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What are the implications of lithology bit failure


Influence of lithology bit failure in the performance of the drilling process: impact drilling speed, drill footage; the drilling process appears well leak, blowout, well collapse and sticking complex situations; make mud performance changes; borehole effects quality as well deviation, well diameter irregular, thereby affecting the quality of cementing. By analyzing the lithology and its effect on the drilling process, the drill bit selection and use of reasonable judgment.

    Clay, shale and shale effects: easily absorb water and mud free expansion, the well diameter narrowing, causing drill Difficult, even sticking with the extension of immersion time, will produce peeling off the block, the well enlargement, resulting in well collapse. You should try to use water or a low proportion of low viscosity drilling mud. Carbonaceous shale coupling is weak, easily collapsed. Argillaceous soft rock, drilling speed, but also easy balling.

    Sandstone: their nature are very different depending on particle size, composition and cements. The finer the particles, the more particles of quartz, silica and iron, the more the more hard cement, the greater the wear on the drill, such as quartz sandstone; the more argillaceous cement, more mica and feldspar component is softer Easy drill; the more coarse particles, the less cement, better permeability, easy to produce mud permeability loss and the formation of thick mud cake on the borehole wall, causing sticking adhesion complex situation, resulting in non-drill Normal use.

    Conglomerate: conglomerate drilling in easy to produce jump drill, drill limp and wall collapse; when a small displacement pump or low viscosity mud, gravel particles are easy on the back, drill bit body and teeth damage large cone.

    Limestone: Usually hard, slow-speed drill, less footage. There are some tunnel development sewing, sew when drilling holes, drill limp caused by venting mud losses, and sometimes after the well blowout leakage will occur.

    Limestone formations to drill footage, ROP and bit failure greatly affected. In addition, the local hard and soft layers staggered, such as hard shale and sandstone and white, easy to produce inclination; dip is easy to produce large deviation. Drill deviated drilling is easy to damage. When the rock contains soluble salts, such as gypsum layers, rock salt layer, etc., it will destroy the mud performance, affect the normal use of the drill bit.

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