Permeability for Columbia River Basalt Group, USA

Hydraulic conductivity estimatesfor CRBG aquifers were taken from the USGS National Water Information System (NWIS) database (Kahle et al. 2011) and converted to permeability estimates using temperature estimates from the nearest temperature profile log (Fig. 2). Temperature was estimated by using a best linear fit to the 100 m of borehole temperature log closest to the depth of the aquifer test. Viscosity and density were estimated as a function of temperature, and hydraulic conductivity was converted to permeability by multiplying by viscosity and dividing by the product of density and the gravitational acceleration constant (Fetter 1994, p. 96). Bulk permeability was computed using the layered system approximation (the arithmetic mean), assuming that the aquifer occupies 10% of the total thickness and that the permeability of the lava flow interiors is negligibly small. The detailed CRBG aquifer transmissivity estimates of Spane (2013) were also converted to estimated permeability (Fig. 4). First, estimated transmissivity was converted to bulk hydraulic conductivity by dividing by 30 m or the open length of the borehole, whichever was longer. Short open boreholes were assumed to test individual aquifers, so a typical lava flow thickness of 30 m was assumed to convert the aquifer test to a bulk permeability by using the layered system approximation (Fetter 1994, p. 123–124). Long open borehole tests (>30 m) potentially intersected multiple aquifers and a representative length of confining unit. Temperature measured in these boreholes (Schroder & Strait 1987; McGrail et al. 2009; Spane et al. 2012) was used to correct viscosity and density, and permeability was computed and assigned to the middle of the test interval. Four boreholes have multiple packer tests vertically along the borehole length.

哥伦比亚河玄武岩组（Columbia River Basalt Group, CRBG）含水层的水力传导系数（hydraulic conductivity）估算值取自美国地质调查局（United States Geological Survey, USGS）国家水信息系统（National Water Information System, NWIS）数据库（Kahle等，2011年），并结合最近的温度剖面测井（图2）得到的温度估算值转换为渗透系数（permeability）估算值。温度通过对距含水层试验深度最近的100m钻孔温度测井数据进行最优线性拟合得到。流体黏度与密度均以温度为函数进行估算，依据Fetter 1994年版第96页所述方法，通过将水力传导系数乘以黏度，再除以密度与重力加速度常数的乘积，将水力传导系数转换为渗透系数。整体渗透系数采用层状系统近似法（算术平均法）计算，假设含水层占总厚度的10%，且熔岩流内部的渗透系数可忽略不计。斯潘内（Spane）2013年提出的CRBG含水层详细导水系数（transmissivity）估算值同样被转换为渗透系数估算值（图4）。首先将估算得到的导水系数除以30m与钻孔裸露段长度二者中的较大值，得到整体水力传导系数。对于短裸露钻孔，假设其仅针对单个含水层进行试验，因此采用典型熔岩流厚度30m，并依据Fetter 1994年版第123–124页所述的层状系统近似法，将含水层试验结果转换为整体渗透系数。裸露长度超过30m的长钻孔试验可能会穿透多个含水层及代表性隔水单元，利用这些钻孔中测得的温度（Schroder & Strait，1987年；McGrail等，2009年；Spane等，2012年）对黏度与密度进行校正，计算得到的渗透系数被赋值至试验段的中点位置。共有4个钻孔沿钻孔纵向开展了多次封隔器试验（packer tests）。