凝析气藏循环注气开发中后期重力分异特征

GRAVITY SEGREGATION OF THE CYCLIC GAS INJECTION IN THE CONDENSATE GAS RESERVOIRS IN THE MIDDLE AND LATE DEVELOPMENT STAGES

Y凝析气藏经多年注气开发后,气藏在不同产层剖面上呈现出不同的气油比变化和产出烃组分分异现象。利用井下取样方式取得最新的地层流体,通过相态实验,发现随着深度的加深,气油比逐渐增加,露点逐渐增大,凝析气相对分子质量逐渐增大等分异现象。通过干气-凝析气非平衡扩散实验,发现注入的干气并未马上与凝析气混为一相,试验压力为露点压力时,干气注入凝析气后呈现出上层干气、中层凝析气、下层凝油三种地层流体从上到下的分布现象,而实验压力大于露点压力时,呈现出上层干气、下层凝析气两种气体共存的现象。对长期注气开发、气窜等原因导致的重力分异现象有了清晰认识,对注气层位优选等开发方案调整具有重要意义。

After years of the gas injection development in Condensate Gas Reservoir Y, the phenomena of the gas- oil ratio changes and composition segregation occur in different cross sections of the producing layer. By the method of underground sampling, the latest formation fluids are obtained, the phase behavior experiment shows that the fol- lowing segregational phenomena： the ratio increases with the depth, the dew point increases as well, the relative mass factors of the condensate gas are gradually enhanced and so on. Through the dry gas and condensate gas diffu- sing experiment, the injected dry gas is discovered not to mix into one phase with the condensate gas immediately, when the test pressure is lower than dew point pressure, the following distribution phenomenon occurs from the top to bottom for the formation fluids： the dry gas, condensate gas and condensate oil, but when the experimental pres- sure is higher than the dew point pressure, the coexisted phenomenon of the two kinds of the gas appears ： the dry gas is in upper part, the condensate gas is in deeper part. The gravity segregation phenomena caused by long-term gas injection development, gas channeling and the other reasons are made clear, these achievements possess impor- tant significances for the developing program adjustment such as the gas injected layer optimization and so forth.