Factors Contributing to Fluid Loss During Wellbore Drilling and Formation Analysis
19 Jun,2020
What are the key factors that lead to formation leakage during wellbore drilling? First, what are the prerequisite conditions for formation leakage to occur?
Water well drill pipe Let’s analyze the factors contributing to formation fluid loss. First, what are the prerequisite conditions that must be present for such losses to occur?
① The formation contains pores, fractures, faults, or solution cavities that are interconnected, providing channels for mud to flow.
② The mud column pressure exceeds the pressure of liquids and gases in the formation.
③ When the mud column pressure and its lateral pressure exceed the formation's own fracture pressure, the formation fractures, leading to wellbore leakage.
Human factors
1. Improper handling leads to well leakage
⑴ Wellbore wall spalling and collapse can block the outer ring of the drill pipe, leading to formation leakage when pumping begins.
(2) The wellbore is unclean, with excessive cuttings and debris, leading to poor mud circulation, excessively high pump pressure, and eventual formation breakdown.
(3) The mud has a high specific gravity, high viscosity, and elevated shear strength. When the mud pressure exceeds the formation pore pressure, wellbore leakage occurs. In this situation, reducing the mud's specific gravity, viscosity, and shear strength will help stop the leak.
⑷ Mud packing around the drill bit or stabilizer, leading to increased pump pressure and formation leakage.
⑸ When the mud remains stationary in the well for more than 24 hours, it develops a strong network-like structural integrity. During drill string retrieval, instead of circulating in sections, the operation proceeds directly to the bottom of the well, resulting in high pump pressure when pumping begins—and ultimately leading to formation breakdown and loss circulation.
⑹ The mud pump's displacement cannot keep up, resulting in a large volume of cuttings inside the wellbore, increased pump pressure, and eventual formation breakdown.
⑺ Water well drill pipe The downhole drilling speed is too fast, resulting in excessively high surging pressure that fractures the formation.
⑻ Initially, the well experienced a loss circulation and a blowout. However, when attempting to increase the mud weight, the excessive mud density unexpectedly led to another loss circulation event.
2. There are pumping wells around the well site, which lower the groundwater level and reduce pore pressure, creating significant negative pressure. Once the drill penetrates the formation, substantial fluid loss is likely to occur.
3. During oil and gas extraction, the process causes groundwater levels to drop and pore pressures to decrease, creating significant negative pressure. Once the formation is penetrated by drilling, substantial fluid losses can occur.
4. Fracturing and acidizing increase fractures in the formation, while water injection for cleaning raises pore pressure within the formation—both of which can lead to wellbore leakage.
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