Study and Field Application of Calcium Sulfate Scaling in Fractured High Temperature Bedrock Gas Wells

The reservoir temperature of Jianbei and Dongping gas fields in Qaidam Basin is 170 ℃, and the scale deposits are diverse, which poses a great challenge to the study of calcium sulfate scale dissolution, problems affecting gas well production and test operation. In this paper, through analyzing the composition of scale sample, defining the scaling mechanism, investigating the scale dissolving method, the scale dissolving research is carried out for the scale sample on the spot, the formula and technology of carbonate displacement scale dissolution and acid organic phosphoric acid scale dissolution were formed by distinguishing the deposit of Wellbore scale sample and reservoir scale formation respectively. The results show that the sample is composed of high-purity calcium sulfate and a small amount of carbonate and iron, and the source of the sample is the scaling ion in the formation water with high salinity The carbonate phase displacement scale dissolving method is suitable for calcium sulfate scale dissolving in wellbore. The high temperature of reservoir can reach the required reaction temperature and has no corrosion to wellbore string The acid organic phosphate chelating agent scale dissolving method is suitable for the calcium sulfate scale dissolving in the drill hole and near the well of the reservoir, and can be combined with the corresponding acidizing liquid system to develop the complex acidizing process at the same time, which can slow down the formation damage caused by the secondary precipitation. Finally, two sets of scale solubilizer formulation and corresponding scale dissolving process are formed, which can effectively dissolve reservoir calcium sulfate, solve the field technical problems, and make great contribution to increasing and stabilizing production of gas field.