Reservoir Damage Diagnosis and Acidizing Extended Effect Technology of Massive Sewage Reinjection Wells with Thousands of Cubic Meters

The sewage reinjection wells in Bohai C oilfield group with a daily injection volume of thousands of cubic meters which are facing the problems of sharp decline in injection volume and low efficiency of acidification. Using the integration methods of reservoir characteristics and rock physical property analysis, water quality survey and analysis, scaling prediction, software simulation, it is found that the main cause of damage of the well type is particle migration, and the damage radius is 0.3 m~0.5 m. The secondary cause of damage is scaling, solid plugging. The scaling type is calcium carbonate. The scaling amounts of the two kinds of injected water are 287.6 mg/L and 357.1 mg/L respectively. The solid plugging is mainly dolomite minerals, and the damage radius is 0.2 m. At the same time, it is analyzed that the reason for the low efficiency of acidification in the past is the use of online acidification process, which leads to the water injection volume of massive sewage reinjection well far exceeding the acid injection volume, the acid concentration dilution ratio is too large, and the acid can not effectively remove the compound damage. HLCHEM-Y acidification system was developed by using hydrochloric acid, acetic acid, fluorosilicic acid, HEDP main acid, citric acid, quaternary ammonium salt, SDBS and other additives can be used to solve problem of compound injur. The 3 m³/min~4.8 m³/min large displacement tug acid injection process is adopted to solve the problem of poor effect of low displacement acid injection process in massive sewage reinjection well under the limited space of offshore platform. The supporting technology has been applied in 16 wells of C Oilfield Group which has achieved significant results in extending the average injection rate increase from 116,000 m³ to 399,000 m³ after acidification, and the average validity period extend from 44 days to 152 days.