Wellbore Stability of Igneous Rock and Drilling Practice in Shunbei Block

Abstract

Shunbei area is located in the northern margin of shuntuo low uplift structural belt, which is rich in oil and gas resources. There are many complex problems in the process of igneous rock drilling in Shunbei block, such as borehole collapse and stucking, which seriously restrict the progress of the drilling. To solve this problem, the project team firstly determined the composition, microstructure, mechanical properties and other parameters of igneous rocks in Shunbei block through mineral diffraction analysis, scanning electron microscope and rock mechanics experiment. The test results show that the igneous rocks in the unstable section of the shaft wall in this area do not contain expansive clay minerals, and the hydration capacity of the rocks is weak, but the micro fractures are developed. Secondly, based on the characteristics of igneous rocks, a dual fluid medium wellbore stability model considering both fractures and pores is established. The model simulation results show that the drilling fluid invasion into the formation will aggravate the fracture weak surface damage. The longer the drilling fluid immersion time, the deeper the invasion, and the higher the collapse pressure around the wellbore. Finally, according to the microstructure and physicochemical properties of igneous rocks, the key points of anti sloughing drilling fluid technology research and development are determined. The drilling fluid needs to be characterized by strong inhibition and strong plugging. Based on this idea, the potassium sulfamate drilling fluid system and formula are optimized. The laboratory test results of the optimized formula show that the performance of the drilling fluid meets the drilling requirements of igneous rock formation. Through the above analysis, the project team has established a set of anti sloughing drilling fluid system suitable for igneous rock formation by combining mechanical and chemical methods. The drilling fluid is of positive significance to ensure the drilling safety of igneous rock, shorten the drilling time and improve the drilling quality.

Copyright 2022, IFEDC Organizing Committee.

This paper was prepared for presentation at the 2022 International Field Exploration and Devel-opment Conference in Xi’an, China, 16–18 November 2022.

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