There are two essentially different types of inclination-only tools in current use. The simple MD TOTCO deviation survey tool (single shot) so, called after its manufacturer, and the slightly sophisticated Teledrift style of tool.
A Totco ring is not really a drilling sub. We place a small insert inside the drill string between a pin and a box connection. It does not interfere with the connection. In addition, it does not significantly restrict fluid flow down the string. Generally, Totco does act as a trap for directional surveying tools that we drop from the surface. We can also retrieve it later after tripping the string out from the hole. When including a Totco ring in the bottom hole assembly, we must consider internal access for balls and darts.
Totco Survey Tool Mechanism
MD Totco Style inclinometers are the most basic type of deviation survey tool (deviation control). The mechanism consists of a pendulum, with a stylus attached and a disk of paper which the stylus penetrates when taking the survey. This action will mark the paper with concentric rings indicating the hole inclination.
Dropping the instrument in a protective barrel down the drill string will make it land on a baffle plate in the Totco ring. Set the mechanical timer on the surface to ensure taking the survey after landing the tool. Furthermore, we can run the tool on a wireline.
The driller usually runs the single-shot MD Totco survey tool. The pre-survey checklist and running procedure are given below. (When using a magnetic single-shot tool for inclination-only surveys
follow the running procedure for MSS.)
- Check that the instrument landing assembly will seat correctly in the landing ring (Totco ring), not jam or land eccentrically.
- Install the landing ring in the proper place when making up the BHA.
- Avoid landing the instrument directly on the top of the drilling bit, mud motor, or turbine. The instrument could get stuck (stuck pipe problem) and make circulation impossible.
- Check that the fishing tool will fit over the fishing neck.
- Check that the instrument will pass the BHA above the landing ring and not hang up (e.g., in the drilling jar).
- Check that the instrument kit box is complete and the angle units have been checked in the workshop before delivery to the healthy site. Check that no angle unit has been used more than 25 times after calibration.
- Use sinker bars if the drilling fluid has a high density and is viscous.
- Before directional drilling surveying, circulate sufficiently to avoid backflow of cuttings into the BHA.
- Estimate the time-lapse. This should be equal to the sum of the times required to:
- mount the instrument in the barrel
- run the instrument through the drill string
- provide a safety margin of a few minutes (3-5 minutes) in case of any delays.