致密砂岩储层物性下限的确定——以鄂尔多斯盆地陇东地区山1段为例

Determining the lower limit of physical property in tight sandstone reservoirs: an example from Shanxi 1 Member, Longdong area, Ordos Basin

鄂尔多斯盆地西南部陇东地区上古生界下二叠统山西组1段属于典型的“低孔、低渗”致密砂岩储层,目前该区域处于勘探评价阶段,储层物性下限尚无统一标准,试气过程中多有干层出现,给评价工作的进展及钻采工艺技术的应用带来困难。因此,通过综合分析岩心资料、测井资料、测试成果,采用孔渗交会法、经验统计法、物性试气法、测井参数法多种方法计算得到物性下限。根据压汞资料,利用最小流动孔喉半径法建立孔喉中值半径与物性参数的拟合关系式,计算出物性下限。最后以5种方法计算结果的算术平均值作为陇东地区山1段储层物性下限,研究结果表明:①综合计算陇东地区致密砂岩储层孔隙度下限为4.6%,渗透率下限0.06mD;②利用多种方法计算相互验证确定储层物性下限,降低了单一方法对物性下限确定的偏差,取值更为合理;③物性下限的科学确定对于推进评价工作进展、计算地质储量、制定开发技术对策及确定气井的生产方式具有重要的指导作用。

The Upper Paleozoic Lower Permian Shanxi 1 Member (P1s1),Longdong area,southwestern Ordos Basin,is typical tight sandstone reservoirs with low porosity and permeability.At present,this area is still in an exploration evaluation stage,no unified standard is available for the lower limit of reservoirs’ physical property.Moreover,both evaluation progress and an application of drilling technology were severely restricted due to several dry layers frequently discovered during formation testing.So,based on some core, well-logging,and testing data analysis,the lower limit was obtained respectively by means of four methods including porosity-permeability crossplot,empirical statistics,physical-property testing,and logging parameters.Then,based on mercury-injection data,a fitting relation between median radius of pore throat and physical-property parameters was established by means of another method of the minimum flow pore throat radius to calculate this lower limit.Finally,the arithmetic mean of calculation results obtained by these five methods was taken as the lower limit of P1s1 reservoirs’ physical property.Results show that (1) the lower limit of porosity and permeability are 4.6% and 0.06 mD,respectively;(2) adopting these methods to determine and verify the lower limit can reduce the deviation of single method and obtain a reasonable limit;and (3) confirming the lower limit plays an important guidance in promoting evaluation progress,calculating geological reserves,making development technological countermeasures,and making production strategy.