Study of stress-strain properties of base cement sheath for oil and gas wells cementing

UDK: 622.245.422

DOI: 10.24887/0028-2448-2025-7-26-29

Key words: cement sheath, well cementing, tensile strength, mechanical properties, stress-strain properties, laboratory studies

Authors: I.I. Girfanov (TatNIPIneft, RF, Almetyevsk); I.T. Usmanov (TatNIPIneft, RF, Almetyevsk); R.S. Gufronov (TatNIPIneft, RF, Almetyevsk); D.R. Sabirzyanov (TatNIPIneft, RF, Almetyevsk); I.R. Mukhliev (TATNEFT PJSC, RF, Almetyevsk)

The requirements for the properties of cement grades produced and used in the construction of oil wells are defined in state standards. The main parameter is the bending strength at various application temperatures. However, whether cement strength is sufficient to withstand the range of loads experienced during well operation at particular productive formations remains unclear. Samples of one of the cement grades used in production operations were obtained under pressure and temperature conditions of formations under development, strength properties were investigated for a range of loads in the near-wellbore intervals. A pseudo-triaxial loading setup was used for the experiments. Cement sheath failure envelopes were developed with samples breakdown by conditions of formation. Internal friction angles according to research findings were obtained in a narrow range of 29-31 °. Ultimate cement strength ranges from 53,9 to 102,6 MPa, an increase in cement strength with increasing confining pressure is observed. The obtained strength values are sufficient for the cement sheath to maintain its integrity in situ during production operations. Numerical modeling of the stress-strain state in the near-wellbore area also requires elastic cement properties. Some tasks require understanding of elastic properties depending on pressure changes. Young's modulus and Poisson's ratio are determined for stress conditions typical for producing oil fields of the Republic of Tatarstan. There is a slight difference between ultimate strength and elastic property ranges for two conditions of cement sample formation. Hence, the general failure envelope with single states limit is applicable.

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