How to Use Double Stabilizers

The primary effect of double stabilizers lies in stabilizing the azimuth. In practice, we have found that in most cases, double stabilizers serve to stabilize or slightly increase the azimuth. Some drill string configurations can even result in significant increases in azimuth if used appropriately, without leading to a decrease in azimuth. Therefore, double stabilizers are used when the azimuth is just right or slightly smaller than desired. That is, when a strong trend toward azimuth reduction is observed, and further reduction would result in the azimuth being too small, it is crucial to promptly implement double stabilizers to stabilize the azimuth. If delayed, the opportunity will be lost once the survey points pass by.

In terms of stabilization, the closer the lower stabilizer is to the drill bit, the stronger its ability to increase the azimuth. When L1 exceeds 5 meters, the stabilizing effect diminishes significantly. Secondly, the smaller the distance between the two stabilizers, the stronger their azimuth stabilization ability. Additionally, the larger the outer diameter of the upper stabilizer, the stronger its azimuth stabilization ability. Generally speaking, the outer diameters of both stabilizers should not be less than 210 mm. As for the specific positions of the stabilizers, these should be determined based on the inclination needs. Below are some examples; please feel free to critique any inaccuracies.

  1. Strong Inclination Increase Combination This combination is a “classic” example of a double-stabilizer structure for increasing inclination, widely used across various teams, including Teams 2 and 3. Its configuration is: 8-1/2 Bit + double-female stabilizer (Φ213 and above) + one NDC + one DC + male-female stabilizer (Φ210 to 213). The key characteristic of this drill string is its significant inclination increase, capable of ensuring an increase rate of over 5°/100m, averaging around 7°/100m. It is an optimal choice when the outer diameter of the NDC is too large and the inclination does not rise sufficiently. The critical factor in its application is that the outer diameter of the lower stabilizer must be larger than that of the upper stabilizer; otherwise, it would function like a large pendulum reducing inclination. Typically, there is no need to add another connection below the lower stabilizer. If you need to reduce the inclination increase rate, other double-stabilizer structures should be considered. Strictly speaking, due to the distance between the stabilizers, this structure’s azimuth stabilization ability is not particularly strong. Adding a long connection below the lower stabilizer would further weaken its azimuth stabilization ability, negating the purpose of using double stabilizers.
  2. Weak Inclination Increase Combination This combination sacrifices part of the strong inclination increase capacity in favor of enhanced azimuth stabilization. Its structure is: 8-1/2 Bit + double-female stabilizer (Φ213 and above) + one NDC + one NDC + short drill collar (2 to 3 meters) + male-female stabilizer (Φ210 to 213). This combination is characterized by its strong inclination increase and azimuth stabilization. Even when faced with a strong trend toward azimuth reduction, inserting this combination can effectively curb the trend, with an increase rate of 2 to 4°/100m. This is a good combination for adjusting the inclination increase rate while forcibly stabilizing the azimuth. The critical factor remains that the outer diameters of the two stabilizers should be “larger below, smaller above,” and never the other way around. Additionally, the longer L2 is, the higher the inclination increase rate, with a minimum length of 12 meters. Short drill collars are difficult to omit—if you genuinely want to increase inclination. Based on actual needs, a short connection can be added below the lower stabilizer to adjust the inclination increase rate. The longer the connection, the lower the inclination increase rate, ideally within the range of 0 to 1 meter. Longer connections turn into inclination stabilization or even inclination reduction tools. Adding a short connection has little impact on the azimuth stabilization effect of the drill string.
  3. Inclination Stabilization Combination An inclination stabilization combination further sacrifices inclination increase capacity to achieve stronger azimuth stabilization. The structural forms vary, but they all evolve from the previously mentioned inclination increase combinations. 8-1/2 Bit + double-female stabilizer (Φ213 and above) + short drill collar (2 to 5 meters) + male-female stabilizer (Φ210 to 213). This structure is described in the <Drilling Manual (Operator)> and confirmed in Team 3’s research papers to have excellent inclination and azimuth stabilization effects. I believe this is the strongest azimuth stabilization effect among all double-stabilizer structures. The critical factor remains that the outer diameters of the two stabilizers should be “larger below, smaller above.” Similarly, connections can be added to adjust the distance between the two stabilizers to alter the inclination increase rate.

8-1/2 Bit + 430*410 (0.4 to 1.5 meters) + male-female stabilizer (Φ210 to 213) + one NDC + male-female stabilizer (Φ210 to 213). This structure also provides excellent azimuth stabilization effects, allowing the inclination increase rate to be adjusted by changing the length of the connecting joint. The longer the joint, the lower the inclination increase rate. By adjusting the outer diameters of the two stabilizers, the structure can be oriented toward inclination increase or reduction. Larger lower stabilizers favor inclination increase, while larger upper stabilizers favor inclination reduction. Therefore, the inclination increase rate of this structure can be flexibly controlled within ±3.5°/100m, indicating that the inclination increase rate is unstable, influenced by factors such as the outer diameter of the non-magnetic stabilizer, the length of the connecting joint, the formation, and drilling parameters. Thus, if experience is lacking, sufficient room should be left for subsequent inclination control, especially avoiding its use in the first inclination increase section. We have used this multiple times, and although the inclination adjustment sometimes falls short, the azimuth stabilization effect is always satisfactory (please refer to the attached table for specifics).

8-1/2 Bit + double-female stabilizer (Φ210 to 212) + one NDC + male-female stabilizer (Φ213). This structure connects the stabilizers in a “smaller below, larger above” configuration, achieving similar inclination and azimuth stabilization effects.

  1. Inclination Reduction Combination Adjusting the outer diameters of the stabilizers in the previous inclination stabilization structure to a “smaller below, larger above” configuration can achieve slight inclination reduction. Generally, the outer diameter of the lower stabilizer should be Φ210 to 211.5, and the upper stabilizer should be Φ213 and above.

Strong inclination reduction double-stabilizer structure: 8-1/2 Bit + 430*410 + short drill collar (over 2 meters) + male-female stabilizer (Φ210 to 213) + one NDC + male-female stabilizer (Φ210 to 213). This inclination reduction structure also provides good azimuth stabilization effects, with an inclination reduction rate of 8 to 12°/100m. Moving the two stabilizers upward also achieves strong inclination reduction, but the inclination reduction rate does not increase significantly, and the azimuth stabilization effect is greatly weakened, making it unnecessary to use this configuration.

Correct Usage of Double Stabilizers To correctly use double stabilizers, one must thoroughly understand the performance characteristics of the specific double-stabilizer structure and avoid misinterpretation. This year, the technology team issued a bulletin regarding the use of double stabilizers. Some teams experienced stabilization or even inclination reduction when using “double-female + NDC + male-female” for inclination increase. There were also instances where insufficient stabilizer outer diameters led to poor azimuth stabilization. Therefore, I believe:

  1. First, manage the purification and rock-carrying performance of the drilling fluid, ensuring smooth circulation and normal fluid flow rates to prevent downhole complexities.
  2. Accurately measure the outer diameters of the drill bit and stabilizers before drilling to ensure their outer diameters do not exceed the original borehole size and that the stabilizer outer diameters are smaller than the drill bit outer diameter. Some old or even new drill bits may have too small outer diameters, while new stabilizers or transition stabilizers may have too large outer diameters, leading to drilling difficulties or stuck drill strings during tripping out.
  3. Ensure accurate positioning of the two stabilizers during drilling. Engineers should personally supervise the operation to prevent accidental errors, such as reversing the positions of the stabilizers or using stabilizers of the wrong size, which could turn intended inclination increase into inclination reduction.
  4. Implement the measure of reaming twice after each drill stem is added to further correct the borehole.
  5. In soft formations, try to minimize jet impact to prevent excessive borehole erosion, which could increase the gap between the lower stabilizer and the borehole wall, weakening the inclination increase effect.

Conclusion

  1. The “strong inclination increase and azimuth stabilization” control method benefits azimuth control and helps improve average mechanical drilling speed.
  2. Double stabilizer structures offer excellent azimuth stabilization effects and can meet the requirements of inclination control.
  3. To achieve expected results, it is essential to correctly understand and apply double stabilizers.