A revolutionary new core analysis method for unconventional hydrocarbon reservoirs based on rate-transient analysis theory

Significance 

Recent technological advancements, such as the use of horizontal wells combined with hydraulic fracturing, has led to economic development of ultra-low permeability (unconventional) hydrocarbon reservoirs. Optimization of unconventional reservoir development using horizontal wells, however, requires quantification of critical reservoir properties affecting the flow of hydrocarbons to the well, such as permeability and porosity. There are a variety of laboratory-based (rock) core analysis techniques that have been developed specifically for unconventional reservoirs, each with their own advantages and limitations. However, none of these techniques properly reproduce the conditions under which horizontal wells produce in the field.

Hydraulically-fractured horizontal wells producing from unconventional reservoirs initiate a pressure transient that propagates out into the reservoir from the hydraulic fracture over time, like waves emanating from a rock thrown into a pond”, says Dr. Christopher R. Clarkson from the University of Calgary. The production data from a well during this transient flow period can be analyzed using an engineering method called rate-transient analysis (RTA) to extract key information, such as hydraulic fracture properties. Models used for RTA, however, commonly require estimates of reservoir permeability and porosity, often determined in the laboratory.

“Our goal is to simulate in the laboratory how a well produces in the field, and apply the same RTA models to core tests. This allows for a more realistic and representative analysis.” Clarkson demonstrated several years ago (Clarkson et al., 2012; Clarkson and Qanbari, 2013) that this was theoretically possible using reservoir simulation, but the method was not tried in the laboratory until now.

With the aid of his laboratory team, consisting of Ms. Atena Vahedian, Dr. Amin Ghanizadeh, and Mr. Chengyao (Charles) Song, a new experimental apparatus was constructed and procedure developed. A proof-of-concept of the RTA core analysis method, using this new equipment and procedure, was published in the research journal, Fuel (Clarkson et al., 2019).

In brief, using a low-permeability sample from Western Canada, methane gas was first injected into the core plug and allowed to stabilize. The gas was then allowed to produce from one end of the sample at approximately constant flowing pressure, and the gas rate produced over time measured. The gas rates were then analyzed using RTA techniques and models, analogously to what is done with well production data in the field.

“The results, while predicted using simulation several years ago, were better than expected, thanks to my research team”, remarks Clarkson. The proof-of-concept test demonstrated the following advantages of the new method: 1) the same flow regimes (patterns of flow during production) observed with field data were observed during the core test; 2) two permeability estimates and a pore volume (and hence porosity) were obtained from RTA of the data, providing an important redundancy for permeability estimation not typically available with other techniques; 3) the permeability and porosity estimates, later measured as a function of pore pressure and effective stress, were repeatable and consistent with independent methods; and, 4) the results were obtained in a fraction (e.g. 10%) of the time of routine unsteady-state core analysis techniques, such as pulse-decay.

In summary, Professor Christopher R. Clarkson and his research team successfully developed a novel core analysis technique that effectively reproduces the conditions that wells experience in the field and can be analyzed using the same methods. Altogether, the University of Calgary study will advance laboratory-based methods for permeability and porosity estimation in unconventional hydrocarbon reservoirs.

A revolutionary new core analysis method for unconventional hydrocarbon reservoirs based on rate-transient analysis theory - Advances in Engineering A revolutionary new core analysis method for unconventional hydrocarbon reservoirs based on rate-transient analysis theory - Advances in Engineering

About the author

Amin Ghanizadeh is a Petrophysical Research Supervisor and Laboratory Manager at the Tight Oil Consortium at the Department of Geoscience at the University of Calgary. With a M.Sc. in Chemical Engineering (University of Tehran, Iran; CSIRO energy Technology, Australia) and a PhD in Petroleum Geoscience (RATH Aachen University, Germany), during the past +10 years, Amin has been intensively involved in industry/government-sponsored projects in Iran, Australia, Germany and Canada investigating fluid storage and transport processes in synthetic carbonaceous materials (carbon nanotubes, activated carbons) and low-permeability geological media (coals, tight sandstones, shales/mudrocks). Arranged chronologically, these national/international projects include the Australian CO2CRC Project (www.co2crc.com.au), German CO2Seals Project, European GASH Project (www.gas-shales.org), and most recently, Canadian Tight Oil Projects (www.tightoilconsortium.com). Amin’s current research interests are focused on 1) advancing core and cuttings analysis for improved characterization of geochemical, petrophysical and geomechanical properties and fluid-rock interaction in unconventional light oil reservoirs and 2) investigation of Improved Oil Recovery (IOR) in unconventional light oil reservoirs.

Among more than 60 peer-reviewed technical articles and conference contributions, Amin is the co-author of three invited review articles that discuss a variety of field- and laboratory-scales processes governing hydrocarbon storage and transport in unconventional oil/gas resources. Amin is further the recipient of “2018 Award of Excellence: Research Staff” at the Department of Geoscience at the University of Calgary.

About the author

Atena Vahedian is a petrophysical assistant at the Tight Oil Consortium at the Department of Geoscience at the University of Calgary with a B.Sc. in Petroleum Engineering (Petroleum University of Technology, Ahvaz, Iran) and is studying MEng. in Petroleum Engineering at the University of Calgary, Calgary, Canada.

Her research focus is on petrophysical characterization of tight reservoirs using various experimental instruments such as Pulse Decay Permeameter, Shale Matrix Permeameter, 3Flex surface analyzer, and pycnometer. In addition, Atena has been working on developing new experimental setups for permeability estimation of core plugs from tight formations and has co-authored/authored more than 20 conference and journal papers.

About the author

Christopher R. Clarkson is a professor and the Shell/Encana Chair in Unconventional Gas and Light Oil research in the Department of Geoscience and an adjunct professor with the Department of Chemical and Petroleum Engineering at the University of Calgary. His work focus in industry was on exploration for and development of unconventional gas (UG) and light oil (ULO) reservoirs.

His research focus since coming to U of Calgary in 2009 has been on advanced reservoir characterization methods for UG-ULO, such as rate- and pressure-transient analysis, flowback analysis, and core analysis. He is also interested in simulation of enhanced recovery processes in UG-ULO, and how these processes can be used to reduce greenhouse gas emissions. Clarkson leads an industry-sponsored consortium called “Tight Oil Consortium”, focused on these research topics for unconventional light oil reservoirs in Western Canada.

Clarkson holds a Ph.D. degree in geological engineering from the U. of British Columbia, Canada, and is the author of numerous articles in peer-reviewed scientific and engineering journals. Clarkson was an SPE Distinguished Lecturer for the 2009/2010 lecture season, is the 2016 recipient of the SPE Reservoir Description and Dynamics Award (Canadian Region), and the 2018 recipient of the SPE Calgary Sections’ Technical Excellence and Achievement Award. He also received the 2017 ASTech award for “Outstanding Achievement in Applied Technology and Innovation” for his work on rate-transient analysis of unconventional reservoirs.

References

Clarkson, C., Vahedian, A., Ghanizadeh, A., & Song, C. (2019). A new low-permeability reservoir core analysis method based on rate-transient analysis theory. Fuel, 235, 1530-1543

Go To Fuel

Clarkson, C.R., Nobakht, M., Kaviani, D. and Kantzas, A., 2012. Use of pressure- and rate-transient techniques for analyzing core permeability tests for unconventional reservoirs. Paper SPE 154815 presented at the SPE Americas Unconventional Resources Conference held in Pittsburgh, Pennsylvania, 5-7 June.

Clarkson, C.R., and Qanbari, F., 2013. Use of pressure- and rate-transient techniques for analyzing core permeability tests for unconventional reservoirs: Part 2. Paper SPE 167167 presented at the SPE Unconventional Resources Conference-Canada held in Calgary, Alberta, 5-7 November.

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