| In recent years, the demand of oil and gas reservoir reform and unconventional oil and gas development increasing causes the drillable composite bridge plug staged-fracturing technology for horizontal well has rapidly developed as one of the main oil and gas transformation technology. Using the bridge plug and coiled tubing in layered fracturing, perforating, and bridge plug drilling is one of the new fracturing techniques. Fast, efficient and complete drill out these multilevel composite bridge plugs will provide reliable operation channel for the subsequent operation and avoid the column blocking or failure.This paper takes the well applied composite bridge plug and cylindrical cogging drill bit as the research object, based on elastic-plastic mechanics and cutting principle, derived the formula of feeding force and cutting depth for single tooth. The relationship between the drilling pressure and the feed force of a single tooth, the torque and the cutting force of a single tooth is derived considering the total structure of the bit. The drilling rate equation of the composite bridge plug is established considering the hydraulic parameters and the wear degree of the bit. The drilling rate equation of the composite bridge plug is established considering the drilling pressure, the bridge plug structure and material, the rotating speed and so on. Because of the difference of drilling single bridge plug and a bunch of bridge plugs, the restriction conditions of the two cases are discussed respectively. The optimization scheme of drilling parameters is presented. When the drilling object is a single bridge plug, the limit pressure, the rated torque of positive displacement motor and the corresponding drilling pressure are the key factors to control the drilling rate. When the drilling object is bunch of bridge plugs, in addition to the above factors, the displacement should be kept constant. The drilling rate of each plug is not necessarily the fastest.The drilling test of composite bridge plug was carried out in two wells with similar well condition. There are 13 composite bridge plugs in total, with 9 of them have stable data were particularly analyzed. Influence coefficients are modified combined with curves of drilling pressure and footage, bridge plug material property test and theoretical calculation formula. Influence coefficient of the center pipe, slip and wedge, packer rubber are 0.41, 0.17, 0.46, 0.38, respectively. The abrasion coefficient of positive displacement motor while drilling 1 to 4 bridge plugs are 0.92, 0.86, 0.80, 0.76, respectively. The modified general equation for drilling rate is used on the two testing wells in order to optimization the drilling parameter. After the optimization, the shortest drilling time of the 9 bridge plugs is 8min, the longest drilling time of the 9 bridge plugs is 19 min. |
