Shell Exploration (China) Ltd had used motor and measurements-while-drilling (MWD) to drill dual-lateral wells in tight gas reservoirs with 15 m average thickness in the Changbei block of China's Changqing field for 7 years. The development had recently moved toward a marginal thin target reservoir in the flank area. Well placement was expected to be a challenge because the target was only about 1.5 m thick and because structural and stratigraphic uncertainty was high due to the sand body being poorly connected and interbedded with clay. Drilling efficiency also posed a challenge—high ROP in the very hard, abrasive formation would be difficult to achieve.
An integrated solution incorporating the expertise and technologies of SLB enabled Shell not only to successfully place the well within the thin target reservoir but to significantly improve drilling efficiency compared with performance on previous wells. The integrated solution teamed a PowerDrive X6 RSS with an 8 1/2-in Gemini GF65 roller cone bit certified for this application by simulation with the IDEAS integrated drillbit design platform.
This RSS-bit combination provided a faster average ROP than the mud motors used in previous wells, at much lower bit rotation speeds, as well as better trajectory control that delivered a smoother wellbore. In addition to eliminating sliding, use of the PowerDrive X6 RSS instead of a mud motor reduced nondrilling time an average of 5 hours per day—from 6 hours to 1 hour— and substantially increased run length.
Well placement in the thin reservoir was optimized using geoVISION fullbore real-time, highresolution resistivity and gamma ray images to evaluate structural dips and stratigraphic events, as well as near-bit direction and inclination (D&I) measurements to steer the RSS and keep the trajectory within a small window. High-resolution resistivity images from geoVISION service helped the team determine that the target reservoir had a structural updip rather than the downdip indicated in the predrill model. This enabled the team to adjust the trajectory to avoid exiting the reservoir.
The fit-for-purpose integrated solution and multidisciplinary teamwork resulted in optimal well placement within the 1.5 -m target reservoir and saved Shell more than 25 days and USD 1.3 million off AFE. On its first run, the BHA with the PowerDrive X6 RSS and optimized Gemini roller cone bit set a new Changbei project record for a single run, drilling 548 m in 105 drilling hours. That more than doubled the 210 m and 49 drilling hours per run averaged with mud motor BHAs in previous Changbei wells, and saved more than 2 days. Furthermore, the thin gas reservoir has produced at the rate of 1.2 million m3/d—double the production goal for the well. Shell plans to continue using RSS and LWD BHAs, optimized drill bits, and well placement services in its Changbei horizontal well campaign.
