Use of Low Solids Potassium chloride - Polymer Inhibitive drilling fluids emerged as an answer to minimize drilling related problems arising from sensitive clays and shale such as borehole instability, torque, drag, build up of low gravity solids, bottom hole fill, stuck pipe attributed to clay/shale hydration. Further improvisement of this drilling fluid system has been done by incorporating clouding out Polyol (equivalent to Clouding out Glycol) for enhanced inhibition and borehole stability. In ONGC it is extensively used successfully to drill high tech wells such as high angle /high drift / horizontal wells in development fields. Exploratory wells are mostly being drilled using dispersed drilling fluids to exploit the convenience of achieving higher drilling fluid specific gravity but wash outs have been problematic in Assam Fields especially in deep shale-coal- sand stone alterations.

Penetrating through troublesome shale coal sequence poses formidable challenge in smooth well completion. ONGC Assam Asset after careful selection used KCl-Polymer Clouding Out Polyol drilling fluid in deep exploratory wells in Assam field. Performance of this drilling fluid in providing borehole stability and more importantly attaining and sustaining higher fluid specific gravity in drilling and in combating well activity has been eventually established. More than five deep exploratory wells have been successfully drilled and two are being drilled in critical interval. Out of these activity in three wells have been successfully subdued using this system with high specific gravity up to 1.9 at the time of writing this paper. Further Pilot test has favourably indicated that given opportunity the above fluid will hold satisfactorily to specific gravity 2.0 without pumpability and Barite sagging problem.

Performance of KCl-Polymer Clouding Out Polyol drilling fluid in drilling especially shale coal-sand/shale-sand sequence of deep exploratory wells in Assam field and the benefits derived out of it have been discussed in this paper.

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