| In recent years, water qualities deteriorate quickly in Daqing external eastern oilfields due to waste water re-injection or water and waste water mixed injection has been applied. The formation damage is increasingly serious in low to medium permeability oil reservoirs. Water injection rate decreased and injection pressure increased quickly. Though many shutoff removing measures were applied in Song-fang-tun, Sheng-ping, Pu-tao-hua oilfields, there are few effects. Original acidizing fluid has so quick reaction rate and low activity that it can only reach very small acidizing radius despite its 3-meter penetration. So enlarging acid volume can not increase effective acidification radius, whereas lead to erosion in near well-bore zones. Deeper formation damage can not be avoided.Based on above troubles, started with acidizing mechanism of acid-rock reaction and combined with mineral character of feldspar enriched in external eastern Pu-tao-hua strata, a novel organic retarded acid with performances of low reaction rate, long-distance penetration and low damage is studied. Systematic sandstone matrix acidizing experimental methods for acid-rock reaction and secondary damage mechanism are established. By applying the field techniques of well-bore pre-treatment and acidifications without spent acid flow-back, the acid with retarded character can penetrate into deep formation. Personal design of single well acidification is reached, theoretical analysis level of injection well acidizing and stimulation effect are improved. 35 wells have been performed with an average of 2.0 Mpa pressure drop, 168.4% injection increment per well at initial stage, and average effective lifetime is 9 months. It proves that the in-depth acidification technology has better adaptability to external eastern strata. The problems of water contamination in external Pu-tao-hua strata, shutoff removing and injection increasing in repetitive acidizing wells are settled.
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