Analysis And Optimization Of Drilling Technology Of GSN-001 Coal Seam Gas Well In The North Of ShiZhuang Area

The coal bed methane is unconventional gas resources in the coal seam automatically living and storing up. Making hole in the coal bed methane is common and special compared with making hole in the oil gas bed.1.In the drilling process, the coal bed is damaged easily . one is the drilling fluid intruding into the coal bed, when the drilling fluid Intrudes into the coal bed , horniness Precipitates are formed because of the chemical reaction between the drilling fluid and the water in the coal bed. Thereby the gangways are filled and walled up, and the osmosis of coal rocks is reduced. The other of coal bed damaged is the pressure sink between the drilling fluid pole and the ground.2.The mechanical strength of coal is low , and could not prop up the pressure of the over formations, and is prone to fall and break up to cause the hole well extend.3. When the coal seam broached, the longer the soak time is, the more seriously the coal seams fall down.To reduce the pollution of the coal seam, the drilling speed must be expedited, and the soak time must be decreased, and the drilling cycle must be shorten, and the differential pressure must be decreased. So we can enter on doing something from two sides, one is to decrease strivingly the solid content of drilling fluid, the other is to adopt the balanced drilling that the air or froth drilling is adopted above the goal coal seam and the water balanced drilling is adopted in the goal coal seam.The traditional turntable drilling technics with mud was adopted in the GSN-001 well for coal seam methane .In the drilling process, the dentes of PDC drill bit and the thricone rock bit mangled, and the liner of mud pump is replaced frequently for abrasion, and the screw thread of drill stem also mangled, moreover, the drilling parameters in the drilling process was not rational. As a result, the drilling efficiency was low and the drilling cycle was long, and these were disadvantageous for the exploiture of the coal seam methane drilling.Some researches were carried on as follows:1. In allusion to the mangle of the dentes of PDC drill bit and thricone rock bit, the dentes model was founded at first, and then the maximum portrait force was worded out through coordinate transform. Because the rocks are broken by dentes with static load and dynamic load, the dynamic models in the high frequency vibration force and low frequency vibration force were separately deducted, and finite element method was adopted to analyze the models with their maximum value.2. In the actual drilling process, the process of dentes touching the stratum is very complex, so the model was predigested in this text. And supposing the transmission ratio of the cone body to the thricone bit was same, and one of three was selected to analyze for representation. The dentes were analyzed in the margin status through the sole calculation, and one dens touched the stratum, two dentes touched the stratum, three dentes touched the stratum were statically analyzed at first, moreover, non-linear contact finite element method was adopted to analyze for actually simulating the dens intruding into the rock.3. In allusion to the intensity of the screw thread of drill stems, the drill stem reversion and the drill stem vibration were analyzed. And supposing one drill pipe was not contacted with the well hole in the rotation process, and only reverse joints in two ends were contacted with the well wall. Subsequently the maximum flexural stress was worked out in the one drill pipe reverse status compared to the fatigue strength of the screw thread.4. In allusion to the low drilling efficiency, the drilling parameters and the drill tools assembly were analyzed and optimized, and the rheologic property of flush fluid was advised to improve to increase the drilling efficiency, and the solid control equipment system was improved to increase the drilling efficiency, and the mud drilling technics was combined with the air drilling technics.The reason the dentes were damaged in the drilling was the vibration d of the rill string on the one hand and on the other hand was that the moment pressure was so rapid that the load of dentes was too large. To avoid the similar questions appear again, the drillers must operate properly the machines, and the absorber should be installed on the drill tools at the time of high rotatory speed, and the dens should be optimized in the structure and material; The reason for the invalidation of the screw of drill string in the drilling process was the reversion that caused alternating bending stress that would cause the fatigue of the drill string to rupture in some weak parts on the one hand, and on the other hand was that there was not effective solid control system in the locale to lead the abrasion of the drill string and the fatigue of the screw thread. In allusion to this situation, it is necessary to add the high lubricative mud to the circulation medium to reduce joint the friction between the joints and the well wall.The structure of threadneed be optimized to avoid the thread of joints invalidation and the transition connector should be changed in time in the scene and the effective solid control system is necessary to reduce the friction;The reason that the drilling efficiency was too low was many, including the improper drill bit, the small WOB and the bad rheology of the drilling fluid and so on. For the low drilling efficiency, we can adopt Downhole Hammer Drilling technology combined with the rotary table rotary drilling technology ,and the drill stem was improved in the text and the drill collar of Φ178mm was abandoned, and the life time of the drill stem was prolonged and the accidents were reduced to achieve the higher drilling efficiency. There was significant for the exploration of the coal seam methane well in this section after the drilling technology was improved.