WATER QUALITY CHARACTERIZATION OF AQUIFERS IN MEXICO: A PROPOSAL FOR MONITORING GROUNDWATER SYSTEMS IN AREAS OF SHALE-GAS PRODUCTION

Recent changes in the Energy Reform in Mexico have driven PEMEX’s objectives for the near future, including the increase rate of extraction of proved reserves from existing fields through optimization of hydraulic fracturing and unconventional drilling (multilateral, high angle and horizontal). The Burgos Basin (Tertiary-age) in Mexico covers most of the northern region of the Tamaulipas and Nuevo Leon states; it is the southern extension of the Maverick basin in Texas. The Eagle Ford shale Formation (Cretaceous-age) from south Texas continues to Coahuila state in northern Mexico, some shale gas/oil exploration wells drilled by PEMEX close to the USA border showed moderate results; however, prospective regions for oil and gas development are extensive, covering more than 1/3 of the Coahuila area. Additional targets are La Casita and Pimienta formations (Jurassic-age) in Coahuila. The Permian Basin in south-west Texas has also connection with some formations in northeast Chihuahua. The central and northeastern region of Mexico has a semi-arid condition and groundwater is the main source for domestic and public supply. South of the USA-Mexico border, there are at least 15 administrative aquifers along Rio Grande River, from the available hydrogeological information there is some hydrologic connection between the aquifer and the Rio Grande River, however there is uncertainty about the conditions of transboundary groundwater resources in the region. Actual conditions in these aquifers indicate some of them are under intensive development of groundwater. Experience from the USA can be used to estimate about 1000 to 36000 m3 of hydraulic fracturing water usage per well. This is not a high amount when compared with the total water supply for example for the northern border of Tamaulipas, estimated as 170000 m3 per day; however, it could be important on the local scale, creating additional pressure to already limited water resources and generate competition with the agriculture sector. In addition, water quality of aquifers for drinking water supply is under risk. Shallow groundwater contamination derived from drilling activities, connection between the shallow and deep geologic formations associated with faults and fractures, enhanced in the course of shale gas exploration and hydraulic fracturing and the injection of produced waters. The implementation of water-quality monitoring programs, the complete identification of nonrenewable groundwater or aquifers with limited natural recharge and the development of jointly research efforts, are mandatory for the sustainable water management along both sides of the USA-Mexico border region.