Research On Improving Drilling Speed Technology In Deep Wells Of Jiulongshan Structure

Jiulongshan structure is located at the northern Sichuan province, which has the following problems:complex structural geology, poor rock drillability, drill bit easy to wear, the lower formation with low pressure and easy lost circulation and the upper formation with abnormal high pressure as well as low rate of penetration with long drilling circle. This has restricted the Jiulongshan region’s exploration and development severely. Therefore, in order to raise the penetration rate and cut down the drilling cycle, the paper has carried out the speeding-up technique of Jiulongshan structure.On the basis of studying present situation of geological and drilling, this paper summarizes difficulties of drilling in this area and poses two sets of casing program for raising the penetration rate. The influence relationships of confining pressures on rock mechanics parameters have been obtained by experimental studies. Accordingly, the influence of confining pressures on rock drillability has been investigated and PDC bit selection method has been proposed. Drill bit has been optimized according to the rock drillability and abrasiveness. Through indoor experiment that confining pressures influences on rock mechanical property and logging data interpreting result, Rock drillability values can be reduced by 1 to 3 by the use of gas drilling. By establishing the distribution of formation stress near wellbore area and combining with stratigraphic leak, formation water production and displacement between formation water and drilling fluid, the paper has established the discriminant model of wellbore instability with gas drilling and proved feasibility of improving the drilling rate with gas drilling. The calculation model of minimum air rate has been established with the consideration of carrying debris and formation water production. The influence of drilling rate and formation water production on gas injection pressure has been analyzed and minimum air rate and gas drilling parameters has been optimized.After applying the set of speeding-up technology, for the well aiming at xujiahe formation, average rate of penetration of vertical well is 3.82m/h increased 36.43% compared with the implementation of the project of 2.80 m/h. Average rate of penetration of controlled directional well is 3.91 increased 57.66% compared with the implementation of the project of 2.48 m/h.Through bit selection, gas drilling and optimization of well program, the rate of penetration for deep wells has been improved and the drilling cycle has been shortened greatly. The speeding-up technologies have important reference values to similar structures for improving drilling rate.