Research on PDC bit for drilling in gravel interlayer

Abnormal conditions like instability of drilling,breakage of PDC,high wear of bit crown,low penetration rate and service life etc.will often occur when PDC bits were used to drill gravel interlayer formation,In order to relieve these conditions,the following two measures had been adopted in designing and manufacturing PDC bits:(1) to improve the working conditions of PDC bit,namely reduce or distribute the impact load acted on PDC bit which is related to designation of PDC bit structure.(2) to select proper PDC to reduce the conditions of its break or wear.Based on above two considerations,a kind of bit combination structure of bit crown with outside parabola-inside cone features and aided cutting edges has been adopted and PDC with non-plane multi groove binding is selected.The selected PDC can reach 750℃ in thermal stability,2.9×105 in wear resistance and more than 600 J in impact toughness.3 bits were produced according to the ideas and tried to drill in 3 exploration wells.All the three bits drill through the specified gravel interlayer and Guantao formations,while in the same formations in the nearby wells the drilling method using tri-cone bit first and then PDC bit.Had made a breakthrough in drilling the gravel interlayer formation which was not allowed to drill with PDC drill bits.These data show that drilling efficiency is improved by 26%,the new type of PDC bit has advantages in drilling gravel interlayer formation.