Halahatang oilfield in Tarim Basin is a typical ultra deep fractured vuggy carbonate reservoir, which is the main production area of crude oil in Tarim Basin. The wellbore instability is serious in Triassic and lower strata (the borehole enlargement rate is 22% – 31%). Due to the complex rock characteristics, the drilling cycle for single well is long (124 days on average), and it is difficult to speed up. Based on the log interpretation curves, the calculation methods of pore pressure, collapse pressure and fracture pressure profiles established, and the spatial distribution characteristics of three pressures in this area were analysed; The rock drillability, rock hardness, compressive strength and abrasiveness of the roller bit and PDC bit single well measured by laboratory tests. Based on the statistical regression method, the relationship between the above drilling rock mechanical parameters and logging acoustic time difference and the formation drillability profile single were studied. The research results guide the drilling design optimization and operation of 15 wells in Ha 8 and Ha 12 blocks, The average drilling cycle is reduced by 21% (from 124 days to 98 days), and the hole enlargement rate is reduced from 24% to less than 10%.
Halahatang oilfield is the main oil producing area in Tarim Basin, China. Drilling practice shows that in this area, borehole enlargement and borehole collapse are common, and the borehole enlargement is more than 20%, especially in the Triassic system. Borehole instability can leads to logging obstruction, sticking and other drilling complications[1-3]. In addition, due to the complex rock characteristics in this area, the single well drilling cycle is long (average 124 days), and it is difficult to increase the drilling speed. Therefore, this paper establishes three pressure calculation and formation drillability evaluation methods in this area by combining indoor test, mathematical statistics analysis and numerical simulation, to guide the safe and rapid drilling in the area.
