Study on Wellbore Instability Factors of Igneous Rock Formation in Bozhong
Bozhong A Oilfield,located in the Bozhong Block of Bohai Oilfield,is the first oilfield to develop ig-neous rock formation in Bohai Oilfield.The igneous rock formation is prone to collapse and leakage during drill-ing,which seriously restricts drilling aging.Based on well logging data,physical experiments and drilling com-plex phenomena,the igneous strata of Bozhong A oilfield are finely divided and described in detail,and the com-plex performance of different igneous strata is analyzed accordingly in this article.Through finite element analy-sis,the influences of elastic modulus,Poisson's ratio,drilling fluid density and well inclination angle on wellbore stability are analyzed.The results show that there are clay minerals in basalt,tuff and tuffaceous sand and mud-stone,and most of them are filled in rock fractures.Among them,basalt mostly developed closed fractures,tuff and tuffaceous sand-mudstone developed as open fractures,tuff and tuffaceous sand-mudstone developed wider fractures and better connectivity,which also resulted in basalt mainly collapsed block,tuff and tuffaceous sand-mudstone mainly leakage;Numerical simulation also proves that basalt has a large elastic modulus and a small Poisson ratio,so it is more likely to collapse under drilling fluid immersion,and tuff and tuffaceous sand mudstone are more likely to induce leakage.Finally,corresponding technical measures are put forward based on the above a-nalysis,and good production results have been achieved in field application.
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