## 1 Introduction  
The primary purpose of cementing is to inject a cement slurry system into the annulus between the casing and formation, to form a good isolation barrier and prevent oil, gas and water channeling. Generally, low-temperature cementing refers to cementing operations with cement slurry circulation temperature below 45 \({}^{\circ}\)C [1]. Cementing operation in a special environment, such as a deep-water shallow layer, and the low temperature at the bottom of the well have an impact on the performance of cement slurry [2, 3]. Low temperature will significantly reduce the cement hydration rate, resulting in longer thickening time of cement slurry, slower development of compressive strength, insufficient shear stress to support casing and prolonged waiting time, which will increase the construction cost of the oil and gas well [4, 5, 6]. Therefore, to improve the early strength development and the low-temperature cementing quality of cement slurry, it is necessary to study the admixtures that enhance the mechanical properties of cement under low temperature. An early-strength agent is one of the critical admixtures to improve the early strength of oil well cement-based composites at low temperature. It is divided into chloride salts, sulfates and organic substances [7; 8; 9]. The chloride salt early-strength agents are widely used because of their low cost and good early-strength effect. The mechanism is the addition of a chloride salt early-strength agent, which reacts with tricalcium aluminate in inorganic cementitious materials to produce insoluble chloro-aluminate hydrate. Chloride is easy to dissolve and accelerates the hydration and hardening of the cement. [PERSON] et al. [10] studied the effect of NaCl and KCl on the cement, and the hydration rate increased linearly with the logarithm of the concentration of chloride ions. [PERSON] et al. [5] studied the acceleration performance and mechanism of chlorides on oil well cement at low temperatures. The essence of sodium sulfate early-strength agents is a strong electrolyte, which can increase the ionic strength of cement and has certain compressibility for the diffusion of the double electric layer. In the process of cement hydration, sodium sulfate reacts with free calcium hydroxide to improve the pH value of the solution and provide an environment for calcium sulfoaluminate hydrates to accelerate the hardening of oil well cement-based composites [11]. The organic early-strength agents are mainly divided into low-grade organic acid salts and alcohol amines, of which the most commonly used are triethanolamine and calcium formate. [PERSON] et al. [12] proposed that triethanolamine (TEA) can regulate the initial setting time. [PERSON] et al. [13] suggested that TEA can accelerate the hydration process of C\({}_{3}\)A and delay the hydration process of C\({}_{3}\)S. Triethanolamine has an emulsifying effect. It is readily adsorbed on the surface of cement particles when mixed into cementitious materials and to forms a charged hydrophilic film which hinders the accumulation of cement particles and produces a suspension stabilization effect. The surface tension is reduced to a certain extent so that the cement particles are fully contacted with water, and the hydrolysis of the cementitious material is promoted. In addition, the structure of triethanolamine determines that it is easy to complex with metal ions in cement to form a stable complex, which accelerates the hydration of tricalcium aluminate and improves the early strength of cement. Calcium formate is weakly acidic in water, which can promote the hydration of tricalcium silicate to a certain extent, reducing the time required for cement to harden. These early-strength agents have a certain effect on improving the early compressive strength of cement stone. However, some studies have shown that chloride salt early-strength agents will increase the yield value of cement slurry, increase permeability and reduce sulfate corrosion resistance [14].