Publish Time: 2021-09-10 Origin: Site
There are many factors to evaluate the performance of a PDC bit, of which drilling speed is an important aspect, so what factors affect the drilling speed?
Here is the content list:
●Influence of geological factors on drilling speed
●Influence of unstable borehole on drilling speed
●Influence of Long borehole of large size on drilling speed
The strata were deposited far back in time, and the strata are hard and inhomogeneous, with high abrasiveness in some sections. The mud shale and sandstone interbedded in the Ziliui Formation with thickness above 500m, the sand mudstone is dense and hard, and the mudstone interbedded with quartz sandstone in the Sujiahe section is siliceous colloidal, and the rock hardness reaches grade 7; the rock drillability grade value of the Permian Yangxin Formation is 4.7-7.5, and the rock softness and hardness vary greatly, because of the high circumferential pressure, the hardness of the Permian tuff is more than 3 times higher than that of the Triassic, and the central zone has flint nodules, coal, and pyrite.
The formation pressure system is complex, ranging from negative pressure to abnormally high pressure, with a variety of pressure systems in the longitudinal direction and relatively independent pressure systems in the lateral direction. Carbonate gas reservoirs have 3 types of production formations: fracture, pore, and fracture-a-pore. The pressure regularity of pore gas reservoirs is clearer and shows normal pressure, which can achieve balanced drillings, such as the Chuandong Carboniferous System and Changxing Bioreef. In contrast, the pressure of fractured gas reservoirs depends on the strength of the geological movement and the strength of the rock itself-poorly regular and difficult to predict. Drilling with high-density drilling fluid according to the presence of fractures. It leads to overbalance affecting the mechanical drilling speed, but the risk of sudden fracture blowout is high when low-density drilling fluid is used for fast and strong drilling. The two high-pressure producing formations, Yangxin Group and Changxing Group, have a high-pressure gradient, high rock hardness, and deep stratigraphic depth, and the drilling fluid density is usually 1.50g/cm3; (the highest pressure gradient of Yunan 6 well reaches 2.45MPa/, hm, and the drilling fluid density is 2.41g/cm3), resulting in the drilling speed hovering around 1.00m/h for a long time.
The upper part of the Shaximiao Formation is a Pearlchong Formation formation in the high steep tectonic well in east Sichuan (well depth 0-2500m), the lithology is mainly sand, mud, and shale interbedded. Due to the strong water sensitivity of the rocks and the combined effect of the ground stress of the high steep structure, the borehole was easily destabilized and the good wall collapsed severely. To balance the collapse, the drilling fluid density is increased, resulting in a significant decrease in the mechanical drilling speed, for example, the drilling fluid density in the Shaximiao and Ziliujing formations of the Tiandong 26 well is increased to 1.35-1.63 g/cm, and the "pressure-holding effect" generated by the high fluid column pressure reduces the mechanical drilling speed to 0.96 m/h. The Longtan and Liangshan formations of the Permian The Longtan and Liangshan formations of the Permian are also very easy to collapse.
Imm borehole sections are larger than 311. Imm accounts for about 1/2 to 3/4 of the total footage in the east Sichuan area, and the drilling pressure cannot be increased due to the good slope factor. The drilling pressure of the PDC bit can only be increased to 120-180kN and the speed is 60r/min. The volume of rock breakage of the in PDC bit is large in large boreholes, for example, the volume of rock breakage of the in PDC bit is 4.24 times that of the 8Min bit and the volume of rock breakage of the in bit is 2.08 times that of the in a bit, the mechanical rock-breaking energy of the PDC rock bit at the bottom of the well is seriously insufficient, and it is difficult for the teeth to eat into the formation. The rock breaking method is mainly grinding rather than volume crushing, resulting in the efficiency of the PDC rock bit. Due to the large borehole size and deep well, the actual annular return velocity is below 0.8m/s and the hydraulic energy is also seriously insufficient, resulting in poor bottom cleaning effect and repeated rock chip crushing; meanwhile, the deep well drilling experience shows that as the large size well section deepens. The lame jump phenomenon of the tooth wheel bit is especially prominent, and the effective drilling time of the PDC bit at the bottom of the well is less than 50%, which also seriously affects the increase of the mechanical drilling speed.
Hejian Hengji Bit Manufacture Co., Ltd.’s drilling speed is far ahead of its peers. And we have professional technical support. We are looking forward to working with you!