The synthesis process of the silicone ternary copolymer.

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The wettability of the formation is critical for the flow back of the fracturing fluid and can further affect the gas production. So it is very necessary to study the wettability of shale reservoir. Here, a novel fluorocarbon surfactant, N-ethyl-N-hydroxyethyl perfluorooctanoamide, was synthesized and characterized by different methods. the contact angles of water and n-decane on the shale increased from 36° and 0° to 121° and 105°, respectively, after treated by N-ethyl-N-hydroxyethyl perfluorooctanoamide (0.5 wt.%). The surface free energy reduced from 72 mN/m to 7.4 mN/m. The results agreed with that of imbibition and capillary tube rise test. Additionally, the analysis of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) showed that the roughness of shale surface remarkably increased. These results fully proved that the shale wettability is changed to super gas-wetting. Besides, the thermal analysis revealed that the novel fluorocarbon surfactant has good thermal stability. This indicates that it can be better applied to reservoir modifications at higher temperatures.

Summary Geopolymers have emerged as a promising alternative to Portland cement for oil and gas wells. Achieving effective zonal isolation by use of geopolymers may require controlling their expansion. This study investigates the effect of calcium oxide (CaO) as an expansive agent on the performance of geopolymer-based sealing materials. Specifically, we explore the impact of CaO reactivity on various material properties using isothermal calorimetry, Brunauer-Emmett-Teller (BET) surface area analysis, linear expansion (LE) test, shear bond strength, compressive strength, and hydraulic bond strength (HBS). Our results indicate that CaO reactivity is a critical factor affecting the properties and performance of geopolymers for zonal isolation. Lower reactivities are associated with longer induction periods and lower heat evolution, which in turn increase LE. While lower reactivity decreases compressive strength, it increases shear bond strength. However, the CaO with the lowest reactivity resulted in a very low HBS due to matrix cracking and leakage. Therefore, optimizing the reactivity of CaO expansive agents is essential to enhancing the properties of geopolymer-based sealing materials for oil and gas wells. Shown in this paper is the successful application of CaO as an expansive agent for granite-based geopolymers at shallow depths in oil and gas wells.