Application of acid soaking to release stuck pipe technology in Well Tazhong-11 and relevant understanding

Well Tazhong-11 encountered two leakage zones and one high pressure zone, and there were several different pressure systems in one open hole. The drilling complexities made the drilling fluid properties become poor, and the deterioration of sand carrying property of drilling fluid and increase of filter cake drag increased the probability of occurrence of pipe sticking. Pipe sticking occurred two times during drilling. The sticking formation was carbonate reservoir, so the acidization technique which is used in oil test and downhole service was used to release the pipe sticking incident. Practice shows that the technique of acid soaking to release stuck pipe is an effective means of releasing pipe sticking in carbonate reservoirs, and it is also favorable for reservoir protection and has good economic benefits and high technical feasibility. But further analysis and research need to be conducted to its use in oil/gas wells with large leakage, high casing pressure and high sulphur content and the effects of acid soaking to release stuck pipe on subsequent operations.