Well productivity in the Ponta Grossa dike Swarm, Brazil: An integrated study with magnetic data inversion and clustering analysis of model solutions

Abstract

Dike swarms are mega-structures observed in different geological contexts which may affect groundwater flow systems. These structures are well recognizable from airborne magnetic, however it is difficult to obtain quantitative information about distribution and mean properties of dikes that generate the observed magnetic anomalies. This work presents a procedure to perform magnetic data inversion along profiles transecting the Ponta Grossa Dike Swarm (PGDS) and determine its mean properties with application of cluster analysis to obtained solutions. Next, the mean model solutions are correlated with a regional database of borehole productivity suggesting that more productive wells are found close to a group of shallow dikes of the PDGS in Southeastern Brazil. For the area mainly composed by sedimentary rocks, the wells situated over shallow dikes show higher values of specific capacity by a factor of 14.5 than those not close to a dike in the same domain. For the area mainly composed by granitic rocks, the productivity of wells over dikes is still higher, a factor of 4.3 higher than those with no dikes. A conceptual model is presented to explain the higher productivity of wells close to the dikes, as resulting from fracturing on host rock caused by dikes emplacement. Only a group of shallow dikes seems to be associated with more productive wells.