| Formation damage control is a strategic problem in field exploration and development, and it is also an important measure of improving well productivity. Nanpu Oilfield ? andПstructure reservoir have been studied, the result shows that basalt develops well in Guantao formation and it collapses easily. The content of montmorillonite, illite/montmorillonite and kaolinite is high relatively in Guantao formation and Dongyi zone. The main reservoir of Dongyi zone is strong to extreme strong water sensitive and moderate to extreme strong earth acid sensitive formation, which causes formation damage easily.Lab testing method and mechanism of drilling fluid damaging oil formation have been tested, lab evaluation equipment has been improved, multi-purpose drilling fluid HTHP dynamic comprehensive tester has been developed and the new lab testing method of drilling fluid damaging formation of constant effective stress method has been established. The influencing factors such as core permeability, positive pressure differential, temperature, shear rate, removal medium and solid phase type on core plugging ratio and core removal ratio are studied.In view of Nanpu Oilfield reservoir characteristic and latent damage factors, additives are evaluated and screened, and the systems of potassium film forming plugging low-invasion water-based drilling fluid brine system and fresh water system are optimized. In the same way, the property of two systems is evaluated. The result shows that the systems owe good rheological property and filtration property, strong inhibition, outstanding the tolerance of fouling, good lubrication, good plugging characteristic and good ability of formation damage control. Also, the advantage and mechanism of potassium film forming plugging low-invasion water-based drilling fluid system are analyzed. Field test is carried about the drilling fluid system, and the result shows that the system attains desired target and satisfies the demand of formation damage control.
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