Understanding the Origin of Flowback Salts: A Laboratory and Field Study
- Ashkan Zolfaghari Sharak (University of Alberta) | Mike Noel (University of Alberta) | Hassan Dehghanpour (University of Alberta) | Doug Bearinger (Nexen Energy ULC.)
- Document ID
- Society of Petroleum Engineers
- SPE/CSUR Unconventional Resources Conference – Canada, 30 September–2 October, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2014. Society of Petroleum Engineers
- Reservoir Characterization, Fracture Network, Salt Origin, Flowback Process
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Several past studies have focused on the saline flowback water to evaluate the hydraulic fracturing operations. The origin of the salts in the flowback water is important for the assessment of the flowback process. In this study, laboratory and field analyses are performed to provide a better understanding about the origin of the flowback salts.
The field study analyzes the total salt concentration (salinity) and ion concentration data measured during the flowback process for the Muskwa (Mu), Otter-Park (OP), and Evie (Ev) formations. The concentration profiles of both the barium and chloride during the flowback process, whereas the iron concentration declines after experiencing an initial increase.
The laboratory study encompasses contact angle, XRD, imbibition, individual ion concentration, surface element, and adsorption isotherm experiments for samples from the OP and Ev formations. To investigate the effects of fluid-rock interface area on the liquid uptake and diffusion rate of individual ions, a series of imbibition experiments are carried out for different values of surface to volume ratios (specific surface or “Asp”). The electrical conductivity and individual ion concentrations are measured during the imbibition process. XRD data is analyzed to determine the mineralogy of the samples. SEM-EDX analysis is performed to determine the distribution of the elements on fresh break and natural fracture surfaces of the samples (in addition to a sample from the Lower Keg (LK) formation). Finally, since both ion transfer and water adsorption processes occur during the imbibition experiment, an adsorption isotherm experiment is carried out to prevent the ion transfer into/out of the rock in order to solely study the water adsorption process. The laboratory results show that barium is mainly concentrated in the natural fractures; and therefore the shape of the barium concentration profile in the flowback water maybe an indication of the complexity of the fracture network.
Unconventional shale gas is emerging as an important source of energy suply in United States and Canada (Frantz and Jochen; 2005). Sustaining a continuous growth in the energy market, shale gas is expanding its share of the global natural gas supply by 6.5% per annum, providing nearly half of the world’s natural gas growth (Energy outlook 2035, 2014). In absolute terms, shale gas expands by 50 Bcf/d. Between 2012 and 2035, shale gas is expected to cause the US gas production to rise by 45% (Energy outlook 2035, 2014). Unconventional shale gas production is rapidly emerging as a vital source of natural gas, and the application of multi-lateral horizontal drilling and multi-stage hydraulic fracturing technologies is paving the way to economical exploitation of these shale resources.
In hydraulic fracturing, a large volume of fracturing fluid (mainly water) is injected into the reservoir to create multiple fractures and increase reservoir contact per well (Cheng, 2012). Then, the wells are usually shut-in for a period of time (also known as the soaking period) to increase hydrocarbon production (King, 2012; Lan et al., 2014). During production, a portion of the injected fracturing fluid returns to the surface alongside the produced hydrocarbons (Abbasi et al., 2012). This returning water is called flowback water.
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