Seeing the RSS Response Near the Bit
- Chris Ely
- Jul 28
- 7 min read
Field Performance of Continuous Inclination and Azimuthal Gamma 16 ft Behind the Bit
Rotary steerable systems provide precise control of wellbore trajectory, but the quality of a steering decision ultimately depends on how quickly the Directional Driller can determine what the bit and lower BHA are actually doing. During a recent field deployment, MWD-DDT evaluated a different approach.
An At-Bit measurement system was positioned directly above a standalone Rotary Steerable System, with the At-Bit sensors located approximately 16 ft behind the bit. The RSS operated independently and was not connected to the conventional MWD system.
The At-Bit system provided two measurements particularly valuable to the Directional Driller:
Continuous Inclination for near-bit trajectory response, and Azimuthal Gamma Ray for high-density formation information close to the bit.
The resulting dataset demonstrates the operational value of moving critical measurements significantly closer to the drilling action.
A Standalone RSS Application
The BHA configuration is an important part of the case study.
The RSS was operated in standalone mode. Steering commands and mode selections were made by the Directional Drillers based on the drilling objective and available information rather than through an integrated RSS/MWD measurement platform.
Above the RSS, the MWD-DDT At-Bit system independently acquired Continuous Inclination and Azimuthal Gamma Ray measurements.
This created a valuable measurement architecture:
RSS → At-Bit Measurements → Conventional MWD
The At-Bit sensor location was approximately 16 ft behind the bit, while the conventional MWD directional sensor was approximately 84 ft behind the bit.
That represents approximately 68 ft of physical measurement-location advantage for inclination information.
The importance of that difference becomes clear when steering decisions are being made in a narrow TVD window.
Continuous Inclination Close to the Bit
Conventional surveys remain essential for definitive wellbore positioning. However, their measurement location necessarily means that the bit has already drilled beyond the point being surveyed.
Continuous Inclination provides something different.
It gives the Directional Driller an indication of trajectory behavior much closer to the bit.
During Run 28, At-Bit Continuous Inclination was compared against the inclination response subsequently measured by the conventional MWD system.
The independently observed spatial relationship between the two measurements was approximately 69 ft.
The known physical separation between the sensors was approximately 68 ft.
That agreement is significant.
It demonstrates that trajectory features observed by the At-Bit inclination measurement subsequently appeared in the conventional MWD measurement at almost exactly the distance expected from the BHA geometry.
In practical terms, the two independent measurements were seeing the same borehole trajectory from two different locations in the BHA.
From Steering Decision to Measured Response
The more compelling operational result came from correlating the Directional Drillers' documented RSS mode selections and downlinks with the At-Bit inclination response.
Because the RSS was standalone, the At-Bit system was not receiving steering information electronically from the RSS.
It simply measured what happened.
The Directional Drillers documented their RSS commands, set modes and associated depths in their daily reports. Those events could then be compared with the At-Bit memory and Continuous Inclination data.
In key portions of the run, the effect of a steering-mode decision became identifiable in the near-bit inclination trend after only approximately 18 ft of additional drilling.
That is an important distinction.
The At-Bit tool was not predicting what the RSS should do.
It was independently measuring what the borehole was actually doing after the steering decision.
For a sensor located approximately 16 ft behind the bit, seeing a recognizable response after roughly 18 ft of drilling places the measurement extremely close to the point where the new borehole trajectory was being created.
Closing the Feedback Loop for the Directional Driller
Consider the conventional steering workflow.
A Directional Driller selects an RSS mode or steering setting. The BHA drills ahead. The directional measurement eventually reaches the newly drilled interval. The response is evaluated, and another decision is made.
The farther the directional sensor is from the bit, the more footage must be drilled before that feedback becomes available.
Near-bit Continuous Inclination shortens that feedback distance.
During this run, the Directional Driller could use the At-Bit measurement to evaluate whether the trajectory was beginning to respond to the selected RSS mode without waiting for the conventional MWD measurement location to reach the same section of borehole.
That capability becomes particularly valuable when maintaining a narrow TVD target.
Instead of asking:
"What did the BHA do 84 ft behind the bit?"
the drilling team gains another question:
"What is the trajectory doing approximately 16 ft behind the bit?"
That difference can materially change the timing of a steering decision.
Independent Measurement Above a Standalone RSS
Another important aspect of the deployment is independence.
The At-Bit system did not depend on the RSS for its inclination measurement.
The RSS did not need to communicate its steering mode to the MWD system for the At-Bit tool to identify the resulting trajectory response.
The At-Bit measurement package effectively acted as an independent observer of RSS performance near the bit.
This has implications beyond this specific application.
It means near-bit inclination can potentially provide a common measurement layer across different steering technologies and BHA configurations, including applications where direct integration between the RSS and MWD platform is unavailable or undesirable.
Azimuthal Gamma 16 ft Behind the Bit
Continuous Inclination addressed the directional side of the application.
Azimuthal Gamma Ray provided the formation measurement.
The At-Bit system acquired high-density gamma measurements from approximately the same near-bit location, only 16 ft behind the bit.
This means the Directional Driller was not limited to knowing how the trajectory was responding.
The system also provided information about what the bit was drilling through.
Azimuthal Gamma adds directional context to conventional gamma measurements by resolving formation response around the circumference of the borehole.
For geosteering and well placement, the combination is particularly valuable:
Near-bit Continuous Inclination identifies how the trajectory is changing.
Near-bit Azimuthal Gamma identifies changes in formation response around the wellbore.
Both measurements are being made close to where the drilling decision is actually taking effect.
Measurement Density Matters
Near-bit placement alone is not enough.
For the information to be operationally useful, measurements must also be sufficiently dense to identify changes over short drilling intervals.
The run demonstrated continuous inclination tracking and high-density azimuthal gamma acquisition throughout the RSS application.
That density becomes important when the objective is not simply to reconstruct the well after drilling, but to recognize changes while there is still an opportunity to respond.
A formation change or directional trend occurring over tens of feet can be substantially more actionable when the sensor is 16 ft behind the bit rather than more than 80 ft behind it.
Two Measurements, One Near-Bit Picture
The significance of the application is ultimately the combination of the measurements.
Continuous Inclination answers:
Where is the trajectory going?
Azimuthal Gamma helps answer:
What is the formation doing around it?
And both measurements are acquired approximately 16 ft behind the bit.
For a Directional Driller operating a standalone RSS, that provides an independent near-bit picture of both trajectory response and formation response.
A steering mode can be selected.
The BHA can drill ahead.
The resulting inclination behavior can begin to become identifiable after a relatively short interval—in key examples from Run 28, approximately 18 ft of drilling.
And the gamma measurement provides formation context from essentially the same near-bit region.
That begins to close the distance between decision, response and measurement.
Validating the Data
For near-bit information to influence a steering decision, the Directional Driller must be able to trust it.
The run provided an important validation opportunity because the At-Bit Continuous Inclination measurement could be compared with the conventional MWD inclination measurement after the MWD sensor reached the same section of borehole.
The result was compelling:
Physical sensor separation: ~68 ft
Observed inclination-pattern displacement: ~69 ft
The agreement provides independent evidence that the At-Bit system was identifying real trajectory behavior rather than simply producing a short-term directional indication.
The conventional measurement subsequently confirmed the response at approximately the location predicted by the BHA geometry.
That is what transforms Continuous Inclination from an additional data channel into a potentially useful steering aid.
Why This Matters for Well Placement
In a large target window, waiting another 60 or 70 ft for directional confirmation may be manageable.
In a narrow TVD window, that distance matters.
A Directional Driller needs to know not only where the well has been, but how the trajectory is responding to the current steering decision.
Near-bit Continuous Inclination provides earlier visibility into that response.
Azimuthal Gamma provides near-bit formation context.
Together, they give the drilling team information much closer to the decision point.
The objective is not to replace conventional surveys.
It is to reduce the informational distance between the bit, the formation and the Directional Driller.
Run Performance Summary
This run demonstrated a unique configuration in which an MWD-DDT At-Bit measurement package operated directly above a standalone RSS without requiring integration between the RSS and conventional MWD platform.
The field results demonstrated:
Continuous Inclination approximately 16 ft behind the bit
Azimuthal Gamma approximately 16 ft behind the bit
Approximately 68 ft measurement-location advantage relative to the conventional MWD directional sensor
An independently observed inclination displacement of approximately 69 ft, closely matching physical BHA geometry
Identification of trajectory response following documented RSS steering decisions after approximately 18 ft of drilling in key events
Independent measurement of RSS trajectory response without electronic integration with the RSS
High-density near-bit formation and directional information available from the same measurement package
The significance is not simply that measurements were made closer to the bit.
It is that those measurements provided information the Directional Driller could use to understand what the RSS was actually doing while the next section of wellbore was being created.
Measure the Response, Not Just the Command
A steering command represents what the drilling team wants the BHA to do.
The resulting wellbore represents what the BHA actually did.
The closer those two can be connected through measurement, the more informed the next steering decision can become.
This run demonstrated that Continuous Inclination and Azimuthal Gamma measurements approximately 16 ft behind the bit can provide that near-bit visibility even when operating above a standalone RSS with no direct RSS-to-MWD integration.
In key steering events, meaningful trajectory response became identifiable after only approximately 18 ft of drilling.
For directional drilling and geosteering applications where feet matter, 68 ft of earlier measurement location can matter even more.
MWD Downhole Drilling Tools LP
DRILL HARD. MEASURE EVERYTHING.
Comments