A major challenge in horizontal directional drilling (HDD) is controlling fluid loss. It has been estimated that fluid loss during HDD operations can be as high as 30% of the total pumped volume if left uncontrolled. This represents a significant opportunity for improvement, especially when considering the cost of hydraulic fracturing fluids and the risks associated with inefficient use of these expensive fluids.
Fluid loss not only wastes expensive drilling fluid but also quickly creates a low-pressure zone behind the drill string. This instigates two undesirable conditions:
1. Mud returns from high permeability formations, mixing with the drilling fluid and contaminating it, or mixes into an open borehole error that has been left unattended without a kill operation.
2. Low-pressure zones around the outside of the drill string cause a reduction in the cross-sectional area of the borehole. This portion of the hole, now too small to continue supporting drilling, collapses into a frictionless space known as a “kicked string.”
Both conditions increase risk and shorten HDD runs. In extreme cases, they can completely halt operations in an hdd crossing.
During the life of any horizontal directional drilling (HDD) contract, many complications can arise that will affect the profitability and efficiency of the entire project. One possible complication is controlling fluid loss in HDD operations. When fluid is lost out of the annulus between the drill string and the borehole, several problems can arise:
- A controlled HDD is easier to steer, creating an accurate borehole.
- A controlled HDD also results in the use of less expensive drilling fluid.
Controlling fluid loss is greatly impacted by mud weight (density), especially when drilling through unconsolidated formations like soils and soft clays. A mud with a high density will have the tendency to retain particles of the formation as it passes through the drill bit. In contrast, mud with a low density will have lower retentivity and smaller particle size. It will therefore lose fewer particles out of the annulus.
Uncontrolled or lost fluid can have significant ramifications that could cost thousands of dollars in repairs and equipment damage. The lost drilling fluid can seep into the ground, causing environmental concerns. The fluid loss could also result in rig downtime, or even render casing unserviceable for future use.
Fluid loss control is vital in every hdd crossing operation and should be one of the top priorities when preparing a drilling plan. The following are key steps to controlling fluid loss during HDD operations:
- Use appropriate weighting agents for the formation being drilled to create a more dense drilling fluid.
- Perform regular mud checks for density, colour, turbidity, and pH levels to identify any potential problems with the quality of the drilling fluid.
- Remove cuttings from the borehole as often as possible.
- Ensure that the flow rate of the drilling fluid is not too high or low based on the diameter of the wellbore. If the flow rate is too high, it can cause fluid loss into the formation and carry dirt and rock cuttings back to the surface.
Controlling fluid loss during HDD operations is critical to the borehole’s overall integrity and maintaining cost-effective drilling practices. If fluid loss problems arise during HDD operations, they can be addressed immediately with proper remediation tools and techniques. Prompt actions prevent further damage and costly repairs in the future.