Applications

 

Below there are examples of real results of surveying the trajectory of wellbores, which helped our Customers reduce the risks of wellbore collision or determine the reasons for the low efficiency of hydrocarbon recovery and develop corrective measures. The following examples show the relevance of the problems of MWD measurements. 

 

1. Western Siberia, Russian Federation

DESCRIPTION:

Drilling a deviated well was performed beyond the Arctic Circle. The maximum inclination is 68 degrees, the measured depth is 4800 m. After drilling a section of the production casing, a logging was carried out, which showed a difference in azimuth of 2-3 degrees in the interval of 2000-2700 m between the magnetic survey tool and the MWD. The Customer decided to continue drilling based on the MWD data. After completion of the drilling, a survey was carried out with a drop gyro.

SURVEY RESULTS:

Measurements of a high-precision gyro showed a significant deviation of the well trajectory from the plan. Due to the difference in azimuth readings in the horizontal plane, a deviation is observed – the gyro survey at measured depth (MD) of 4760 m shows a difference in 152 m to the south relative to the MWD measurement. The fact of the deviation was admitted by the MWD contractor. The reason of the deviation lies in the problems of drilling at high latitudes – magnetic interference.

drop gyro Atlas Drilling

2. Sakhalin Island, Russian Federation

DESCRIPTION:

During the development of the offshore project, survey measurements were made with a gyro survey tool in the producing well. The purpose of the measurements is to clarify the spatial position of the drilled wells in order to avoid the risk of collision while drilling new wellbores. On a well with MD 6199 m and a maximum inclination of 84 degrees, a high-precision gyro survey tool was used.

SURVEY RESULTS:

The gyro survey has showed a difference in azimuth of 4-5 degrees with the MWD. The deviation of the well trajectory was 408 meters to the south relative to the MWD measurement. The reason for the discrepancy is magnetic interference, which significantly affects when drilling in the west-east direction.

drop gyro Atlas Drilling
drop gyro Atlas Drilling

3. Western Siberia, Russian Federation

DESCRIPTION:

During drilling a section of the production casing, LWD revealed a gas-oil contact (GOC) 15 meters higher (in vertical depth) relative to the drilling plan. The customer made a decision to stop drilling, retrieve the BHA and perform a control measurement with a drop gyro while pulling out the BHA.

SURVEY RESULTS:

High-precision gyro drop survey showed a significant deviation of the wellbore trajectory from the plan – a difference in true vertical depth (TVD) of 16 meters. The reason is the skipping of a drill stand by MWD operator in the interval 650-700 m. The fact of the deviation was admitted by the MWD contractor. The reason is in the problem of quality management and depth control.

4. Western Siberia, Russian Federation

DESCRIPTION:

During drilling a section of the production casing of horizontal well (MD 4046 m) Customer have decided to perform a control survey with a drop gyro. Drilling was carried out in magnetic West direction.

SURVEY RESULTS:

High-precision gyro drop survey showed a significant deviation of the wellbore trajectory from the plan of more than 100 meters – out of tolerance. Customer decided to re-check the survey with backup tool. New survey confirmed the first measurement and the fact that the trajectory deviated from the plan by 102 meters as a result of a difference in azimuth of 3 degrees. The fact of the deviation was admitted by the MWD contractor. The reason for the deviation lies in the magnetic interference when drilling in the west-east direction. Further drilling was tied to the gyro survey data.

сбрасываемый гироскоп Атлас

5. Western Siberia, Russian Federation

DESCRIPTION:

Control survey of deviated well by drop gyro after drilling of production casing section (MD 3050 m).

SURVEY RESULTS:

The measurement with a high-precision drop gyro revealed significant discrepancies in the horizontal plane at the bottomhole – more than 70 m. The reason for such a large measurement difference is the error in azimuth. The well was drilled in the most inconvenient direction, when even a slight magnetization of the BHA elements has a strong effect on the azimuth readings: up to a depth of 1400 m, a stable difference of almost 4 degrees is observed, then (after changing the BHA) there is a decrease in this difference to two degrees, and closer to the bottom, with the turn of the azimuth to the North, the influence of magnetization decreases and the difference in azimuth practically disappears.

6. East Siberia, Russian Federation

DESCRIPTION:

Checking the trajectory of the horizontal well, in which gas breakthroughs were observed, which negatively affected its flow rate.

SURVEY RESULTS:

Measurement with a high-precision drop gyro revealed discrepancies in the vertical plane – the borehole was located higher with a possible entry into the GOC. This helped make decisions to correct the trajectory to avoid financial and geological risks.

drop gyro Atlas Drilling

7. Western Siberia, Russian Federation

DESCRIPTION:

After drilling a horizontal well, according to MWD data, the lower part of the borehole is located above the oil-water contact (OWC). However, the actual well water cut is >80%. Similar problems were observed in adjacent drilled wells, which produced water cuts of more than 30% immediately after production start. The Customer decided to conduct a control measurement of the trajectory with a high-precision gyro.

SURVEY RESULTS:

Measurement with a high-precision drop gyro revealed discrepancies in the vertical plane in the lower part of the horizontal wellbore – more than 3 m. Taking into account the ellipses of uncertainty, the borehole entry under the OWC is possible. Possible reasons for the deviation of the wellbore into the water: an error in calculation of BHA sag (which is a critical factor when drilling horizontal wellbores), errors in measuring inclination (washouts, instrumental error), error in depth control. If a control survey were made on the production casing section with a drop gyro, the vertical depth error could be detected before drilling the productive horizon. This would help to take measures to correct the trajectory and avoid financial losses.

CONCLUSIONS

During the development of a oilfield, situations may arise when the next drilled well shows a lower productivity than previously drilled adjacent wells, although according to the geological model there are no conditions for this. In cases when an Operator receives a water cut higher than predicted in horizontal well, a high gas content or a low flow rate, it makes sense to check the actual wellbore trajectory to compare with the plan. 

For the producing wells, which are already cased by metal casing, only inclination can be measured with a magnetic survey tool. And if the well is highly deviated with an inclination exceeding 40-50 degrees, or horizontal, the wireline contractor will need to use expensive additional equipment, such as a downhole tractor, to recheck the trajectory. The cost of survey in this case increases significantly. 

The solution in such situations is to use a high-precision drop gyro survey tool, which will allow you to clarify the spatial position of the wellbore, even cased with steel casing, without the use of additional deployment means.