The outstanding problems in the process of deep well drilling in Daqing Oilfield are a high geothermal gradi ent (average 4℃/100m) and a low pressure coefficient (average 0. 98). In view of these geological characteristics, several factors are considered, such as reservoir protection, cost reduction,ROP enhancement etc. Four types of drill ing fluids are developed,which include 220℃ high temperature Water -in -Oil drilling fluid, 200℃ high temper ature Oil -in-Water drilling fluid, 200℃ high temperature organosilicon drilling fluid and 180℃ foam drilling fluid, and good results were obtained in the field.
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