基于峰值预测的天然气产量风险量化评价——以川中古隆起震旦系气藏为例

Quantitative risk evaluation on natural gas production based on peak prediction:An example from Sinian gas reservoirs,central Sichuan paleo-uplift

大气田建设之初,峰值产量预测及风险量化研究是规划决策的重要内容。四川盆地震旦系地层古老,气藏埋藏深,多年的持续探索,展现出巨大的勘探开发潜力。以川中古隆起震旦系气藏为例,通过将最终可采储量(URR)作为边界条件,采用峰值模型预测气藏产量增长趋势。基于产量预测结果,采用蒙特卡洛模拟法计算产量实现概率,将概率曲线与风险等级矩阵叠置,评判目标气藏风险等级,实现了气藏从规模预测到风险量化的全过程研究,构建了完整的天然气战略规划风险决策量化体系。研究结果表明:①震旦系气藏将于2036年达到130×108~251×10^(8) m^(3)/a的产量峰值,相对稳产期8年。②以峰值模型预测结果为基础,将最终可采储量URR为自变量的产量增长曲线进行蒙特卡洛模拟,求取了各年份产量实现概率P,模拟结果表明震旦系气藏2030年累计概率P50对应的产量为131×10^(8) m^(3)。③以实现概率P和离散程度C为评价指标建立风险等级评价矩阵,产量上升阶段和产量缓慢递减阶段的离散程度C∈(5%,10%),风险等级范围Ⅱ~Ⅳ级;产量稳定阶段与产量快速递减阶段的离散程度C∈(10%,25%),风险等级范围Ⅲ~Ⅳ级,产量目标实现风险综合评价。

To predict peak gas production and to quantify risks are crucial in planning and making decisions at the begin-ning of constructing a giant gasfield.There exist deep gas reservoirs in the age-old Sinian,Sichuan Basin.Their continu-ous exploitation for many years displays great exploration and development prospects.So,taken the Sinian gas reservoirs in central Sichuan paleo-uplift as examples,their production incremental tendency was predicted by using the peak model with ultimate recoverable reserves(URR)as boundary conditions.Based on prediction results,the production realization probability was calculated by adopting the Monte Carlo simulation.Then,the probability curve and the risk rating matrix were superimposed to assess the risk rating of the target.As a result,the whole process research was realized for gas reser-voirs from scale prediction to risk quantification,and a complete quantification system on risk decision was constructed for the strategic planning of natural gas.Results show that(1)for the Sinian gas reservoirs,the production will peak at(130–251)×10^(8) m^(3)/a in 2036 with relatively stable 8-year periods;(2)based on results predicted from the peak model,the Monte Carlo simulation is carried out on production increase curves with URR as an independent variable to compute the produc-tion realization probability P for every year.Simulation illustrates that the output in the Sinian reservoirs will be 131×10^(8) m^(3)in 2030 corresponding to the cumulative probability P50;(3)the risk rating evaluation matrix is established by taking the realization probability P and dispersion degree C as evaluation indexes,i.e.,dispersion degree C∈(5%,10%)and risk rating rangeⅡ–Ⅳin production-increasing and slow decline stages,whereas dispersion degree C∈(10%,25%)and risk rating rangeⅢ–Ⅳin stable production and rapid decline stages,respectively.Actually,production aims can be achieved through the comprehensive risk evaluation.