Hydraulic Fracturing In Sedimentary Basins: Numerical Simulation Of Potential Contamination Of Shallow Aquifers

Hydrofracturing is one of the most commonly used technology of shale gas.Hydrofracturing of deep shale beds to develop natural gas has caused concern regarding the potential for various forms of water pollution,however,domestic shale gas research is still in the initial stage,so most of the hydrofracturing of groundwater pollution from qualitative research,still less for quantitative research on the problem.Therefore,the study has significance for the future protection of groundwater in shale gas.This paper summarized the background of produced shale gas research;generalized previous studies about shale gas or analogous project in groundwater contaminants migration,and pointed out problems existed in previous studies.Illustrated the character of hydrofracturing and study area’s geological conditions by taking a shale gas block as an example.According to project’s character and study area’s geological condition,generalized reinjection area and its adjacency to a two-dimensional,homogenous,equal thickness,horizontal occurrence conceptual model.Compared numerical simulation software of groundwater,finally chose TOUGH2’s interfaced software PetraSim to build numerical model.In order to study the influence of hydrofracturing on groundwater,model A,model B and model C had been built to simulate hydrofracturing influence on salinity distribution according to three conditions which consider the influence on whether have fault or hydrofracturing zone.The results showed that:(1)Hydrofracturing would increase the salinity of the overburden in the area of shale bed near hydrofracturing well;(2)After the hydrofracturing,the influence scope of the fracturing fluid and underground deep brine is gradually expanding.The vertical diffusion of salinity is 0.18m/a;(3)If the hydrofracturing makes the fracture in the layer to run through,or fracturing near the fault,the time of contaminant transport to the shallow aquifer will be reduced to a few thousand years to ten thousand years;(4)Comparing the four kinds of conditions,the change of salinity is in the same change rule.In the same fault cases,the presence of horizontal wells have little impact on the contamination plume;(5)Model parameter sensitivity analysis results show that only porosity and permeability above shale,fault permeability above shale,fault anisotropy above shale and hydrofracturing zone distance to fault have influence on the simulation results.From results,we can see that with the increase of the porosity and permeability above shale,the front of the contamination plume decreases;with the fault permeability above shale or the fault anisotropy increase,the front of the contamination plume increases;with the increase of hydrofracturing zone distance to fault,the front of the contamination plume decreases.