There is general agreement across industry regarding the importance of thermal maturity as one of the key parameters defining core areas in unconventional plays. In such plays, the process of organic maturation has implications for both source and reservoir potential. From a source rock perspective, as thermal stress increases, the organic matter is transformed from kerogen to hydrocarbons. Type and quantity of the hydrocarbons generated is a function of kerogen type, organic richness, and thermal maturity. In commercial unconventional plays, type II kerogen is predominant, and maturity becomes a determining factor. Thermal maturity also influences the rock's reservoir quality, as unconventional units are both source and reservoir. There is a fascinating relationship between the transformation of organic macerals, mineralogic assemblages, and changes in fluid storage capacity.
It is difficult to quantify the effect of maturation on source and reservoir properties when evaluating a natural dataset, mostly due to the large number of variables that may play a role in the transformation of the rock through time (variations in tectonic stress and geothermal gradients, presence/absence of water, stratigraphic framework, etc.).
The purpose of this study is to evaluate the impact of thermal maturation on key geochemical parameters (e.g., TOC, HI), fluid properties, and organic/inorganic porosity under a laboratory-controlled environment. The sample suite used is comprised of three thermally immature, type II-kerogen-rich shales. Prior to the initiation of the artificial maturation experiment, the samples were subject to a detailed analytical protocol to characterize them in terms of kerogen type and quality, original porosity (i.e., petrographic and ion-mill/SEM characterization), and vitrinite reflectance. Samples were processed using hydrous pyrolysis. Rock residues were examined to evaluate the effect of the increasing temperature on the chemical, mineralogical, and petrographic properties as the samples transitioned from thermally immature to mature to post-mature (gas window). Fluids generated from each maturity stage were also collected for detailed geochemical characterization, including GC and isotopic measurements.
Results of this ongoing study provide a unique opportunity for evaluation of thermal stress on unconventional units both in terms of source quality and reservoir properties.