Alexandria Engineering Journal (Dec 2021)
A novel aluminum-based shale inhibitor and its wellbore stabilization effect
Abstract
To provide a better alternative to the current shale inhibitors, this paper designs a novel aluminum-based shale inhibitor by complexing aluminum with humic acid (HA), which is expected to enhance wellbore stability in drilling. Firstly, the alkali dissolution and acid precipitation (ADAP) method was chosen to extract HA from lignite from Shanxi and Yunnan, China. Next, the complexation conditions for aluminum-humic acid (Al-HA) were optimized through orthogonal tests, including reaction ratio, temperature, time, and pH. The best complexation conditions for Al-HA-1 were determined as pH = 5.0, HA/NaAlO2 = 7/3, T = 75℃, time = 30 min, and those for Al-HA-2 as pH = 10.0, HA/ NaAlO2 = 3/7, T = 65℃, and time = 30 min. Further, several tests were conducted to evaluate the inhibition performance of our inhibitors. The results show that the hot rolling recovery of shale sample in 1.2 wt% Al-HA-2 solution was up to 90.52% after hot rolling for 16 h at 120℃; the linear swelling rate of artificial bentonite core in 1.2 wt% Al-HA-2 solution was merely 20.38% after 16 h. The inhibition mechanism of Al-HA mainly consists of flocculation on shale surface and chemical reverse osmosis. Both phenomena suppress filtrate intrusion and reduce pore pressure transmission. These superior properties make the proposed inhibitors a promising choice for wellbore stabilization, especially in shale oil/gas formations.
