储能系数在确定气藏边界中的应用--以AY气田GS6井区龙王庙组气藏为例

Energy-storage coefficient to determine reservoir boundary:An example from Longwangmiao Formation, GS6 well block, AY gasfield, Sichuan Basin

确定含气面积是天然气储量计算的关键,目前大多采用有效储层厚度作为划分边界的依据。统计表明,在四川盆地碳酸盐岩气藏中,当有效储层较薄(<10 m)时,气井产能与单个的储层特征参数相关性较低[1]。通过对四川盆地AY气田龙王庙气藏特征的研究,采用储能系数作为储量计算的含气面积的边界划分依据。岩心样品实验和实钻井资料研究表明,储能系数和单井测试产量成正相关。选用模拟实际地层条件下压力和温度的产能模拟实验得到产工业气流的最低储能系数,通过储层预测得到储能系数平面分布图,从而确定气藏的岩性边界,圈定含气面积,计算的天然气探明储量已于2019年顺利提交国家储委审核通过。研究结果表明:①储能系数能兼顾反映储层厚度、物性等特征,能定量表征储层的储集能力和产能大小;②通过产能模拟试验获得的产工业气的最低储能系数值与测试证实的储能系数值相关性高,可用于确定含气边界;③采用储能系数代替此前的储层厚度来确定气藏的含气边界划分,其结果更为准确可靠。

Determining gas-bearing area is the key to reserve calculation. In the process of its determination, an effective reservoir thickness is mostly taken as boundary basis. Moreover, some statistics show that, for most carbonate gas reservoirs in Sichuan Basin, their well productivity is less correlative with single reservoir characteristic parameter when the effective reservoir thickness is less than 10 m. So, an energy-storage coefficient was taken as the boundary basis to calculate reserves after analyzing reservoir characteristics of Longwangmiao Formation, AY gasfield, Sichuan Basin. Core data and actual drilling data indicate that this coefficient is positively correlated with single-well test production. Then, the minimum coefficient was obtained by means of productivity simulation under both pressure and temperature of simulated actual formation. And its plane distribution map was plotted by means of reservoir prediction. And accordingly, the lithologic boundary of gas reservoirs was determined and the gas-bearing area was delineated. The calculated proven reserves were smoothly submitted to the State Reserve Committee in 2019. Results show that(1) this energy-storage coefficient can not only reflect reservoir characteristics simultaneously(such as thickness and physical properties) but also quantitatively characterize storage capacity and productivity;(2) the minimum coefficient obtained from productivity simulation is highly correlated with another verified in some tests, so it can be used to determine the gas-bearing boundary;and(3) when the coefficient is used to replace reservoir thickness to determine the gas-bearing boundary, the obtained result is more accurate and reliable.