In making a drilling program, many drilling engineers try to find the best way to prevent drilling problems by analyzing another well data and consideration of technical calculations. However, once the drilling operation is started, people often come up against unexpected drilling troubles and can't move forward, taking much time and cost. Borehole stability problem is one of the most difficult trouble, because prompt measures should be taken to improve the well condition. And as each well has each characteristic, even if countermeasures which had an effect on another well, may have no effect on well that is drilled now. So it is very important to investigate the data of wells in detail which had met with borehole problems, and know the many method to deal with it, and hold these knowledge in common. I report a few cases about borehole stability problem, those wells were operated by Teikoku oil company and, would like to make good use of these knowledge to future wells.
Well A Bore hole stability problem was caused by caving of the formation which consists of tuff and dolerite. By increasing mud weight and viscosity, and doing short trip at regular intervals, flush high viscosity mud properly, well condition became stable, had no trouble after taking these way.
Well B Bore hole stability problem was caused by pushing plastic mineral from well bore. By checking and adjusting the MBC value, concentration of potassium ion, and doing short trip at regular intervals, well condition became stable, had no trouble after taking these way.
Well C Bore hole stability problem was caused by caving of the formation of basaltic tuff. By increasing the YV value in drilling mud, improving cutting transport ability and adjusting mud weight, well condition became stable, had no trouble after taking these way.
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