关键词: 碳酸盐岩, CT扫描, 裂缝开度, 应力敏感性, 数值模拟

Abstract: To investigate the stress sensitivity of carbonate reservoir as well as its effect on oil and water productivities, seven rock
samples from the Upper Ordovician Lianglitage Formation of the southwestern Tarim Basin were selected for sensitive experiment.
Based on the experimental results and mathematical derivation, the relationship between stress-strain and fracture aperture of rock was
established. Spatial distribution of fracture aperture under various confining pressure and pore pressure was simulated through finite
element method. Results show that effective stress and fracture aperture change rate have a good inverse nonlinear proportional
relationship. Along with the increase of confining pressure, the fracture aperture decreases continuously, with a fast decreasing rate at
the initial stage (0-0.8 MPa). This indicates that the stress sensitivity of rocks is strong. To a high pressure (2.6 MPa or 5.4 MPa), the
aperture changes only a little, implying that the stress sensitivity is weakened under high stress and the plastic deformation is obvious.
With the decrease of confining pressure, the fracture aperture tends to be opened till to a zero pressure, but the aperture cannot be
restored to the initial state. This is indicative of certain plastic deformation. In the next few years, with continuous and rapid exploitation
in the Hetianhe Gas Field, the effective stress will increase, the fractures will tend to be closed and the productivity will decline.
However, along with discontinuous mining or manual well shutdown, the effective stress above the gas-water interface will still decrease
and the fractures tend to be closed. In contrast, the effective stress below the interface will increase, fractures tend to be opened and
bottom water rises to destroy the gas reservoir production. As such, we suggest that a fine study on the fracture distribution and the main
controls for fracture stress sensitivity must be carried out when shaping development plan for fractured carbonate gas reservoir.
Meanwhile, reasonable development model and producing rate should be developed and taken.

Key words: carbonate reservoir, CT scanning, fracture aperture, stress sensitivity, numerical simulation