Element release and reaction-induced porosity alteration during shale-hydraulic fracturing fluid interactions

Geochemical conditions conducive for retention of trace elements and radionuclides during shale–fluid interactions

“…Based on the previous studies monitoring pH of the unbuffered solution in contact with Marcellus shale, the pH of leachates dris approximately by $2 units from the initial solution pH due to the interplay between the acid generating component (pyrite dissolution) and acid buffering component (calcite dissolution). 16,20 The change in solution pH reported in previous studies is not sufficient to destroy the buffering capacity of the leaching uids associated with our treatments. Therefore, we choose to not measure the nal pH of the solution.…”

“…Previous studies have identied iron-bearing minerals as a major source of trace metals. 16,31 Therefore, we plotted correlation plots of Fe with other elements to identify which elements were associated with iron solids. The elements which were positively associated with Fe are Cu (r ¼ 0.687), Ni (r ¼ 0.738), Mn (r ¼ 0.847), Cr (r ¼ 0.716), PbAs (r ¼ 0.734), and S (r ¼ 0.687) and their correlation plots with Fe are shown in Fig.…”

“…Harrison et al reported that shale with low carbonate and high pyrite composition resulted in porewater acidication and thereby increasing the release of major elements and U, Pb, and Ni from shale to porewater. 16 In addition to pH, various other solution chemistry parameters could affect the release of trace elements from shale. Wang et al reported the inuence of oxidant concentration, solid : water ratio and pH on the mobility of major elements from Eagle Ford and Bakken shale.…”

Geological characteristics of shale in the Silurian (Sichuan) basin and chemical reaction of its reservoir under the action of fracturing fluid

“…At present, in shale gas exploitation in China and abroad, the flowback rate of fracturing fluid is relatively low (Yan et al 2015), and about 10-30% fracturing fluid returns to the ground (Tikhomirova et al 2011). In addition to affecting the shale gas exploitation effect, the remaining fracturing fluid may also contain a large number of salts (Cl, Br) which will promote the dissolution of carbonate minerals (Joewong et al 2015) and metal pollutant (Countess et al 2014) and heavy metal pollutant (Dustin et al 2018) which will change the permeability of rock (Harrison et al 2017). Fletcher (2012) pointed out that the overflow of fracturing fluid brought large pollution risk to the underground water resource of Pennsylvania.…”

Experimental evaluation of ASP flooding to improve oil recovery in heterogeneous reservoirs by layered injection approach

“…Although the above method can effectively improve the oil recovery of low‐permeability oil layers, there are still many deficiencies. For hydraulic fracturing technology, only a small part of the injected fracturing fluid can be recovered, and most of the injected fracturing fluid remains in the formation, 29,30 and the remaining fracturing fluid plugs the original connected pores and throats, resulting in a decrease in physical permeability 31 . In addition, the residual fracturing fluid may form two‐phase seepage resistance and reduce the effective permeability of the oil phase 32 ; for CO 2 flooding, CO 2 injection may bypass the remaining oil zone and tend to flow through fractures, resulting in low sweep efficiency 33‐35 ; for profile control, the injected gel permanently blocks the high‐permeability layer 36 .…”