Two (2) steam flood vertical injection wells are under operation for the last 15 months in a two- pattern pilot. Previous steam injection experience in this reservoir did not indicate serious issues due to the short injection periods for cyclic steam stimulation (CSS) but several well integrity issues have been faced during the steam flood period. Key issues include high wellhead growth, steam leak to the annulus A, annulus between 7” production casing and 4-1/2” injection tubing, and groundwater vapor behind 9.625” surface casing. Negative impacts from these issues on the continuity and effectiveness of the steam flood are recognized and need to be resolved comprehensively. All wells in the steam flood pilot were drilled and completed based on designs and procedures according to thermal well compliance including well equipment, and cementing specification. Production casing was equipped with thermal expansion collars to support reduction in wellhead growth. Completion strategy uses seal bore packer with bore extensions to accommodate tubing movement and Vacuum-Insulated-Tubing to provide maximum thermal insulation. However, the presence of a total- loss zone near the surface (starting from 50 m depth) affects the cement isolation between surface casing and 12.25” open hole. Daily monitoring is performed on each well where key injection parameters and well responses are recorded. Maximum wellhead growth reached 61 cm within the first week and steam leak from the injection string to annulus A started after 6 months of steam injection. Soon after that, groundwater vapor starts to arise from the gap between 9.625” casing and 12.25” open hole. These series of failures occurred in both injection wells within 3 months apart from each other. It is believed that the steam leak to annulus A resulted in thermal transmission to groundwater vapor. Hoist entries to both injectors indicated that Injector-1 has tubing seal assembly stuck inside seal bore and resulted in parted tubing collar while Injector-2 has tubing seal assembly damage. Both wells have thick oil covering the retrieved seal bore packer. Remedial actions were performed, including a complete change-out of the seal bore packer assembly and top-job cement fill up to surface using fast-set cement to isolate the gap between 9.625” casing and 12.25” open hole to reduce wellhead growth. As a result, the maximum wellhead growth became only 19 cm and 4 cm in Injector-1 and Injector-2, respectively. These remedial actions also led to restoring well and thermal integrity. Retrieved seal bore packer was sent back to manufacturer for appropriate failure analysis and providing useful feedback reports on the above issues. Monitoring and observation data along with failure analysis should provide vital information and possible improvement in completion strategy for steam injection wells that are planned for continuous steam flood projects in similar reservoirs.

No abstract

The study area is located in the south east of Abu Dhabi, covering approximately 4,000 km2. During several prospectivity studies carried out since 2012, high exploration potential was identified for Lower Cretaceous stratigraphic traps. To resolve the Aptian subtle trap configuration and lateral seals, it was decided in 2017 to acquire a 2,146 km2, high resolution 3D seismic cube. The paper will describe the planning, acquisition, processing and current interpretation results of this seismic campaign. Prior to the 3D seismic acquisition, a parameter design study was conducted to assess the requirements for the seismic acquisition and to insure that potential stratigraphic traps can be imaged in the newly planned 3D seismic cube. The processing was conducted on a zipper by zipper basis, allowing the processing of the acquired data while the remaining acquisition was still ongoing. It was conducted in a south to north direction, allowing the interpretation of the southern most zipper first which has greatest potential according to the existing prospectivety studies. Initial interpretation results confirm the challenge to interpret actual clinoform shapes at the Aptian level. Furthermore, multiples initially obstructed the seismic interpretation. Additional processing was carried out to reduce the impact of multiple energy on the seismic events. It was observed that noise reduction was acheived after the integration of each zipper, as the velocity model was further improved with each step. Albeit with these challenges, attribute extraction has been proven to be highly valuable in defining clinoform trends due to the high quality of the acquired seismic. Based on the seismic interpretation results, an exploration campaign to unlock the potential of the Aptian and deeper prospectivity in the East of the study area has been planned. For the first time in ADNOC and the emirate of Abu Dhabi, a 3D seismic survey was designed, acquired, processed and interpreted to target stratigraphic traps as the main objective. To accelerate the exploration campaign, the 3D seismic data was processed while the acquisition was ongoing. With this strategy, an 18-month turnaround from start of acquisition in December 2017 to the spud of first exploration well in May 2019 was achieved.