Modeling of Local and Macroscopic In-Situ Stresses of Salt Layer in the Tarim Basin

Abstract

ABSTRACT: The in-situ stresses of the Kumgrem salt layer in the Tarim Basin is not clear. Since its development, there have been several stuck-bit accidents, affecting oil and gas drilling and development. Therefore, it is significant to establish the in-situ stresses field analysis model to define the in-situ stresses characteristics of the Kumgrem salt layer in the Tarim Basin. In this paper, the in-situ stresses of the Kumgrem salt layer in the Tarim Basin is modeled from local and macroscopic scales. A local in-situ stresses analysis model is established based on logging data. On this basis, a macroscopic in-situ stresses analysis model considering geological structure is established using the finite element method based on seismic section. The predicted results of the local and macroscopic in-situ stresses analysis model are in agreement with the actual situation. This study can guide the drilling and completion design in salt rock formations. 1. INTRODUCTION Salt layers are often encountered in both onshore and offshore oil and gas drilling. In the process of salt layers drilling, the complicated mechanical properties of salt layers lead to bit stuck, casing stuck, casing failure, and other accidents (Al-Saeedi et al., 2011, Liu et al., 2021, Chengxin et al., 2023). Serious stuck-bit accidents have occurred in many Wells in the salt layer of Kumgrem Formation in Tarim Basin, China, resulting in frequent side drilling, which seriously restricts the safe and efficient exploitation of oil and gas resources. It is of great significance to clarify the distribution of in-situ stresses in the salt rock. Many previous studies have been conducted on in-situ stress. The relative magnitude of in-situ stresses can be judged according to the characteristics of geological structures (Yongmeng, 2016, Zheng et al., 2016). The vertical principal stress is maximum in the normal fault control region, minimum in the reverse fault control region, and between the horizontal maximum and minimum principal stress in the strike-slip fault control region. This kind of in-situ stresses judgment method can only get the relative magnitude of in-situ stresses, and cannot quantitatively analyze the magnitude and direction of in-situ stresses. some studies have proved that rocks have a significant Kaiser effect through a large number of experiments (Godman, 1963, Tensi,2004), and then derived the method of measuring in-situ stresses by using the Kaiser effect. However, this method can only test the state of in-situ stresses at a single point, and the dispersion of the results is high. At the drilling site, the most commonly used in-situ stresses measurement methods are direct measurement methods such as formation loss test and hydraulic cracking method (Zhang et al., 2014). The direct measurement method can obtain the in-situ stresses of the formation in real-time, but it can still only obtain the single-point in-situ stresses. The method of post-drilling analysis using logging data can obtain the variation of in-situ stresses along the wellbore trajectory, but cannot obtain the macroscopic in-situ stresses distribution of the block (xie et al., 2021, shen et al., 2015).