Study on the Wellbore Stability in Fractured Carbonate Formations in North Truva Area

doi:10.3969/j.issn.1006-6535.2021.01.024

Abstract

Abstract: The fracture development of carbonate formation in the Carboniferous Middle Bashkir Order (KT-II) in North Truva area has caused serious wellbore collapse during drilling.In order to improve the drilling efficiency,the fracture occurrence and inter-fracture filler of KT-II carbonate formation were studied,the carbonate matrix and inter-fracture filler components were tested,and the influence of fracture development on the pore permeability characteristics and mechanical strength of the carbonate formation was analyzed.At the same time,a theoretical model of wellbore instability in fractured carbonate formations was established by coupling the ground stress field,seepage field and fracture mechanical weak plane effect,and the prediction of wellbore stability in KT-II carbonate formations in North Truva area was carried out.The results show that:the development of fractures in the KT-II carbonate formation in the North Truva area and the prominent inter-fracture mechanical weak plane effect are the dominant factors inducing the wellbore collapse; the development of fractures strengthens the seepage migration of drilling fluid along the fractures and weakens the supporting effect of the drilling fluid on the wellbore; the fracture occurrence and wellbore trajectory have obvious effects on the stability of the wellbore in the carbonate formations,drilling in the direction of 180° to the dip angle of the fracture plane can bring the optimal wellbore stability,and optimizing the wellbore trajectory can effectively improve the wellbore stability in fractured formations.The results of the study reveal the mechanism and main influencing factors of the wellbore instability in fractured carbonate formations,and provide a reference for the design of wellbore trajectory and the selection of engineering parameters in fractured carbonate formations.

Key words: carbonate rock, fracture weak plane, collapse mechanism, wellbore stability, North Truva Area

CLC Number:

TE142

Zhang Yanna, Han Zhengbo, Kong Lulin, Chen Qiang, Liu Houbin. Study on the Wellbore Stability in Fractured Carbonate Formations in North Truva Area[J]. Special Oil & Gas Reservoirs, 2021, 28(1): 161-169.

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