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Polycrystalline Diamond Compact (PDC) bits have shown individual directional characteristics in the deviated drilling of the 8-1/2" (216 mm) hole section in Unocal's Gulf of Thailand operations. The effective and successful use of those directional tendencies and the parameters that can affect them are described and illustrated with detailed examples in this paper. Five typical 8-1/2" PDC bits (Fig 1) make up a data base of over 200 "Rotary Bit" runs in low-toxic oil base mud through soft and medium soft formations. Bits used in correction runs on Positive Displacement Motors (PDM) and turbines Positive Displacement Motors (PDM) and turbines with or without the offset stabilizer are discussed. Introduction Unocal Thailand Inc., a subsidiary of Unocal Corporation, has developed major natural gas and condensate reserves in the Gulf of Thailand approximately 300 miles (483 km) south of Bangkok. Unocal, as operator on behalf of its co-venturers, South East Asia Petroleum Exploration Company and Mitsui Oil Exploration Company Limited has, developed four offshore fields capable of producing over 450 × 10 6ft.3/D (12.7 × 10(6) m3/D) of natural gas and 20,000 bbl/D (3180 m3/D) of condensate. Over 239 development wells have been drilled for this operation, which produces 30 percent of Thailand's commercial energy supplies. Cascading of technical developments and operational improvements through a long-term project of this magnitude has tangible benefits to project of this magnitude has tangible benefits to its profitability. The utilization of PDC bits and optimizing their effect on the drilling program have contributed significantly towards the program have contributed significantly towards the reduction of time and associated costs to drill the multiple-targeted development wells. PDC bits have been the subject of many papers since their introduction in the 1970's. Their ability to last for extended runs of over 3000'(8, ET. AL.) has provided extreme challenges to economic directional drilling. This paper will deal with Unocal's directional drilling experience in one location with a significant number of PDC bit runs. OPERATIONS Development wells are directionally drilled from a 12-slot wellhead platform with a tender assisted drilling rig. After surface casing is set, conventional 12-1/4" (311 mm) mill tooth bits and water base mud are used to directionally drill to 4500' (1372 m) total vertical depth (TVD) or 5000'(1524 m) measured depth (MD) reaching terminal angle and azimuth. 9-5/8" (245 mm) casing is set and 8-1/2" hole is directionally drilled with a low-toxic oil bass mud through a series of 3 to 5 stratigraphic or Structurally controlled targets to the total depth (TD) which averages 10,700' (3260 m)MD or 8700' (2650 m) TVD. A typical well schematic is shown in Fig 2. The maximum well angle averages 480, with many of the wells dropping off to vertical or near vertical in the 8-1/2" hole section. The productive Miocene gas sands are in highly faulted sand/shale sequences which range in depth from 4500 (1370 m) TVD to 9000' (2740 m) TVD.
Polycrystalline Diamond Compact (PDC) bits have shown individual directional characteristics in the deviated drilling of the 8-1/2" (216 mm) hole section in Unocal's Gulf of Thailand operations. The effective and successful use of those directional tendencies and the parameters that can affect them are described and illustrated with detailed examples in this paper. Five typical 8-1/2" PDC bits (Fig 1) make up a data base of over 200 "Rotary Bit" runs in low-toxic oil base mud through soft and medium soft formations. Bits used in correction runs on Positive Displacement Motors (PDM) and turbines Positive Displacement Motors (PDM) and turbines with or without the offset stabilizer are discussed. Introduction Unocal Thailand Inc., a subsidiary of Unocal Corporation, has developed major natural gas and condensate reserves in the Gulf of Thailand approximately 300 miles (483 km) south of Bangkok. Unocal, as operator on behalf of its co-venturers, South East Asia Petroleum Exploration Company and Mitsui Oil Exploration Company Limited has, developed four offshore fields capable of producing over 450 × 10 6ft.3/D (12.7 × 10(6) m3/D) of natural gas and 20,000 bbl/D (3180 m3/D) of condensate. Over 239 development wells have been drilled for this operation, which produces 30 percent of Thailand's commercial energy supplies. Cascading of technical developments and operational improvements through a long-term project of this magnitude has tangible benefits to project of this magnitude has tangible benefits to its profitability. The utilization of PDC bits and optimizing their effect on the drilling program have contributed significantly towards the program have contributed significantly towards the reduction of time and associated costs to drill the multiple-targeted development wells. PDC bits have been the subject of many papers since their introduction in the 1970's. Their ability to last for extended runs of over 3000'(8, ET. AL.) has provided extreme challenges to economic directional drilling. This paper will deal with Unocal's directional drilling experience in one location with a significant number of PDC bit runs. OPERATIONS Development wells are directionally drilled from a 12-slot wellhead platform with a tender assisted drilling rig. After surface casing is set, conventional 12-1/4" (311 mm) mill tooth bits and water base mud are used to directionally drill to 4500' (1372 m) total vertical depth (TVD) or 5000'(1524 m) measured depth (MD) reaching terminal angle and azimuth. 9-5/8" (245 mm) casing is set and 8-1/2" hole is directionally drilled with a low-toxic oil bass mud through a series of 3 to 5 stratigraphic or Structurally controlled targets to the total depth (TD) which averages 10,700' (3260 m)MD or 8700' (2650 m) TVD. A typical well schematic is shown in Fig 2. The maximum well angle averages 480, with many of the wells dropping off to vertical or near vertical in the 8-1/2" hole section. The productive Miocene gas sands are in highly faulted sand/shale sequences which range in depth from 4500 (1370 m) TVD to 9000' (2740 m) TVD.
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