At present, Ordos Daniudi gas field is developed with the gas of Shan-1 and He-1 reservoirs, whose lithologies mainly are tight sands. The reservoirs have severely potential formation damages, induced by mechanisms such as strong water-sensitivity, water-blocking and solid slugging with small particles. The solid-free brine completion fluids are usually used in Daniudi gas field, but it had little positive effect on the formation damage relieving, sometimes even aggravated formation damage. This article has developed a new bio-enzymatic completion fluid. The laboratory test results showed that the completion fluid can thoroughly clean out the mud cakes, evenly relieve the pore slugging damage, and greatly reduce the formation water-sensitivity and water-blocking damages. It is also environment- acceptable without any toxic materials. The completion fluid has been applied in 15 horizontal wells in Ordos Daniudi gas field. The results of applications showed that the skin factors of all wells obviously decrease, especially in Well DX-1, the skin factor decreases to -2.3, and the Shan-1 formation has firstly got a good production without any stimulation treatments. The productions of all the wells are more than double times than those of former adjacent wells.

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