An overview of research trend in geochemical and petrophysical technique of shale and tight reservoirs

Abstract

Shale reservoirs has drawn great attention among unconventional resources since the first unconventional extraction of gas from Barnett Shale by Mitchell in 1998. In the beginning, carpet drilling and hydraulic fracturing to shale reservoirs made a great benefit without detailed geological understanding. However, the sudden increase of gas supply and international economic crisis resulted in lower gas price relative to oil price, which requires more detailed development optimization and geological characterization on shale reservoirs to reduce operation cost. In order to evaluate the productivity of shale and tight reservoirs, it is necessary to accurately predict the amount of gas stored in the reservoir. To calculate exact volume of gas in reservoirs, we must reliably measure petrophysical parameters such as permeability, porosity, and water saturation to estimate free gas volume, and geochemical parameters such as total organic carbon (TOC) and adsorption capacity to estimate desorbed gas volume. Several measurement techniques have been proposed to overcome the difficulty in very low porosity and permeability of shale and tight reservoirs. Recently, the crushed rock technique have been used for porosity and permeability of shale and tight reservoir are measured, but the standard procedures have not yet been established. Water saturation is another hurdle since actual measurements are extremely difficult and time-consuming. Modified conventional equations have been tried, but there are still various limitations. We also cover currently available techniques and their limitations on TOC, a measure for gas generation potential, and adsorption capacity. Currently, measurement techniqies for petrophysical and geochemical properties of shale and tight reservoirs are not fully established. There should be detailed studies for the accurate estimation of these properties, which can lead successful reservoir characterization.