Exploration Insights September 2019 | Page 20

20 | Halliburton Landmark Exploration Insights | 21 calculated to have been generated by the Lower and Upper Bakken source rocks, with 200 BBOE from the Lower Bakken and 280 BBOE from the Upper Bakken (Figure 3). These estimates are compared with published values in Figure 4. They fall at the upper end of those estimated by the USGS, and ~60% of the ultimate volumes expelled as predicted by Roller and Pepper (2018). This shows that the Bakken Petroleum System is a highly effective unconventional resource and is predicted to have relatively negligible loss of hydrocarbons. Volume of Generated Hydrocarbons (MMBOE) High Low © 2019 Halliburton Application When Data are Sparse Figure 3 > Volume of hydrocarbons generated from the Lower and Upper Bakken source rocks. The case study tested the workflow in a data rich area. In data poor areas, such as exploration frontiers, the workflow can be run based on the application of assumptions for the input data and maps, based on the prediction of the depositional environment, source rock type, and stratigraphic age. In these scenarios, knowledge from analogues will have to be leveraged. Lower and Upper Bakken source rocks had average original TOC values of 14.9 and 18.8 wt% and average original HI values of 320 and 395. These values are for the entirety of the source rock, including immature areas — the difference between present-day and original TOC and HI values will be greater than these averages imply where the source rocks are mature to post-mature. The source rock volume can be inferred from the depositional environment and distribution of organic rich sediments (as presented in Neftex GDE maps) and through utilization of Neftex Depth Analysis maps. Optimistic original TOC and HI values can be assigned based on typical The reduction in HI and TOC with maturity was used to estimate the volume of hydrocarbons generated at peak maturation (Figure 3). A total volume of >480 BBOE of hydrocarbons was Estimated Volume (BBOE) Data Source Lower and Upper Bakken source rocks Hydrocarbons generated 484.3 Neftex ® Insights Lower and Upper Bakken source rocks Oil in-place 4 – 171.7 Neftex Insights Lower and Upper Bakken source rocks Hydrocarbons generated 10 – 400 USGS from Jin and Sonnenberg (2013) Bakken and Three Forks formations Technically recoverable resource 7.38 USGS from Gaswirth and Marra (2015) Williston Basin, likely Bakken Formation sourced Known recoverable reserves in discoveries 6.08 Lower and Upper Bakken source rocks Ultimate expellable potential 814.0 Study Summary ® Rystad Energy UCube, version 2019-08-07 Roller and Pepper (2018) © 2019 Halliburton Figure 4 > Summary of the estimated generated hydrocarbon volumes, and the known oil reserves in the Bakken Petroleum System, from this and published studies. values associated with similar source rocks and expected kerogen type. In the reverse to the above case study, the present-day TOC and HI values can then be calculated by diminishing the values in areas where the source rock is predicted to be mature or post-mature. The maturity could be predicted based on the depth of the source rock and the application of modeled surface temperatures, geothermal gradients, or heat flows. be determined and carried through to the resulting volume calculated. SUMMARY Cornford, C. 1998. Source rocks and hydrocarbons of the North Sea. In K.W. Glennie (Eds.), Petroleum Geology of the North Sea – Basic concepts and recent advances 4th edition, p. 376-462. (XURBB_453032). The workflow and case study presented here demonstrate how widely available organic geochemical and geological data can be used in a series of calculations to estimate the volume of hydrocarbons generated and the amount of in-place petroleum preserved in accumulations. The workflow, or aspects of it, can be followed at any point in the exploration or appraisal process. It can be followed in data rich scenarios through the utilization of the standardized Neftex databases, compiled from public domain data, and in data poor scenarios where assumptions for the input data have to be made. Predictions and analogues, such as those presented in products in the Neftex portfolio, may be used for this process. Estimation of the volumes generated and those likely preserved enables the ranking of basins in terms of their petroleum potential. This increases understanding of the factors that affect the estimation of volume of hydrocarbons generated, and the associated risks. A crucial aspect of the workflow is the restoration of TOC and HI to original, pre- maturation values across the entirety of the source rock extent. This is a key value of the workflow and it is recommended that it be considered in any workflow requiring assessment of source rock hydrocarbon generative potential. Going forward, it is suggested that a simple workflow be defined to better predict the preservation and retention of hydrocarbons without the need to build a 3D basin model; particularly, in conventional systems where losses are generally large. The case study highlights that the estimated volumes carry a large degree of uncertainty; therefore, an error range on the data inputs should ACKNOWLEDGMENTS The author would like to thank Alex Bromhead, Christine Yallup, and Thomas Butt for their contribution in the development of the workflow, and Lawrie Cowliff and Daniel Slidel for their support and input into the project. REFERENCES Gaswirth, S.B. and K.R. Marra 2015. U.S. Geological Survey 2013 assessment of undiscovered resources in the Bakken and Three Forks Formations of the U.S. Williston Basin Province. AAPG Bulletin, v. 99, no. 4, p. 639-660. (XURBB_571096). Jin, H. and S.A. Sonnenberg 2013. Characterization for Source Rock Potential of the Bakken Shales in the Williston Basin, North Dakota and Montana. SPE Conference Paper, v. 1581243, p. 1-10. (XURBB_532277). Magoon, L.B. and W.G. Dow 1994. The Petroleum System- From Source to Trap. AAPG Memoir no. 60, American Association of Petroleum Geologists (AAPG), 1-655 p. (XURBB_460484). Roller, E. and A. Pepper 2018. Estimating the Ultimate Expellable Potential of Source Rocks: Defining “World Class” for Aquatic Organofacies with Examples from the Arabian, West Siberian, Bohai, and Williston Basins. AAPG Search and Discovery, v. 11055, p. 1-7. (XURBB_638403) Schmoker, J.W. 1994. Volumetric calculation of hydrocarbons generated. In L.B. Magoon and W.G. Dow (Eds.), The Petroleum System-From Source to Trap. AAPG Memoir no. 60, p. 323-326. (XURBB_614365). » More Literature On This Article AUTHORS Rachel Round — Senior Geochemist, Halliburton Landmark Rachel works on the Neftex Insights Petroleum Systems Analysis team as an organic geochemist and basin modeler. She has 10 years of industry experience, and prior to joining Neftex in 2014 she worked as an organic geochemist at APT (UK), and carried out internships at Fugro Robertsons and Getech. Rachel holds an MSc in Organic Geochemist from Newcastle University, and BSc in Geological Sciences from the University of Leeds. DISCLAIMER This article is a synthesis based upon published data and information, and derived knowledge created within Halliburton. Unless explicitly stated otherwise, no proprietary client data has been used in its preparation. If client data has been used, permission will have been obtained and is acknowledged. Reproduction of any copyrighted image is with the permission of the copyright holder and is acknowledged. 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