The Research And Application Of Anti-sloughing Drilling Fluid For Horizontal Wells In Daniudi Gas Field

Borehole collapse is one of the most commonly complicated conditions in the process of oil and gas exploration and development.Complex situations which conclude borehole collapse were frequently encountered during drilling the mudstone of Shiqianfeng and Shihezi formation in Daniudi gas field of Ordos basin.The mudstone of borehole wall is easy to peel,which may cause the drilling accident such as pipe-sticking and bit balling.This paper analyzes the chemical instability mechanism of borehole in Daniudi gas field and evaluates the performance of drilling fluid used in Daniudi gas field.Rheology modifier and anti-sloughing sealer was developed in order to fit the characteristics that Shiqianfeng and Shihezi Formation which is easy to collapse and solve the problem of cutting bed in Daniudi gas field.Effective anti-sloughing drilling fluid system was designed which is suitable for Daniudi gas field.By means of XRD,shale expansion,rolling recovery and cation exchange capacity(CEC)experiments,the chemical instability mechanism of borehole was studied.Through the scanning electron microscope,infrared spectrum and nuclear magnetic resonance experiment,the characterization and evaluation of anti-sloughing sealer and rheology modifier were carried out.The plugging performance of drilling fluid system was evaluated by JHMD-II dynamic damage assessment instrument.The results show that the anti-sloughing sealer and rheology modifier can effectively improve the performance of the drilling fluid system,and the comprehensive performance of the high efficiency anti-sloughing drilling fluid system is better.The plugging rate of the new anti-sloughing drilling fluid system is as high as 93.2% and the dynamic filtration volume is only 2.6 m L.Its permeability recovery value of the drilling fluid system has reached 88.5%.The effective anti-sloughing drilling fluid system was tested on four wells in Daniudi gas field and can achieve better application effect.The performance of the new drilling fluid system is stable and easy to control.The borehole diameter expansion rate of test wells is less than 5.98% and the average shortening rate of drilling cycle is as high as 30.6%.In this application,the field construction technology of anti-sloughing drilling fluid is improved.