An one-dimensional model for contaminant advection and dispersion through a GCL/AL liner system was developed to analyze the equivalence between a GCL(geosynthetic clay liner) and a CCL(compacted clay liner).The continuity of contaminant concentration and flux at the interface between the GCL and the underlying attenuation liner(AL) are obeyed in the model,and background concentrations in the soil liner are also considered.Based on the assumption that contaminant transport through a GCL was a steady state process,an analytical solution was obtained.Increasing the leachate head from 0.3 m to 10 m results in a reduction of the breakthrough time of benzene by a factor of 2.7.The breakthrough time of benzene increases by a factor of 7.0 when the hydraulic conductivity of GCL decreases by one order of magnitude.The breakthrough curves are more sensitive to the hydraulic conductivities of the GCL and AL(attenuation layer) than to the thickness of the AL.The standard 75 cm CCL can be replaced by a combination of a GCL and a 1.0-4.0 m thickness of AL.The proposed method can be used for preliminary design of GCL composite liners,assessing the equivalence between GCL and CCL,preliminary design of a remediation method for contaminated soils,and evaluating experimental results.
The Ordovician carbonate reservoirs in the Tahe Oilfield are highly heterogeneous, which have undergone multiple superimposed transformations by tectonic activities and karst processes, leading to an extremely complex fluid distribution. The geochemical characteristics of geofluids also display great disparities. Results show that the vertical distribution of oil and gas are continuous, however the oil-water interfaces in different blocks of the Tahe Ordovician Oilfield are numerous. Meteoric water infiltration is regarded as the main reason for the high oil-water interface and high water content to the north of Tahe Oilfield, especially in well blocks S78–S73. The isotopic values of deuterium-oxygen in the groundwater and carbon-oxygen from calcite veins confirm that formation water in Ordovician reservoirs of the Tahe Oilfield was a mix of meteoric water and connate water, and the proportion of meteoric water gradually increases from south to north, while connate water decreases. The Tahe Ordovician reservoirs are characterised by multiple hydrocarbon charges, and the general migrating direction is from southeast to northwest and from east to west. High production could be obtained in the northern area of the Tahe Oilfield since the oil layers are thick and oil is highly saturated. The residual water within the reservoirs is low, and heavy oil is dominant in this area. Only a small amount of pore water has been replaced by oil in the southern Tahe Oilfield, leading to low oil saturation and a high content of residual water. Crude oil is herein mainly of medium-light type. During the process of exploration in this region, acid fracturing reformation is usually required for wells to increase their output; however the yield is still low.
