drill string .
随着井深的增加，钻杆内压力损失会增加。
91、a smaller hole usually is being drilled ,so less fluid volume is
needed to maintain the velocity to clean the hole. 小井眼钻进，较小的排量就可以清洗井眼。
92、balance is achieved by using smaller liners or plunger . 使用较小的缸套就可以满足要求。
93、the number and size of mud pits need will depend upon the
depth of the well ,specific mud requirements , and other related factors. 泥浆罐数量取决于井深和泥浆需求及其它因素
94、this can vary from a single pit on small rigs to over five pits on
large rigs. 因钻机大小不同，罐数量可从一个到五个。 95、mud pits range in size from 100to over 200bbl. 每罐的容积从100到200桶不等。
96、the working mud volume in a pit will usually average about 65
to 75% of the total calculated .volume after allowing for dead volume and top clearance. 有效容积，一般是整个罐计算容积的65%至75%
97、as a rule of thumb, the working surface mud volume should
be about one-half the hole volume . 经验法测，地面泥浆量大约是井内泥浆量的一半
98、this ratio allows sufficient surface retention time to permit
blending and mixing in order to maintain a constant, well-balanced mud system . 要保持井内泥浆无大幅度的变化，地面上要留有足够时间配
浆。 99、additions volumes causes excessive treating costs . 多余的泥浆会增加额外的成本
100、the most common rolling lone bit is tle steel-tooth or
milled-tooth, in which the teeth are milled on each cone. 最常用的牙轮钻头是钢齿钻头
101、 the insert bit has tungsten carbide inserts mounted in
holes in the cone rather having teeth milled on the cone . 镶齿钻头是碳化钨齿镶在牙轮上而铣出来。
102、the PDC bit provides faster , more economical way to drill in
many formation, they remove rock by shearing rather crushing or grinding as rolling cone bits do . PDC钻头提供了更为经济和更快的钻进方式，他以破碎地层是
通过剪切方式而不是压碰方式象牙轮钻头水样
