To address the unclear mechanical response mechanisms of the cement sheath in deep oil and gas well cementing under complex temperature-pressure conditions，this study systematically investigated the coupled effects of curing temperature，curing pressure，testing temperature，and confining pressure on the mechanical properties of Class G oil-well cement. Specimens were prepared at different curing temperatures ranging from 25°C to 140°C and curing pressures of the atmospheric pressure and 21.7 MPa. Triaxial compression tests were then conducted at different testing temperatures from 25°C to 140°C and confining pressures from 0 to 20 MPa to analyze the evolution of stress-strain curves，peak stresses，and elastic moduli. The results show that increasing curing temperature reduces the peak stress and elastic modulus of the set cement，while high-pressure curing significantly inhibits pore development and improves structural compactness. Increasing testing temperature helps enhance the mechanical performance of cement at the testing temperature close to its curing temperature. Increasing confining pressure improves the plasticity and residual strength of cement，and the cement exhibits staged evolutionary characteristics under different coupled conditions. The findings of this study provide a theoretical basis and experimental support for the design of cement slurry systems and the integrity evaluation of cement sheaths in deep formations.

Poor pore-permeability，high shale oil viscosity，strong reservoir-wellbore flow risk，low primary recovery and single unsuitable slickwater fracturing fluids are the problems facing the development of Jimusar shale oil. SDY-1+XC-4，a multifunctional slickwater fracturing fluid system，was developed based on SDY-1，a multifunctional fracturing-enhanced oil recovery (EOR) material for viscosity reduction，oil washing，and imbibition. The performances of temperature and shear resistant，viscosity reduction，oil washing and imbibition were evaluated through laboratory experiments. Its applicability under reservoir temperature and salinity was analyzed. And the slickwater system has been applied in Jimsar. Results showed that SDY-1 has high compatibility with XC-4. SDY-1+XC-4 exhibits good temperature and shear resistance at reservoir temperature. At 30 ℃，the viscosity reduction rate of SDY-1+XC-4 is 93.68%，the oil washing efficiency is 66.7%，and the imbibition recovery rate is 33.24%. SDY-1+XC-4 works well under the reservoir temperature and salinity. The field testing results showed that the test well presents cumulative oil increase of 2 031.6 t，compared with the reference well. The development and application of the multifunctional fracturing-EOR materials can provide a solid foundation and technical support for the efficient development of Jimsar shale oil.

With the extensive applications of new technologies such as zipper fracturing in shale oil and gas development，the casing is subjected to both the multi-stage cyclic internal pressure and the external non-uniform compressive load caused by zipper fracturing operations. Given this，this paper analyzes the variation law of casing collpase strength under multi-stage cyclic load and zipper fracturing of platform wells via the multi-stage cyclic load experiments and numerical simulations. The calculation method of the casing comprehensive collapse strength coefficient under multi-stage fracturing is developed and applied to a casing-deformed well in  Xinjiang Oilfield. The results show that the casing collapse strength decreases linearly with the number of load cycles under cyclic loading. Zipper fracturing results in the non-uniform stress distribution around the well，and the casing collapse strength nearly linearly decreases with the increasing stress non-uniformity. Under the combined effects of internal and external loads，the casing collapse strength drops by more than 15%，which increases risks of casing deformation. The calculation method of casing callopase strength in platform wells proposed in this paper provides calculation guidance for the prevention of casing deformation in fracturing practice.