1. Fracturing flowback fluids from shale gas wells in western chongqing: Geochemical analyses and relevance for exploration & development.
- Author
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Fu, Yonghong, Jiang, Yuqiang, Hu, Qinhong, Luo, Tongtong, Li, Yaogan, Lei Zhian, Wang, Zhanlei, and Yin, Xingping
- Subjects
SHALE gas ,GAS wells ,FRACTURING fluids ,ALKALINE earth metals ,OIL shales ,ANALYTICAL geochemistry ,WATER-rock interaction - Abstract
Understanding the behavior and composition of fracturing flowback water (FFW) can provide insight into in situ water–rock interactions, assessment of the success of the fracturing operations. FFW was collected from three wells (Z202-H1, Z203, and Z205) for up to 108 days after fracturing in the same area of western Chongqing, China. The samples were analyzed for the concentrations of various ions (Na
+ , K+ , Ca2+ , Mg2+ , Ba2+ , Sr2+ , Cl− , SO 42− , Br− , HCO 3− , etc.) and for the stable isotope composition (δ D and δ18 O) of water. With increasing flowback time, the ionic concentration and total salinity increased (e.g., from 315 mg/L to 37117 mg/L after 38 days for well Z203), stable isotopic ratios became heavier (e.g., δD values changed from −23.59‰ to −14.32‰, δ18 O values changed from −3.91‰ to −1.92‰). The total salinity of the FFW is shown to be the result of mixing of the highly saline formation water and the low-salinity fracturing water. FFW from Z205 had higher concentrations of Li+ and NO 3− , heavier stable isotope compositions, larger Na+ /Cl− ratio, smaller (Cl− -Na+ )/Mg2+ ratio, and larger SO 42− × 100/Cl− ratio compared to the other two wells. All these phenomena revealed that Z205 is more likely to contact with active aquifers which is not conducive to natural gas preservation, because Z205 is close to (less 300 m from) a grade II fault. The RITS and RSIH with flowback time in Z203 were higher than Z202-H1, which shows that FFW from Z203 contained a greater fraction of formation water released from pores or fractures due to complex the network fractures formed by fracturing. Therefore, the fracturing operations of Z203 is better than Z202-H1. This result can reveal the reason for the production difference of adjacent wells, which is difficult to explain by similar total SRV. • The FFW is a mix of injected water and formation water mainly related to fractures. • The difference of trace elements concentration and ionic ratio can reflect preservation conditions of shale gas. • Lager RITS and RSIH values can reveal better fracturing operations.. [ABSTRACT FROM AUTHOR]- Published
- 2021
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