Phase Characteristics of Fluids in Offshore Buried Hill Condensate Gas Reservoirs and Their Influence on Formation Permeability.

The BZ gas field is the first large gas field in the Bohai Sea of China, with reserves of 100 billion cubic meters. Its formal operation can greatly promote local green and low-carbon development. However, the condensate gas reservoir has characteristics such as a large burial depth, a steep temperature and pressure gradient, high condensate content, developed microfractures, and a small pressure difference between the surface and dew point. As a result, the retrograde condensate phenomenon will occur in the early stage of gas field development, which will lead to more condensate remaining in the reservoir pores and cannot be recovered if depletion production is adopted. In order to improve the recovery of this reservoir, the influence of dry gas injection in different proportions on the phase behavior of formation fluid is studied by compounding original formation fluid through laboratory experiments. Then, under the conditions of high temperature and high pressure, a retrograde condensate permeability damage experiment was carried out on the actual buried hill metamorphic rock core from the BZ condensate gas reservoirs, with the gas effective permeability measured at different pressures. The results show that gas injection can extract retrograde condensate oil, reduce its saturation, and improve the recovery of condensate gas reservoir. Early injection and higher pressure injection are more conducive to enhancing recovery. The retrograde condensation damage experiment shows that permeability damage is more severe in lower permeability cores, and the presence of fractures aggravate this damage. The study can provide basic parameters for physical and numerical simulation experiments of gas injection in long cores and can also have positive enlightenment significance for global deepwater oil and gas development.