Abstract
Abstract. The possible effect of water injection to mitigate land subsidence was studied through numerical simulations based on the theory of poroelasticity. The Kujukuri Plain, Japan, was chosen as a study area. The effect of past injection was evaluated by comparing a model with injection and the one without injection. The calculated results suggested that the past injection played a significant role to reduce land subsidence. For achieving more effective mitigation practices in the future, we proposed to install injection wells in shallower formations. The effect of proposed injection method to mitigate land subsidence from 2014 to 2030 was also investigated. The calculated results show that the proposed method can work similarly by lesser water injection than the past method. The results also indicate that the upper limit of injection rate should be carefully determined to control the pore pressure build-up in the formation to be small enough to avoid formation failure.
Highlights
The production of natural gas and iodine dissolved in groundwater has continued for more than 50 years at the Kujukuri Plain, Japan, and it has caused land subsidence problem in the area
It is important to examine the design of water injection wells, both in spatial and injection scheme points of views, to make the mitigation of land subsidence more effective
The contribution of past water injection to the reduction of land subsidence was found to be about 30 cm (20 %) at the point of maximum subsidence. This suggests that the past injection played a significant role to reduce land subsidence
Summary
The production of natural gas and iodine dissolved in groundwater has continued for more than 50 years at the Kujukuri Plain, Japan, and it has caused land subsidence problem in the area. The design of spatial distribution of injection wells was not optimised because the injection wells were mainly converted from abandoned production wells This approach has caused a risk of reservoir deterioration because the formations into which water has been injected are the same as those from which natural gas and iodine are produced. It is important to examine the design of water injection wells, both in spatial and injection scheme points of views, to make the mitigation of land subsidence more effective. To quantitatively discuss the effect of water injection into the shallower formations on land subsidence mitigation, a numerical modelling which can calculate the coupled process of both groundwater flow and deformation in subsurface formations is one of the approaches which we can use. The effect of past and possible furture water injection is investigated through poroelastic simulations at K-district (Fig. 2, Table 1)
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