The North American hydrocarbon supply market has been transformed by recent discoveries in regionally continuous reservoir units consisting of shale and tight sands. Effective porosity values in these reservoirs average as low as 2% to 6% with nanoDarcy permeability in situ. Classical means of determining resource-in-place values in these unconventional formations involves integrating core and log analysis methodologies, where numerous levels of uncertainty exist. Controlled pressure coring operations were conducted on a sequence of wells drilled into various maturity windows in the rapidly emerging liquids-rich Duvernay Shale through the course of 2011 and 2012. Capturing critical resource-in-place parameters and conducting quantitative analysis of volatile hydrocarbons contained within the cored interval required the development of new field and laboratory methodologies. These procedures represent the only currently available workflow capable of directly capturing and analyzing reservoir hydrocarbons from core material. Field operations and core preservation steps were developed to maintain the integrity of the hydrocarbon system during shipping and core processing. Additionally, a laboratory methodology was developed for preserving and extracting liquid hydrocarbons from core material. By quantitatively recombining these extracted fluids with volatile hydrocarbons captured from the controlled pressure coring operation, in situ PVT behavior of this single-phase volatile oil/condensate reservoir can be determined. As a result, recombined fluids can be compared to production samples for the purpose of studing pore scale mechanisms affecting production. Key breakthroughs were made during all stages of the workflow, and it was determined that core capture and surface handling operations are just as important as developing the new laboratory techniques required to understand resource uncertainty, effective fluid mobility, and PVT behavior. This paper describes and documents the key advancements made in coring operations and specialized core analysis, as well as their role in accurate quantification of hydrocarbons in place and the determination of in situ PVT behavior of the Duvernay Shale.
Shale gas reservoir quality evaluation is a technical challenge as conventional log interpretation methods and even core measurements may be inadequate or inaccurate. Only through a robust integration of core and logs data, a reliable estimation of the gas in place can be obtained and the interval with the best petrophysical and geomechanical characteristics (sweet spot) identified. Total GIIP estimation is derived from core and log analyses and can be complemented by measuring desorbed gas from selected core samples. Total gas content is the combination of measured and estimated gas components: lost gas, desorbed gas and residual gas. Lost gas is the most critical component being usually extrapolated from desorbed data to time zero using linear and/or polynomial curve fitting. Total gas can now be directly measured by using a new controlled pressure coring technology able to capture a full sized core and retain all the hydrocarbons contained in the rock, eliminating gasses and/or liquids lost during conventional coring techniques. The characterization of the lower Barnett Shale described in this paper was achieved by coring the whole sequence: several samples from conventional cores were taken for desorption analysis and three pressure cores were placed to target the main shale facies identified from the integrated reservoir model. Core gas data from both desorption and pressure coring were integrated for a more reliable total gas estimation; consistent relationships among handling time, gas content and method used for deriving lost gas were also observed. Obtained total gas values were in good agreement with calculated gas volumes from logs. In addition, the combined application of pressure coring and desorption analysis in the Barnett Shale has allowed to improve well site procedures for optimal core data acquisition and to define the best approach for a robust shale gas evaluation.
The industry is challenged to accurately determine the total hydrocarbon composition and saturations in both conventional and unconventional reservoirs. Several attempts in coring technology advances have been employed in the past with limited success. These attempts include methods to collect expelled pore space fluids and gases for further analysis. The attempts have resulted in technologies that provide limited core in terms of length and diameter, low recovery percentages, poor success ratios and complicated core processing. Pressure coring itself has been viewed as a solution but introduces inherent safety concerns by bringing high-pressure systems to the surface. The combination of poor reliability and safety risks has resulted in infrequent use of the various technologies and methods to analyze pore fluids and gases. A new tool has been developed to overcome the safety concerns, simplify core processing and provide the means for quantitative answers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.