Preparation and performance of ammonium-malic salts as shale swelling inhibitor and a mechanism study

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Abstract
A series of ammonium-malic salts (AMS) was prepared with malic acid and amines as small molecular shale swelling inhibitor. The inhibitors were screened by the linear expansion test of bentonite firstly, and the result shows that the inhibitor prepared by malic acid and tetraethylenepentamine with the mole ratio of 1:3 (AMS-9) displays excellent inhibition on the hydration expansion of bentonite. The results show that AMS-9 has superior performance to inhibit the hydration swelling and dispersion of bentonite, and the swelling rate of 0.5% AMS-9 reaches down to 57.14%. Then the efficiency AMS-9 in water based drilling fluid was investigated, which shows AMS-9 is compatible with the conventional additive, modified starch and PAM. Besides the inhibition mechanism of the AMS was discussed using FT-IR and cation exchange. The inhibition mechanism of AMS-9 to bentonite should be due to the ion exchange of ammonium and the Ca2+, hydrogen bonding and surface modification.

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