Objective In order to solve the blocking problem of high-temperature deep wells in Jianbei gas field, the component analysis of blockage and the preparation and performance evaluation of matching blockage removing agent were carried out.

Methods The ion content of the blockage after acid dissolution was determined by atomic absorption spectrophotometry, and the components of the blockage were analyzed by X-ray diffraction. It was found that the blockage was mainly CaSO₄. Taking maleic anhydride (MA), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylic acid (AA) and methyl acrylate (MMA) as raw materials, a blockage removing agent suitable for CaSO₄ scale was synthesized. The target product contained carboxyl and sulfonic acid groups was confirmed by the infrared spectrum. The performance of inhibiting calcium sulfate scale and dissolving calcium sulfate scale as well as the corrosion of scale inhibitor were systematically studied.

Results When the dosage of blockage removing agent was 3.0 mg/L, the scale inhibition rate was up to 97%. When the temperature was 80 ℃ and the amount of blockage removing agent was 4%, the best scale dissolving performance for CaSO₄ was 25.59 g/L, and the particle size of after-treatment field blockage decreased obviously, the particle size was mainly distributed in the range of 5-30 μm. The corrosion rates of produced water before and after adding blockage removing agent were 0.068 3 and 0.045 9 mm/a respectively. It was proved that the blockage removing agent has no corrosion and has certain corrosion inhibition.

Conclusions The blockage removing agent has a good performance of scale inhibition and dissolving to CaSO₄. It has no corrosion to oil casing-pipes. It can be used as scale inhibition and removal to CaSO₄.