Located in south of Eastern Venezuela Basin,Orinoco Oilfieldis an on-shore heavy oil field in South America.The heavy oil is known for its high content of acids,heavy metals and asphaltenes with a viscosity of 1000~ 10000mPa · s.According to the reserve report released by PDVSA by the end of 2016,JUNIN Block that is situated in east of Orinoco Oilfield has an OOIP of 178×108bbl.Data of drilled wells were and distances between offset horizontal intervals were both studied to improve ultimate production rates.3-dimension borehole trajectories were de-signed and the most effective anti-collision measures were taken.After optimziation 8 ~ 12 horizontal wells are distributed on one pad.As the horizontal interval extends,the stable production time is prolonged and the accumulative production per well improves.However,the recovery rate stops increasing when the horizontal interval is over 1600m in JUNIN Block.Economically a large space between offset horizontal intervals results in fewer wells and lower costs,but a smaller space contributes to a higher production efficiency per well.If the space exceeds 600m,the accumulative production rate increases much more slightly.A three-dimension well trajectory consists of a vertical interval,an angle building interval,an angle holding interval,an angle building & direction changing interval,a direction turning interval as well as an absolute horizontal interval.Based on existing well patterns all wells with 3-dimension trajectories have been placed appropriately on their pads.It is proved that the optimized borehole trajectories and anti-collision measures are effective in overal field development.