permeability of unconventional formations. An integrated study using all the above measurements helps best combine Petrophysical and Geomechanical aspects of the formation under investigation. Furthermore, in unconventional reservoir evaluation, such a study helps us to determine stress barriers to hydraulic fracturing important to zone-wise design and optimize completions program. In this paper, we present a systematic procedure and corresponding results of an Integrated Petrophysics and Geomechanics study in an unconventional tight reservoir, which helped to 1) optimize hydraulic fracturing and completions program, and 2) create complete model of hydrocarbon production.