Shale play assets are exploited using horizontal wells in which measuring and controlling top-of-tool forces are necessary for positioning tools. Methods currently applied to deal with these forces are inefficient.
In traditional vertical wells, tool transportation relies on gravity force and simply unspools the wireline cable until the tool reaches target location. In horizontal wells, gravity is not enough to overcome friction; therefore, pumping fluid downhole or using a tractor is required to transport tools. Dynamic control of the transport rate is necessary because of the wide variation in friction forces along the tool path (attributed to well geometry), proppant settling between stage stimulations, changes or defects in casing, etc. Transport rate controls must help ensure the correct transportation force is applied. For pumping operations, this force should not be so low the tool stalls downhole, but not so high it results in a pump off and requires tool fishing with associated nonproductive time (NPT). For tractor jobs, it is important to get the tools to the target as quickly as possible without risking damage to the cable or stalling the tractor motion. Too little tension on the cable can cause drum crush in which tension loading differences between the run-in and pull-out tensions result in conductor damage; too much spooling off tension causes the tractor to stall. For wells with challenging geometries, dynamic adjustment of transport rate based on sensed cable tension and wireline speed has proven to be difficult. The tight coordination required to the wireline operator responsible for cable speed control adds to the challenge, and high risk of parting the cable or pump off of tools has been reported in these scenarios.
The authors developed a successful approach based on automation (feedback controls), which coordinates independent systems (wireline, pumping, or tractor) to improve the horizontal tool transport process. Field testing of this automated scheme is ongoing and has demonstrated its potential for improved run times, reduced risk, and cost savings for operators. This paper provides:
Description of the tool transport operation and architecture: sensors (including a key downhole tension sensor) and actuators (pumps), visualization, modeling, algorithm implementation, and tuning.
Field testing results: comparing runs in real wells vs. simulation results for the same wells, listing benefits and lessons learned based on the authors experiences with one operator.
Automation of the tool transport operation by linking downhole sensors to surface controls is novel in the industry. The paper describes in detail the proposed architecture and provides compelling field test results.