Application and research into dilatation and injection enhancement technology for unconsolidated sandstone injectors in an offshore oilfield

There are widespread problems with high injection pressure and low water injection in the process of water injection development in offshore oilfields. The conventional acidification measures are short-lived and have high operating costs, which seriously affects oilfield development. High-pressure dilation technology can improve the injection rate and extend the effective period of injection. The representative unconsolidated sand core samples were taken from the offshore oilfield for rock mechanics tests, dilation laboratory simulation experiments and numerical simulations, to study the dilation mechanism and main controlling factors of unconsolidated sandstone in offshore oilfields, and the dilation technology has been applied in offshore oilfields. It is shown that the dilation angles of unconsolidated sand in offshore oilfields are much larger than those of the Athabasca oil sand in Canada, which has the basic conditions for applying dilation technology. It is conducive to the development of complex shear and tensile areas with a slow injection rate, but a high injection rate tends to form a single crack. It is beneficial to generate complex shear and tensile areas with minimum principal stress. The dilation area expands in a long strip, which is perpendicular to the direction of the minimum principal stress. Shear cracks and tensile cracks coexist in the dilation area, and the large shear area contains small narrow-band tensile areas. Under the same condition of water injection, the shear dilation and tensile dilation areas will increase with shallower reservoir buried depth and greater permeability. The dilation technology can provide guidance for the development of water injection in offshore oilfields, and has good prospects of application.