Bottom-hole cementing plug technology for convex well in Mao 23 well of salt cavern gas storage

Well Mao 23 is one directional gas injection/production well of salt-cavern underground gas storage (UGS) in the Zhixiqiao subsag of Jintan Sag, the Jintan Basin. The convex shaped borehole which is small in the upper part and large in the lower part is formed during the completion of the second section. In addition, salt floor is penetrated in the process of drilling. As a result, the pressure test is not qualified. Therefore, it is necessary to adopt the cementing plug above the salt floor. The construction difficulties of cementing plug in Well Mao 23 were analyzed. Then, the cementing fluid systems were selected, e.g. the saturated saltwater prepad and the salt-resisting cement slurry system, and some technical measures were taken, including the “balanced” cementing plug and the cementing process of forward cementing and reverse circulating treatment of residual slurry. After 48 h wait on cement, the plug surface is tested to be qualified. After 30 min pressure test, the pressure drop is 0. Obviously, the cementing quality of the cement plug satisfies the construction requirements of salt-cavern UGS.