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Second, when the return height of cement slurry is 0 m, eight different setting times, 0.5 days, 1 days, 2 days, 3 days, 5 days, 7 days, 14 days, and 28 days, were selected to test the ultimate bearing capacity.Īt present, there is no definite standard or specification for the determination of the ultimate bearing capacity of the conductor. Other values mean that the cement slurry returns to a height below the mud surface. The returned height of 0 m indicates that the cement slurry returns to the mud surface height. Therefore, seven different return heights of cement sheath, 0 m, -1 m, -1.5 m, -2 m, -2.5 m, -3 m, and -3.5 m, were selected as test variables. Finally, the accuracy of the calculation model of the ultimate bearing capacity was verified by simulation experiments and the influence of the setting time on the ultimate bearing capacity was explored.Īccording to ( 9), the return height of the cement slurry is the key factor for the ultimate bearing capacity of the conductor.

A calculation model of the ultimate bearing capacity of the conductor considering the return height of the cement sheath was established. Besides, the influence of hole enlargement on bearing capacity was considered during running the conductor drilling. Therefore, for the operating characteristics of running the conductor by offshore drilling, the axial load distribution characteristics and bearing capacity mechanism of the conductor were first analyzed in this paper from the perspective of operation characteristics of the drilling method. As a result, the actual bearing capacity of the conductor cannot be accurately predicted. In real operation, on the premise that the design value of the bearing capacity of the conductor meets the wellhead stability requirements, the sinking of the conductor still occurs, which proves that the factors affecting the actual bearing capacity of the conductor have not yet been fully grasped. Nevertheless, these studies did not focus on the conductor and did not specifically analyze the influence of cement sheath height on the mechanical behavior of the conductor from the perspective of offshore drilling. Gouvenot calculated the bearing capacity of cemented piles in a marine environment. Olson and KARLSRUD K theoretically analyzed the axial bearing capacity of steel piles in sand and clay. Therefore, the study on the influence of cement slurry return height and the setting time on the ultimate bearing capacity of the conductor is of great significance to the construction of shallow water exploration well. The insufficient return height of cement slurry causes complicated accidents such as more serious offshore wellhead sinking and even instability. The bearing capacity provided by the conductor is closely correlated to the height of the cement sheath and the cementing strength of the cement slurry. However, cement slurry often cannot return to the designed height in real operation due to the difficulty in estimating the amount of lost circulation and cement slurry in the shallow seabed.

The cement slurry is consolidated into cement sheath to bond the soil with the conductor to provide lateral friction for the pipe string. The conductor is put into the wellbore and the annulus is filled between the conductor and the wellbore with cement slurry. The general step of the drilling method is to drill a wellbore larger than the diameter of the conductor with a bit. The drilling method is one of the main methods of running the conductor in shallow-water drilling and has the advantages of strong adaptability to the shallow seabed soil and great bearing capacity. It was concluded that the friction between the cement sheath and the soil layer is the key factor that decides the main bearing capacity of the conductor. In addition, the law of the influence of the return height of cement slurry on the ultimate bearing capacity of conductor and the strength difference of the two cementing surfaces between conductor and cement ring and between the cement sheath and submarine soil layer and its changing rules with time were explored and studied by field experiment. Second, a calculation model of axial bearing capacity of the conductor with the size of the conductor and the return height of cement slurry as variables was established on the basis of the hole enlargement that often occurs during drilling.

For the influence of the insufficient return height of cement slurry on the mechanical behavior of the conductor after running the conductor by shallow water exploration well drilling, the axial load distribution characteristics and bearing capacity mechanism of conductor were first analyzed from the perspective of operation characteristics of the drilling method. The height of the cementing cement sheath of the conductor for offshore drilling is the key factor affecting wellhead stability.