Calculation Model for Stick-Slip Deformation in Weak Horizontal Structural Surface Formation after Water Inflow

Area of Science:

• Geomechanics
• Reservoir Engineering
• Petroleum Geology

Background:

• Weak horizontal structural surfaces in reservoirs are prone to slipping and cracking.
• Casing shearing during formation significantly impacts oilfield economic viability and development.
• Repeated damage at the same casing location suggests multiple cracks in weak structural surfaces.

Purpose of the Study:

• To propose and verify the geomechanical stick-slip theory for explaining reservoir structural failures.
• To develop a stress calculation method for weak horizontal structural surfaces considering inter-regional pore pressure differences.
• To analyze the influence of water inflow on formation stick-slip behavior.

Main Methods:

• Devised a stress calculation method for weak horizontal structural surfaces.
• Constructed a calculation model for shear stress release and slips on cracked surfaces.
• Analyzed formation stick-slip pressure considering water inflow and inter-regional pressure variance.
• Validated the model using data from Block X, Daqing oilfield.

Main Results:

• Under wet conditions, static and dynamic frictional stresses on cracked surfaces decrease significantly, increasing slip degree.
• The pressure difference required for subsequent slips decreases substantially after the initial crack and slip event.
• Continuous slips lead to gradual expansion of the slip range with increasing inter-regional pressure variance.

Conclusions:

• The geomechanical stick-slip theory provides a framework for understanding casing damage in oilfield development.
• Water significantly exacerbates the risk of slippage and casing damage.
• Understanding pressure dynamics is crucial for preventing and controlling casing damage in vulnerable reservoir zones.