The three papers in this issue cover a diverse set of relevant technical challenges important to the oil and gas industry. The first two deal with bitumen, and the last one with unconventional gas. The first paper explores the possibility of in-situ upgrading of bitumen using combustion-tube tests. The second measures evaporative behaviour of diluted bitumen (dilbit) to help with design of the recovery effort, in the event of a pipeline spill. The last paper provides new insights into transient analysis of shale gas by including effects of rejuvenated natural fractures.
The first paper, Upgrading of Athabasca Bitumen Using Supported Catalyst in Conjunction With In-Situ Combustion, addresses the holy grail of in-situ upgrading. It explores the use of in-situ combustion with hydroprocessing catalyst to produce upgraded oil. This work was completed by University of Calgary’s In Situ Combustion Research Group (ISCRG) and led by Professors Gord Moore and Raj Mehta. Upgrading is demonstrated clearly in the 1D combustion-tube tests. For wet combustion, upgrading was obtained without any preheat of the catalyst, indicating that wet combustion may be preferred for field application of this technology. An intermediate step could be to perform 2D cross-sectional experiments to better understand fluid (air/water) movement in the reservoir in presence of gravity. As the authors note, the next challenge is to develop a mobile nanocatalyst, which can mimic the reactivity and can be placed in the steambank region, ahead of the combustion zone.
The second paper addresses an important issue of how dilbit behaves in the event of a spill during pipeline transportation. In particular, the paper investigates evaporative weathering behaviour of dilbit in freshwater environment. Evaporative Weathering of Diluted Bitumen Films provides measured laboratory data to improve our understanding of parameters that affect dilbit evaporation behaviour. It demonstrates that in absence of sediments, before significant photo-oxidation, and in modest ambient temperature, dilbit should stay afloat on freshwater for at least 10 days (duration of the study). This data will be useful in the design of post-spill activities.
Unlike the first two papers, which present data from laboratory measurements, results on the basis of extensive numerical modelling are presented in Pressure-Transient Characteristics of Hydraulically Fractured Horizontal Wells in Shale-Gas Reservoirs With Natural- and Rejuvenated-Fracture Networks. The paper covers an important topical issue of pressure transient analysis and productivity of tight gas reservoirs. It provides new insights into transient characteristics of a hydraulically fractured horizontal well in a shale-gas system by including effects of rejuvenated fractures. The paper shows that the boundary induced by the rejuvenated fractures generates a pseudoboundary-dominated flow. A type-curve matching, which could provide the possibility of predicting reservoir properties, is included.
Mridul Kumar, Issue Coordinator
Mridul Kumar is a Chevron Fellow, Principal Advisor, and Unit Manager for Reservoir Performance Products at Chevron Energy Technology Company. He is also a member of Chevron’s reserves advisory committee. Kumar has been with Chevron for 33 years, and is currently responsible for research, development, deployment, and support of Chevron’s reservoir-engineering tools, workflows, and technologies worldwide. Earlier, he was Team Leader of the Heavy Oil and Unconventional Reservoirs team, providing technical leadership for research, development, and application of technologies to Chevron’s global heavy-oil operations, and contributed to the success of Chevron’s key heavy-oil and thermal-recovery projects.
Kumar holds a B.Tech. degree (with distinction) from the Indian Institute of Technology Kanpur, and MS and PhD degrees from the Pennsylvania State University, all in mechanical engineering.
He is a SPE Distinguished Member and has been a SPE Distinguished Lecturer. Kumar has cochaired SPE forums, applied technology workshops and symposia, and has been on the World Heavy Oil Congress program committee since its inception. He coauthored the SPE Reprint volume 61 on Heavy Oil Recovery. He received the 2002 SPE Western Region Technical Achievement Award, and was president of the SPE Golden Gate Section through 2001 – 2002. Kumar has coauthored over 50 papers and four patents, and has presented invited seminars worldwide.
In-Situ Combustion and Upgrading
Upgrading of Athabasca Bitumen Using Supported Catalyst in Conjunction With In-Situ Combustion discusses the successful use of the steambank moving ahead of the combustion zone for in-situ heating of the supported catalyst bed. Instead of using external heaters to heat the catalyst bed, in-situ-generated steam provided sufficient high temperature to activate the catalyst for upgrading of Athabasca bitumen. This system will reduce the cost and accessibility problems associated with the external heating of the catalyst bed during in-situ upgrading over supported catalyst. Description of the two processes, one involving the use of external heating and the other involving the use of steam, is highlighted. A summary of the analysis of the produced oil obtained from the two processes are comparatively presented.
Evaporation of Diluted Bitumen
Evaporative Weathering of Diluted Bitumen Films presents data on the evaporation rate of diluted bitumen films and Alberta Sweet Blend (ASB) films on glass and on water at temperatures from 5 to 25°C and at several air-flow rates. The change in density and viscosity with evaporation is reported for both films. The behaviour of the diluted bitumen and ASB films are compared and the different mechanisms controlling mass transfer from each film are discussed. The effect of water on the films and the likelihood of diluted bitumen films sinking in water after prolonged weather are evaluated. The potential to extend the results of this study to oil spills in general are discussed.
Tight Gas Reservoirs
Pressure-Transient Characteristics of Hydraulically Fractured Horizontal Wells in Shale-Gas Reservoirs With Natural- and Rejuvenated-Fracture Networks discusses the effects of rejuvenated fractures, which are revitalized natural fractures created by hydraulic fracturing. Proposed model considering rejuvenated fractures is used to analyze the pressure-transient characteristic and productivity in shale-gas reservoirs. Results are compared with the existing model, not considering rejuvenated fractures, and parametric studies are conducted with respect to reservoir and fracture properties. The proposed model shows the pseudoboundary-dominated flow induced by the rejuvenated fracture. Reservoir properties are calculated with the generated type curves and Barnett shale data is used to verify the proposed model with pressure responses.