基于气水相渗曲线的低渗气藏有效厚度下限方法研究——以东海西湖凹陷HY区为例

Study on the lower limit of effective thickness for low permeability gas reservoirs based on gas-water relative permeability curves:Taking HY area of Xihu Sag,East China Sea as an example

东海盆地西湖凹陷低渗砂岩气藏规模巨大,目前已逐渐成为开发主力。由于低渗气藏具有储层致密、物性差、孔渗关系复杂、电性响应不明显的特点,利用常规统计方法研究有效厚度下限具有一定的不确定性,有必要针对低渗气藏的特点进行下限研究。以测试层、生产层产能资料为基础,依据气水两相渗流理论,提出了利用相渗曲线评价下限的方法,通过建立产气量与气层厚度、渗透率、含水饱和度、生产水气比的函数关系,综合储量起算标准、生产水气比临界值确定各个参数的下限值,建立一个多参数综合表征下限的有效厚度下限标准。结果表明,西湖凹陷HY区气层厚度主要分布在20~30 m,渗透率3×10^(-3)μm^(2)及以上气藏含气饱和度下限为50%;渗透率(1~3)×10^(-3)μm^(2)气藏含气饱和度下限为60%,在含气饱和度低于60%时需要采用水平井开发;对于渗透率110^(-3)μm^(2)以下、含气饱和度低于50%的气藏,需要进行储层改造才具有开发价值。实际生产井验证表明,该方法确定的有效厚度下限合理,更能综合表征产能及其影响因素,对储量评价中有效厚度下限的确定及探井测试选层均具有较强的指导意义。

The low permeability sandstone gas reservoirs in the Xihu Sag of the East China Sea Basin are huge in scale,and have gradually become the main force of development.Since low permeability gas reservoirs are characterized by dense reservoirs,poor physical properties,complex pore-permeability relationships,and inconspicuous electrical response,there is a certain uncertainty in studying the lower limit of effective thickness using conventional statistical methods,and it is necessary to conduct lower limit studies for the characteristics of low permeability gas reservoirs.Based on the production capacity data of the DST and production layers,and according to the gas-water two-phase seepage theory,it is proposed a method of evaluating the lower limit using phase seepage curves.By establishing the function relationship between gas production and gas formation thickness,permeability,water saturation,and production water-gas ratio,the lower limit value of each parameter is determined by integrating the standard of reserve calculation and the critical value of production water-gas ratio,and an effective thickness lower limit standard is established with a multi-parameter comprehensive characterization of the lower limit.The results show that the gas thickness in the HY area of the Xihu Sag is mainly distributed in the range of 20-30 m,the lower limit of gas saturation in gas reservoirs with permeability 3×10^(-3)μm^(2)and above is 50%,the lower limit of gas saturation in gas reservoirs with permeability(1-3)×10^(-3)μm^(2)is 60%,and horizontal well development is required when the saturation is lower than 60%.For gas reservoirs with permeability below 1×10^(-3)μm^(2)and gas saturation below 50%,reservoir modification is required for development value.The validation of the actual production wells shows that the lower limit of effective thickness determined by this method is reasonable and more comprehensive in characterizing the production capacity and its influencing factors,which is a strong guiding significance for the determination of the lower limit of effective thickness in the reserve evaluation and the selection of exploratory well testing.