ABSTRACT

Due to the effect of alternating impact load of pile hammer, the overall stability and safety control of conductor in the process of pile driving is a key problem to be solved in site construction. Based on the actual driving conditions of a well, the mechanical properties of the whole pipe during operation are analyzed by using ABAQUS finite element software. The factors affecting the stability of conductor during pile driving were analyzed, including length of free section, number of hammering and hammering frequency. The results show that for the 30in(762mm) diameter conductor, the maximum free section length meeting the stability requirement of pile driving operation is 45m. The maximum surface stress always occurs in the middle of the maximum free section during the hammering process. When the hammer load is applied, greater stress response will be generated on the surface of the conductor. In the initial stage of pile driving, the surface stress of conductor is positively correlated with the hammer frequency. The greater the hammer frequency is, the greater the surface stress is. As the pile driving process continues, the low frequency hammering operation will produce greater stress fluctuations on the conductor surface.

INTRODUCTION

In the process of shallow water oil and gas development, conductor is the first layer pipe body of wellbore construction. The conductor is inserted into the shallow soil of the seabed to a certain depth from the wellhead of the offshore platform. It plays an important role in isolating seawater, supporting wellhead equipment, building safe circulation channels, resisting environmental loads and so on. There are mature methods for calculating the ultimate bearing capacity and mud penetration depth of conductor. The calculation method of the API specification is widely recognized by the engineering community(API,2011). Liu Qingyou et al.(2019) established a mechanical model of conductor considering the characteristics of submarine strata, axial and lateral loads. The factors affecting transverse displacement and stress distribution of conductor during oil production are analyzed. Based on the theoretical analysis of rock and soil mechanics, Yang Jin et al.(2002,2003) proposed a model for calculating the ultimate bearing capacity of conductor under different seabed soil layers and predicting the depth of mud penetration.

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