Study On Reservoir Protective Technology Of Drilling Fluid & Completion Fluid In Hafaya Oilfield,Iraq

Oil and gas formation damage control technology is one of the key technologies in oilfield development and production at home and abroad,which is much important to the development of oil and gas oilfield.The lithologic character and physical property of main reservoirs in Hafaya Oilfield are complex and diverse,and there are serious reservoir damage problems during the course of drilling and completion.Therefore,it is urgent to carry out the optimization of the research on drilling & completion fluid.Based on the characteristics of main reservoirs in Hafia Oilfield,the petrophysical and structural properties of S,M and N reservoirs were analyzed experimentally.The reservoir damage mechanism of three reservoirs was discussed combined with reservoir sensitivity experiment.The porosity of S reservoir belongs to middle & high range,and permeability belongs to low & super low range.The content of clay mineral is low.The velocity sensitive,water sensitive,salt sensitive,and alkali sensitive are weak.The stress sensitive damage.is medium weak.While the hole throat radius is small,which prones to water lock damage.The main mineral of M limestone reservoir is calcite.The pore throat size is larger.The main damage mechanism are solid plugging and stress sensitivity damage.The porosity of N reservoir belongs to middle & high range,and permeability is high.The main mineral of M limestone reservoir is calcite.The pore throat size is larger.The main damage mechanism are solid plugging,water sensitive damage and salt sensitive damage.Experiments show that rheological property,rejection capability and pollution resistance performance of on-site drilling & completion fluid are good.But the fluid loss(HTHP),lubrication and reservoir protection performance are not ideal.Based on the analysis of reservoir damage mechanism,the technical countermeasures of drilling and completion fluid are established.For the S reservoir: reduce the surface tension of the drilling fluid and the interfacial tension of the oil and water;improve the plugging performance;and reduce the loss.For M and N reservoirs: improve the quality of drilling mud cake,reduce the loss of drilling fluid;use the appropriate type of temporary plugging agent to improve the plugging performance drilling fluid.While improving inhibition of N reservoir drilling & completion fluid.For the S reservoir,the ultra low permeability film forming agent SDN-1 and the waterproof lock agent SD-WB are preferred.For the M and N reservoirs,acid-soluble calcium carbonate with different particle size was optimized as the bridging particles,and the oil-soluble resin ZX-8 was added as the deformation-filling particles.At the same time,the polyamine shale inhibitor SDJA-1 was added to improve the inhibition of N reservoir drilling & completion fluid.In view of the shortcomings of on-site drilling & completion fluid performance,the high-temperature fluid loss agent DYFT,lubricant RT-101 and SD-505 are optimized.And finally three sets of drilling & completion fluid formula are formed,the reservoir protection performance is excellent(core permeability recovery value ?95%),high temperature and high pressure filtration loss below 12.0mL.Rheology and lubrication are better.