Preserving well integrity with pre-job testing

The Netherlands is home to underground gas storage wells that are used to inject and store natural gas during summer months. Throughout the winter, the wells produce gas during peak delivery periods. To ensure that Nederlandse Aardlie Maatschappij’s (NAM) Grijpskerk Underground Gas Storage met its contractual obligation to deliver adequate gas during the peak period (total peak capacity 2,000 MMcfd) Well GRK-47 needed its production and injection rate restored. NAM performed a coiled tubing (CT) acid stimulation to restored the well’s capacity. The well’s performance declined by 52.5 MMcfd over the years, leading the operator to suspect scale, fines and/or drilling damage. Since the well was completed with pre-packed screens in a sandstone reservoir, the impairment increased the drawdown over the screen to 1,450 psi, jeopardizing screen integrity, as well. The screen has a differential pressure rating of 1,000 psi. An acid screen wash and mud acid squeeze was proposed to remove the impairment and reduce drawdown.