Hydraulic Conceptual Model for a Pumping Project Field Management Plan in Berlin Geothermal Field, El Salvador

Abstract

A pump trial project has been completed, testing injection of produced brine at elevated pressure in a tight injection well TR-8A in Berlin Geothermal Field, El Salvador, with the purpose of improving the capacity of a defined injection zone of the field while ensuring uninterrupted power generation.

On average, a total of approximately 350 lt/s of produced brine are injected via two pipeline networks which include separators at various elevations under gravity feed owing to an approximately 150 m lower elevation than the production zone. The two pipeline networks, the high pressure system (HPS), and the low pressure system (LPS), run 9 bar apart.
To ensure uninterrupted injection capability that in turn ensures uninterrupted power generation, the two pipeline systems were connected via an "interconnector". (Figure 2)

To verify the base data calculated for a proposed field management plan (ChavarrÌa, 2003), it was used commercially available software (Plant-Flow) for the operation of the two interconnected pipeline systems during the trial injection at elevated pressure with Hazen William's equations for steady state flow analysis.

The plan considered to shut-in 4 of the 12 injection wells connected to the 2 pipeline networks to allow for full flexibility in the water supply for the high pressure injection.

The calculation suggested that at the interconnection of the two pipeline networks, the low pressure one would not be flooded provided the differential pressures ranged between 0 to 17 bar according with the flow pumped into TR8A reinjection well, while ensuring that the suction pressure would not reach its critical value.

With this plan, the operation program was developed and as a result, the suction pressure of the centrifugal pumps was by and large maintained in the range of values between 15 and 23 barg while providing the full range of required injection rates into TR-8A from 25 to 130 lt/s.

No discharges at lower elevation producer platforms were reported neither were there any uncontrolled discharges during normal pumping operation that lasted at peak rates uninterrupted for up to 2 weeks.

Injection at elevated pressures routinely of up to 80 - 110 bar proved to be a viable alternative to drilling of dedicated injection wells operating under gravity feed.