超临界CO2酸压过程中碳酸盐岩多尺度力学参数衰减机制OA

To overcome the issues of conventional acid fracturing in deep,high-temperature carbonate reservoirs with low pres-sure coefficients-namely overly rapid reactions,short effective penetration distances,low fracture conductivity,and difficult post-fracture flowback-this study performed soaking experiments on tight carbonates of the Majiagou Formation at 110 ℃ and 30 MPa using supercritical CO2(SC-CO2)and SC-CO2 plus formation water.Integrating X-ray diffraction(XRD),scanning electron microscopy(SEM),nanoindentation,and uniaxial compressive tests,we constructed a coupled mineral-microstructure-micro/macro-mechanics evolution framework.The results indicate that pure SC-CO2 is characterized by de-dolomitization ac-companied by secondary calcite precipitation;with the addition of formation water,the regime shifts to carbonic-acid-dominated dissolution,manifested as preferential dissolution of calcite with relative enrichment(and possible recrystallization)of dolomite.The soaking process exhibits staged evolution:early de-dolomitization with secondary precipitation;a middle stage of intensi-fied calcite dissolution with dolomite enrichment/recrystallization;and a late stage marked by increased porosity and connectiv-ity and the emergence of channelization(wormholing).SEM shows surface evolution from pitting to grooves and through-going pores,with calcite more reactive than dolomite.Nanoindentation reveals power-law decay in hardness and elastic modu-lus-pronounced early softening followed by a short-term rebound and subsequent re-softening.At the macroscale,mechanical properties degrade concurrently:compressive strength and elastic modulus decrease markedly,Poisson's ratio increases,the load-bearing framework weakens,and ductility is enhanced.