提升超深层超高压气藏动态储量评价可靠性的新方法——物质平衡实用化分析方法

超深层大气田一般都具有高压超高压、基质致密、裂缝发育等特点,其动态储量评价结果具有较强的不确定性。为了准确评价该类型气藏的动态储量,首先基于高压超高压气藏物质平衡方程,深入分析了岩石有效压缩系数与岩石累积有效压缩系数的相关关系,优选出适合于高压超高压气藏动态储量评价的物质平衡分析方法 ;然后,基于非线性回归法确定了动态储量评价的起算条件,针对未达到起算条件的情形建立了半对数典型曲线拟合法,并采用该方法计算了3个超高压气田(藏)的动态储量,进而验证其可靠性。研究结果表明:(1)高压超高压气藏物质平衡方程中的气藏累积有效压缩系数是影响该类气藏动态储量评价结果的关键参数,该参数是原始地层压力和当前平均地层压力的函数,而其数值难以通过岩心实验测得;(2)针对高压超高压气藏,推荐采用不需要压缩系数的非线性回归法进行动态储量评价;(3)采用非线性回归法计算动态储量的起算点(无量纲视地层压力与累计产气量关系曲线偏离直线的起点)无法通过理论计算得到,基于图解法的统计结果得到不同无量纲线性系数(ωD)情形下起算点对应的无量纲视地层压力衰竭程度介于0.06～0.38,基于实例气藏数据统计得到的起算点也在此范围内;(4)未达到起算条件时可采用半对数典型曲线拟合法估算动态储量,动态储量与视地质储量的比值(G/G_(app))是ωD的函数,ωD越大,(G/G_(app))越小;(5)处于试采阶段的高压超高压气藏,应尽可能延长试采时间,以提高动态储量评价的可靠性;对处于开发中后期的高压超高压气藏,则应以动态储量为基础制订气藏综合治理措施,进而不断改善气藏的开发效果。

A material balance based practical analysis method to improve the dynamic reserve evaluation reliability of ultra-deep gas reservoirs with ultra-high pressure

Ultra-deep major gas fields are typically characterized by high and ultra-high pressure, tight matrix and developed fractures, so the dynamic reserve estimation is of higher uncertainty. In order to accurately estimate the dynamic reserves of this type of gas reservoir, this paper analyzed the correlation between the effective rock compressibility and the cumulative effective rock compressibility based on the material balance equation of high and ultra-high pressure gas reservoirs, and accordingly selected the material balance based analysis method suitable for the dynamic reserves estimation of high and ultra-high pressure gas reservoirs. Then, the starting calculation conditions of dynamic reserve estimation were determined using the non-linear regression method. In addition, a semi-logarithmic type curve matching method was established for the cases where the starting conditions could not be met. Finally, this method was applied to calculate the dynamic reserves of three ultra-high pressure gas fields (reservoirs) to verify its reliability. And the following research results were obtained. First, the cumulative effective compressibility of gas reservoir in the material balance equation of high and ultra-high pressure gas reservoir is a key parameter influencing its dynamic reserves, and it is the function of original formation pressure and current average formation pressure, but its numerical value can be hardly obtained by core experiments. Second, it is recommended to adopt the nonlinear regression method without compressibility to estimate the reserves of high and ultra-high pressure gas reservoirs. Third, the calculation starting point of dynamic reserves by the nonlinear regression method (the starting point of dimensionless apparent formation pressure-cumulative gas production curve deviating from the straight line relationship) cannot be theoretically calculated. The calculation starting point for different dimensionless linear coefficients (ωD) obtained from the statistical results by the graphic method corresponds to the dimensionless apparent pressure depletion degree of 0.06-0.38, and that obtained based on the data statistics of the example gas reservoir falls within this interval. Fourth, when the starting conditions are not satisfied, the semi-logarithmic type curve matching method can be used for reserve estimation. The ratio of the dynamic reserves to the apparent geological reserves G/Gapp is a function of ωD. The higher the ωD, the lower the G/Gapp. Fifth, for the high and ultra-high pressure gas reservoirs in the production test stage, the test production time shall be extended as long as possible to improve the reliability of dynamic reserve estimation. And for those in the middle and late stages of development, it is necessary to prepare the comprehensive treatment measures on the basis of dynamic reserves so as to improve the development effects of gas reservoirs continuously.