# Effect of Aging on Class G High Sulfate-Resistant Oil Well Cement Under High Relative Air Humidity
## 1 Introduction  
Cement is an important aspect of oil and gas reservoir development that serves to protect and secure the casings of oil and gas wells. As the demand for oil and gas resources continues to increase, offshore oil fields have garnered increasing attention [1]. The uptakes of water vapor (H\({}_{2}\)O) and carbon dioxide (CO\({}_{2}\)) from the atmosphere by oil well cement resulting a slight hydration, which is referred as the aging of oil well cement. After leaving the cement factory, fresh cement ages to varying degrees with respect to the relative air humidity and aging time. The aging of cement during transportation and storage has a significant effect on its properties. Owing to transportation challenges and negative weather conditions, bulk oil well cement is occasionally stored long-term, sometimes for tens of days, in high-humidity warehouses along the coast. In particular, in the summer and autumn, the air humidity in a warehouse exceeds 80% RH. Long-term storage in a high-humidity environment can cause changes in cement properties, which leads to the need to adjust the cement paste formulation. Cement aging has negative effects on cementing process. Consequently, it is important to study the aging mechanism of oil well cement. According to previous studies [2,3], different mineral compositions in cement sorb water at varying relative humidities. The relative humidity thresholds for each mineral composition, ranked from low to high, are as follows: hemihydrate gypsum at 34% RH, orthogonal C\({}_{3}\)A at 55% RH, C\({}_{3}\)S at 63% RH, C\({}_{2}\)S at 64% RH, C\({}_{4}\)AF at 78% RH, and cubic C\({}_{3}\)A at 80% RH [4]. When oil well cement was stored in high humidity areas such as coastal areas, the relative air humidity was usually greater than 80% RH [5]. This meant that almost all of the major clinker phases and gypsum in the cement began to sorb water, and the aging of the cement had a greater impact on its performance [6]. In view of the effect of aging on cement properties, some previous scholars have carried out studies on it. [PERSON] [7] reported that acicular ettrinigite is the main product of cement aging at 90% RH. The excessive growth of ettrinigite on the clinker surface hinders the entry of water into the unreacted portions of the clinker [8], thus reducing the early hydration heat. After 14 d aging, the compressive strength of the hardened cement pastes at 7 d of age was less than 3 MPa. [PERSON] [9] reported that, during cement aging, the formation of ettrinigite and agglomeration of cement particles caused by water absorption are two antagonistic processes. They further suggested that the overall content of C\({}_{3}\)A, particularly the content of orthogonal C\({}_{3}\)A, along with the aging time, significantly affects the performance of the cement [10,11]. Both studies suggested that the formation of AFt during aging affected the performance of cement. [PERSON]'s [12] experiments revealed that the hydration heat release peak of cement delayed with increasing aging time. They proposed that C\({}_{3}\)S exposed to air generated a thin layer of C-S-H on its surface, which acted as a barrier when mixed with water and hindered its hydration [13]. The results revealed that the hydrations of C\({}_{3}\)A and C\({}_{3}\)S, which are more sensitive to water, and their hydration products led to changes in the cement properties during the aging process. [PERSON] [14] also reported that the reduction in the early compressive strength of aged cement was linearly correlated with the decrease in the accumulated heat release from the early hydration of cement. They posited that the formation of hydration products during the aging process hindered the reaction between the cement and water. These authors suggested that adding fine lime powder to the cement, which serves as an additional nucleation site for hydration, could mitigate the effect of aging [15,16].