What Causes Poor Well Drilling Efficiency? Unveiling Three Key Factors Affecting Drilling Speed

What Causes Poor Well Drilling Efficiency? Unveiling Three Key Factors Affecting Drilling Speed

Factor 1: Unknown Subsurface Conditions – The “Inherent Resistance” of Geological Conditions

This is the most fundamental and also the most difficult factor to control. The complex and ever-changing subsurface conditions are the “first hurdle” to efficiency.

Rock Hardness and Drillability: Drilling in soft sand is naturally dozens of times faster than drilling in hard granite. This is an unchangeable objective fact.

Complexity of Formation Structure:

“Soft on top, hard below” interlayers: When the drill bit enters hard rock from soft rock, it is prone to “jumping” and deviation, requiring a slowdown in parameters, resulting in a sharp drop in efficiency.

Fractured Zones and Loss Zones: Developed formation fractures can lead to significant loss of drilling fluid (mud or water). Drilling fluid is not only responsible for cooling the drill bit and carrying cuttings, but more importantly, for stabilizing the wellbore. Once lost, the risk of wellbore instability increases significantly, requiring drilling to be stopped to address the loss, severely slowing down progress.

Clay Formations: In clay layers, drill bits are prone to "mud clogging," where clay adheres to the drill bit's cutting tools, forming a mud pad that prevents the drill bit from effectively contacting and cutting into new formations, resulting in idling and no progress.

Solution: Conduct detailed geological surveys before drilling to ensure thorough understanding of the formation. Prepare appropriate drilling tools and drilling fluid plans in advance based on the predicted formation.

Factor Two: Inappropriate Tools – "Acquired Inadequacy" of Drilling Rig and Tools

"A skilled craftsman must first sharpen his tools." Choosing incompatible or poorly functioning equipment is a fatal flaw in efficiency.

Mismatched Drilling Rig Capacity:

"Small horse pulling a large cart": Using a drilling rig with low torque and low feed pressure to drill hard rock will inevitably result in slow progress and significant damage to the equipment.

Incorrect Method Selection: Using a rotary drilling rig suitable for soft soil in hard rock formations is far less efficient than using a dedicated down-the-hole hammer or roller cone bit.

Incorrect Drill Bit Selection: Drill bits are designed for specific formations. Using a scraper bit designed for soft soil to drill hard rock will render it unusable within minutes; however, using a PDC or roller cone bit designed for hard rock can provide continuous and efficient rock breaking.

Inappropriate Drill String Assembly: The combination of drill pipes, drill collars, etc., downhole not only transmits power but also affects wellbore quality. An inappropriate assembly can easily lead to well deviation, wasting a lot of time correcting it.

Equipment Performance Degradation: Older drilling rigs, insufficient hydraulic system pressure, and reduced engine power will all result in weak output, naturally hindering drilling speed.

Solutions: Scientifically select the drilling method and rig model based on formation conditions, and equip different formations with "dedicated" drill bits. Strengthen equipment maintenance to ensure it is always in good condition.

Factor Three: Inaccurate Operation—The "Human Bottleneck" of Process Parameters

Even with the best equipment and a clear geological report, the final operation and decision-making are the "final step" in converting potential into efficiency.

Inappropriate Drilling Parameters: Mismatch between WOB and RPM: This is a core operational issue. In soft rock, a "high drilling speed, low drilling pressure" approach is recommended, while in hard rock, a "high drilling pressure, low drilling speed" approach is necessary. Incorrect parameter settings can lead to low efficiency or even damage to the drill string.

Improper pump flow rate and pressure: The drilling pump's flow rate determines the cuttings carrying capacity and the cleanliness of the wellbore. Insufficient flow rate results in repeated cuttings breakage at the wellbore, a phenomenon known as "repeated cutting," severely impacting the drilling speed.

Poor drilling fluid performance: Drilling fluid is the "blood" of drilling. Excessively high or low viscosity, or excessive solids content, will affect cuttings carrying capacity and wall protection, indirectly slowing down the drilling speed.

Operator proficiency and coordination: An experienced driller can keenly assess downhole conditions through instrument parameters and equipment sounds, making timely adjustments. The proficiency in auxiliary operations such as connecting and disconnecting drill pipe directly affects the percentage of pure drilling time.

Frequent well accidents: Accidents such as stuck pipe and broken drill string can take hours or even days to handle, posing a fatal blow to overall efficiency. Most of these accidents are related to improper operation and misjudgment.

Countermeasures: Optimize parameters using automated drilling systems, or strengthen driller training to improve their ability to adjust parameters based on real-time conditions. Strictly adhere to operating procedures to avoid accidents caused by human error.

Summary: Poor drilling efficiency stems from shortcomings in one or more aspects:

High underground resistance (geology) -> Inherent deficiencies, requiring compensation through anticipation and preparation.

Dull equipment (equipment) -> Acquired incompatibility, requiring correct selection and maintenance.

Disorganized on-site command (operation) -> Human bottleneck, requiring optimization through experience, technology, and meticulous management.

Therefore, improving drilling speed is a systematic project requiring efficient collaboration among geology, equipment, and processes; none can be neglected.