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Changning shale gas block is located in the southern part of the Sichuan basin. It is one of the first pilot experimental shale gas blocks in China. The paper will elaborate the drilling challenges in the field and the overall drilling performance with conventional approaches. In 2014, new drilling tools and methods were tried and applied. These significantly improved the performance, further elevating the drilling speed to a new level.The paper will review the drilling performance of horizontal wells completed previously in the field. It will focus on demonstrating formation characteristics, well trajectory and geometry design, drill bit and directional bottomhole assembly (BHA). One of the biggest challenges is the hard rock on top of the shale formation that constrains the drilling speed, especially when designing the curve interval at the hard rock. By analyzing the drilling challenges, a new drilling system and method were introduced to the project in 2014 to combat the challenges. It has been proven successfully with actual drilling data.Initially, as a pilot project, conventional motor technology was applied to six horizontal wells in Changning block. The average well drilling cycle was approximately 66 days for 1000 m of lateral section. The main challenge with motor drilling was high drag at the curve and lateral due to extreme friction as high mud weight was applied to balance the formation stability. This resulted in a poor on-bottom penetration rate during sliding mode. Directional work at the hard rock formation posed an additional challenge. In early 2014, a hybrid high-build-rate rotary system was applied to deepen the kickoff point and avoid the steering work in the hard zone. Air drilling was used to drill vertically across the hard rock. A power rotary steering system was also implemented to further improve the drilling speed in the lateral section. The combination of technical approaches led to significant drilling improvement. The rate of penetration (ROP) on bottom at the curve section has improved 200% over conventional drilling. The well drilling cycle was cut in half, which was considered as a breakthrough achievement in the field.With the application of hybrid high-build-rate rotary steering system, the new well design can be executed. Air drilling is chosen to drill through the hard rock in the shortest distance. Using the power rotary steering system for the lateral further promotes the drilling performance to a new level.
Changning shale gas block is located in the southern part of the Sichuan basin. It is one of the first pilot experimental shale gas blocks in China. The paper will elaborate the drilling challenges in the field and the overall drilling performance with conventional approaches. In 2014, new drilling tools and methods were tried and applied. These significantly improved the performance, further elevating the drilling speed to a new level.The paper will review the drilling performance of horizontal wells completed previously in the field. It will focus on demonstrating formation characteristics, well trajectory and geometry design, drill bit and directional bottomhole assembly (BHA). One of the biggest challenges is the hard rock on top of the shale formation that constrains the drilling speed, especially when designing the curve interval at the hard rock. By analyzing the drilling challenges, a new drilling system and method were introduced to the project in 2014 to combat the challenges. It has been proven successfully with actual drilling data.Initially, as a pilot project, conventional motor technology was applied to six horizontal wells in Changning block. The average well drilling cycle was approximately 66 days for 1000 m of lateral section. The main challenge with motor drilling was high drag at the curve and lateral due to extreme friction as high mud weight was applied to balance the formation stability. This resulted in a poor on-bottom penetration rate during sliding mode. Directional work at the hard rock formation posed an additional challenge. In early 2014, a hybrid high-build-rate rotary system was applied to deepen the kickoff point and avoid the steering work in the hard zone. Air drilling was used to drill vertically across the hard rock. A power rotary steering system was also implemented to further improve the drilling speed in the lateral section. The combination of technical approaches led to significant drilling improvement. The rate of penetration (ROP) on bottom at the curve section has improved 200% over conventional drilling. The well drilling cycle was cut in half, which was considered as a breakthrough achievement in the field.With the application of hybrid high-build-rate rotary steering system, the new well design can be executed. Air drilling is chosen to drill through the hard rock in the shortest distance. Using the power rotary steering system for the lateral further promotes the drilling performance to a new level.
An exploration well was commissioned to evaluate a potential tight gas reservoir by drilling a combined curve and horizontal section while facing a narrow mud weight window (NMWW). Positioned below an anomalous formation, a high probability of influx, losses and stuck pipe scenarios prevailed, coupled with a very low ROP scenario. Also, being a rather long combined curve and lateral section, there was a high risk of caving after drilling, which could disrupt running the liner. To land the well on target without having any undesirable effects, it was critical to maintaining correct pressure profiles not only during drilling but also during tripping and setting/cementing the liner. A thorough hydraulics analysis and carefully executed MPD design were used to maintain a constant bottom-hole pressure during drilling, connections, and tripping. The MPD system was fully capable of recognizing drilling parameters in real time and adjust surface pressure accordingly. This allowed the 5-7/8 in. section to be drilled using the lowest possible mud weight while attaining the necessary overbalance. The lateral section was successfully completed to improve the stipulated timeline. This was attributable to ROP improvement by 29% and also to 164% footage drilling enhancement per bit run, which allowed the drilling team to finish the 5 7/8 in. hole section in record time compared to the offset wells. By using correct mud formulations and accurate wellbore pressure mapping, there was no loss while drilling the section; and the Early Kick Detection module was successfully deployed to accurately monitor influxes. Whenever a discrepancy was observed between the flow in/out, the MPD system was fine-tuned to adjust the pressure profile to match the two flows. Following drilling, the wash-down LWD was utilized with MPD and low mud weight. The liner was run and set, while the hole was filled with a low weight mud, using the MPD system. There were no tight spots or caving observed in the whole run and the liner was able to reach the bottom with no issues. A detailed paper would discuss the in-depth technical analysis of this case history.
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