An Integrated Solution in Utilizing Active Magnetic Ranging to Seal Off Underground Gas Storage: Theoretical Analysis and Field Test

Summary In this paper, we describe a comprehensive technology based on an active magnetic ranging system (AMR) for sealing off the cement plug (CP) in the open hole (OH) section of the wellbore below the existing CP for underground gas storage. Utilizing depleted oil and gas reservoirs for natural gas storage is an important approach toward achieving carbon neutrality. Sealing off old wellbores is prioritized according to relevant standards. The challenge with OHs with CP is that there are no magnetic beacons in the wellbore, and the extent of compaction is unknown. Accurate placement of the seal-off CP is crucial because current technical methods, such as electromagnetic and acoustic waves, have limitations. Magnetic ranging technology, which is mature and widely used for wellbore interceptions or collision avoidance, requires magnetic beacons such as steel casing, drillpipes, or bottomhole assemblies left in the borehole. On the other hand, acoustic positioning techniques are applicable but presently complex to run operationally. In this paper, we propose a comprehensive control technology. It starts by measuring the positional relationship between the subject wellbore (SW) and a magnetic beacon wellbore (MBW) using AMR. The data are then used in combination with additional skew data along with associate positional uncertainty or ellipse of uncertainty (EOU) to determine the location of the target wellbore (TW) and the MBW. By calculating the relative positional relationship between the SW and the TW, OH reentry below CP can be achieved within the EOU below the sidetracking point. After reentry, specific work such as crushing, element logging, caliper logging, and full hydrocarbon gas detection is performed to verify if the TW is still in the original position and if the caprock is properly squeezed and sealed off. The comprehensive technique or method was tested on five wells in the Bohai Bay, successfully assessing the position of the OH wellbore and reentering below the CP. The process system expands the field of AMR and demonstrates significant industrial application value. It provides a new means of sealing off complex old wells.