Research On Mechanism Of Coupling Flow In Carbonate Fracture Network And Wellbore

The Carbonate formation is well-developed structural fracture network.During the drilling process,the Carbonate formation which is likely to be influenced by narrow mud weight window and volatile wellbore pressure,that may cause lost circulation or other underground complex accidents.It is necessary to understand the typical fracture network,to establish the reasonable coupling theory and geometric fracture network and wellbore model,even to study the coupling regulation of fracture network and wellbore.This paper studies the outcrop profile of carbonate fracture networks from Leikoupo Formation to Changxing Formation,northeastern Sichuan.Based on this,it is likely to establish the corresponding fluid-solid coupling flow theory and geometric model for the two typical carbonate fracture networks,respectively.Besides,combined with the drilling shaft operating conditions and carbonate rock formation geotechnical environment,we intend to study the coupling carbonate fractures and wellbore under multi-field.The main contents and achievements are shown as below.(1)This paper summarizes two typical fractured networks:thin-layer fractured network and medium-thick-layer fractured network,and analysis the characteristic of the fracture networks from Leikoupo Formation to Changxing Formation.(2)Acquired the geology parameters of Yuanba X well from Leikoupo-Changxing Formation,collected the carbonate rock outcrops and obtained the basic parameters of rock mechanics by laboratory triaxial rock mechanics experiment.(3)Based on the digital image processing technology,the geologic profile observation is described by Image J software that established a geometric model for the thin-layer fracture network and the wellbore coupling flow.The dual medium theory model,a theoretical model of fluid-solid coupling in medium-thick layer fractures is established for the characteristics of medium-thick layer carbonate fractures.The true fractured surface is based on the geometric fractal theory,and the geometrical model of medium-thick layered fracture network and wellbore fluid-solid coupling is established.(4)The distribution law between thin-layer fracture network and wellbore,that analyzed and compared in case of drilling a single crack,drilling multiple cracks and drilling the matrix.At the beginning of drilling encountered cracks,a short-opening phenomenon may occur near wellbore,while the degree of opening is small,andthe penetration rate within the cracks would increase.When drilling the matrix,the coupling effect between wellbore and formation has a little effect on the crack network nearby,which only leads to the rise of pressure within the matrix near the wellbore.(5)This paper analyzes the law of coupling between medium-thick-layered fracture network and wellbore in case of considering joints in matrix and ignoring joints in the matrix.The loss rate and the cumulative loss increases obviously when the joints in the matrix areseparated from the fractured network and the wellbore seepage flow in the joints of the matrix.Considering the effect of joint joints between the fracture network and wellbore coupling seepage,that in line with more realistic drilling completion environment,would target more precise calculation results.