MG9D Acid Well Utilization: Revisiting the Past and Harnessing its Future

Abstract

After being drilled in 1993, the prospect of using well MG9D for production became uncertain due to the low-pH and highly corrosive nature of its discharged fluids. Through the years, the experiences of other geothermal fields (like in Costa Rica) on acid well utilization and the research and pilot testing conducted on MG9D reinforced the current strategy of adapting a neutralization technology for the MG9D acid well utilization. The first downhole injection neutralization technology to be installed by EDC, the project is set to prove the effectiveness of the industrial application and hence serve as a prototype for future acid wells utilization requiring neutralization technology.

This paper presents a re-assessment of the previous chemistry simulations performed on acid well MG9D and attempts to identify potential problems that may arise with its utilization. Updated chemistry obtained from recent discharges were used to simulate mixing of MG9D in-situ fluid and NaOH solution based on newly acquired flash point and caustic soda injection depth data. The results were evaluated for consistency with previously specified dosing requirements. Chemistries of the resulting mixtures were also re-examined for saturation indices trends of the minerals anhydrite, calcite, amorphous silica and minnesotaite. Also, stratigraphy and structural permeability showed close proximity of MG9D to injection well MG21D at < 500m separation making the prospect of brine returns affecting MG9D utilization more pronounced. For this reason, mixing of MG9D in-situ fluids with MG21D injected brine chemistry was also modeled to investigate possible alterations in MG9D’s fluid chemistry that may affect the operation of the acid well utilization system. The initial commissioning performance of the industrial dosing system is also presented.