Research on the Determination Method of Additional Safety Factor Margin for Ultradeep Well Pipe Strings under...

Area of Science:

• Petroleum Engineering
• Geomechanics
• Materials Science

Background:

• Ultradeep oil and gas well fracturing presents unique challenges due to complex operational stresses on pipe strings.
• Current pipe string design methods lack accurate prediction of multisource loads, leading to suboptimal safety margins and inefficient reservoir stimulation.
• There is a critical need for refined safety verification methods based on quantitative load characterization for ultradeep well development.

Purpose of the Study:

• To develop theoretical calculation methods for loads experienced by pipe strings during complex fracturing operations in ultradeep wells.
• To establish numerical models for predicting additional stresses (water hammer, vibration, collision) in pipe strings.
• To propose a method for determining the design margin of the pipe string safety factor based on maximum cumulative stress.

Main Methods:

• Development of numerical models to solve for three types of additional stresses in the pipe string during ultradeep well fracturing.
• Theoretical calculation of loads under complex fracturing conditions.
• Case study analysis using data from a well in the Junggar Basin, Xinjiang, to calculate load fluctuations and safety factor margins under varying operational parameters.
• Derivation of required additional safety factor design margins based on maximum cumulative stress.

Main Results:

• Extended fracturing pump operation cycles significantly reduce total additional load and safety factor margins.
• Altering pipe segment length ratios impacts different stress types: reducing large-diameter segments mitigates water hammer but increases vibration and collision loads.
• Calculated safety factor margins varied between 0.262 and 0.392 across different pipe segment length ratios.
• A decrease in pump cycle from 0.625s to 1.875s reduced total additional load by 53% and safety factor margin from 0.262 to -0.244.

Conclusions:

• The proposed theoretical calculation and numerical modeling approach provides a refined method for characterizing multisource loads on pipe strings in ultradeep wells.
• The study highlights the significant impact of operational parameters (pump cycle, pipe segment length) on pipe string stress and safety factor margins.
• Findings offer crucial theoretical guidance for optimizing the design and enhancing the safety verification of pipe strings in demanding ultradeep oil and gas exploration and production.