Key Mud Logging Technologies for Depleted Sandstone Gas Storage ——Case Study of the Wen 23 Gas Storage

The integrity of the wellbore is crucial to the construction of gas storage. Depleted sandstone gas storage experienced issues with faults and experienced several engineering problems such as the frequent occurrence of leakage and poor cementing quality in a salt-gypsum interval during drilling operations, which posed potential risks to the wellbore integrity. For this reason, the Wen 23 Gas Storage was studies as an example, and the key technologies in the mud logging of those gas storages were studied. By using the drilling/mud logging data of gas injection/production wells in the Wen 23 Gas Storage, combined with the preliminary exploration and development data, the wellbore integrity was evaluated from two aspects of caprock sealing and fault sealing. Thus caprock identification and evaluation methods were established on the bases of faulting and the absence of the salt-gypsum interval in Es₃ Member of this formation used for gas storage. With that, the discrimination modes for the reasons of lost circulation and the fault sealing evaluation methods were established on the basis of drilling fluid outlet flow curve variations and pattern. In order to improve the wellbore integrity, the methods for calibrating the intermediate completion depth while penetrating 5.00–10.00 m into the caprock bottom boundary were established on the premise of the salt-gypsum interval occurrence and missing in Es₃ Member of this gas storage formation. The practical applications showed that the key mud logging technologies based on the above methods could solve the problem of closed mud logging/evaluation for the wellbore sealing of gas storage from the perspective of geology and engineering, which helped to improve the strength and quality of mud logging support and service to gas storage construction.