Research On Sealing Capability Of Cementing Packing System In Sandstone Formation

Cementing is an important part of drilling engineering,and its main purpose is to achieve tight interlayer separation and protection of casing,ensuring that subsequent production operations are carried out safely and effectively.The quality of cementing depends on the sealing effect of cementing cement ring and the first and second interfaces of cementing.At present,more than half of the oil and gas reservoirs developed are sandstone oil and gas reservoirs.Although the reservoirs have good caprocks,the cementing and packing integrity of the sandstone oil and gas reservoirs themselves plays a good role in the upward channeling of oil and gas in the entire sealing system.For this reason,this paper has carried out a study on the sealing ability of cementing isolation lengths in sandstone formations with different permeability,in order to provide a basis for the implementation of cementing isolation in sandstone oil and gas reservoirs.Based on previous studies,this paper uses the capillary model and the gas percolation theory to study the fluid flow in the cement stone from the micro and macro perspectives,and explores the influencing factors and mechanism of the sealing performance of the cement stone.The sealing pressure of cement stone was measured through experiments,and some influencing factors were verified.Using a self-designed interface sealing performance test device,the sealing pressure of the first and second interfaces of cementing with different lengths was simulated and tested.The tension-displacement curve of the interface is experimentally measured by the improved tensile method.Based on the cohesive force unit model in the cohesive force model,an interface sealing model is established,and the process of fluid breaking through the interface is simulated.The tension-displacement curve,fluid breakthrough interface area morphology,and interface sealing pressure obtained from the experiment and simulation results are in good agreement,which proves the feasibility of the cohesion unit to simulate the interface cracking and the cohesion unit measured by the improved tensile test the accuracy of the parameters.On this basis,a quantitative evaluation method for the sealing performance of the first and second interfaces of sandstone formation cementing was established.Studies have shown that water in the pores of cement stone is a prerequisite for its own sealing performance.With the increase of capillary pressure,pore fluid pressure,and the additional pressure difference generated by the Jiamin effect,the sealing ability of cement stone to fluids is enhanced.The sealing performance of the first and second interfaces of cementing will increase with the increase of the tensile strength of the interface,the squeezing stress of the interface,the fracture energy of the interface,the elastic modulus of cement stone and sandstone,and it is affected by the Poisson ratio of sandstone and cement stone.Smaller,it will decrease with the increase of sandstone or cement stone permeability.When the permeability is lower than 0.001 m D or higher than 10 m D,the sealing pressure of the interface to the fluid will no longer change significantly.After the interface length exceeds a certain value,the sealing pressure of the interface will not increase as the length increases.