| The Chang7 reservoir in the ordos basin is an important energy producing area for changqing oilfield with a steady output of 50 million tons.It is characterized by low pressure,low porosity and low permeability.More horizontal Wells are used for tight oil development.Compared with straight wells,the horizontal wells in ordos is more prone to borehole wall instability;directional friction increases and complicated underground accidents such as stuck drilling.Therefore,the research of environmentally friendly water-based drilling fluid technology suitable for tight oil horizontal wells will have great practical significance for ensuring safe,green and efficient development of tight oil and gas reservoirs.This paper aims at the characteristics of chang 7 reservoirs and the technical problems of drilling fluids in longdong region.Environmental protection drilling fluid treatment agent and new drilling fliud system were studied.The result of research shows thatNewly developed environmentally friendly water-based drilling fluid system has good performance of inhibition,sealing and lubricity.It also has good settlement stability and temperature resistance stability and reservoir protection effect whose permeability recovery value Rd was up to 80.6%?92.0%.This system has been applied to more than 30 Wells in several blocks of changqing oilfield.Compared with original system,this new system can increase the rate of penetration by 11.5%,the monthly rig rate by 14.2%,and without any downhole complex accident.Environmental performance test results of well slurry sampling are shown this system does no harm to the environment and the layer,which can be applied to the whole region. |
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