Coupled Production Facility and Geothermal Well Performance Modelling: Case Studies and Insights

Abstract

Numerical modelling is an essential tool for the assessment of geothermal production facilities, for the evaluation of optimization opportunities, as well as for forecasting the future performance of a plant when change is introduced. In all these functions, numerical models support decision-making – be it for day-to-day response, or for strategy development. For two-phase, intermediate enthalpy production systems like in the Tiwi and Mak-Ban geothermal fields in the Philippines, transport phenomena have significant impacts on the overall system production. Transport can account for 65% (as high as 80% in cases) of the overall pressure difference between production wells and the plants, with the remainder due to processes such as separation and scrubbing. This presents an opportunity for the optimization of transport facilities for better field performance. Facilities Engineers in the Philippine Geothermal Production Company, Inc. (PGPC), which operate the Tiwi and Mak-Ban geothermal fields, have long utilized fluid transport facility numerical models in order to understand the process and to make strategic decisions. The earliest documented use of numerical modelling software in PGPC was in 1989 using PIPEFLOW, described as “an off shoot from the Tiwi pipeline network programs” (Wendt, 1989). Current softwares have certainly come a long way from PIPEFLOW, which was only capable of single pipeline calculations. Commercially available transport modelling softwares primarily focus on steady-state network calculations. Steady state modelling is however limited in the analysis of established systems where processes can change as affected by process upsets, shutdowns, facility upgrades, or even the development of flow assurance issues. Analyses for these types of issues require the integration of well performance information. Accurate representation of geothermal wells leads to decisions that are better informed and closer to reality. This becomes especially important for high-capital decisions involving transport and pumping facilities. This paper presents case studies on adapting commercially available steady-state transport modeling software for the integration of production or injection well performance data. It also documents the results of three case studies, results of the integrated analysis. One case study is the Tiwi WS-06 System Debottlenecking, where modeling indicated the presence of a major blockage in a steam line. The blockage was found and cleaned out, yielding a gain of 4 MWe. A second case history is the Mak-Ban Planned Shutdowns Contingency Planning, where modeling was used to plan for optimal re-routing of well flows in case of an extended shutdown of a steam separation station. A third case history is the Mak-Ban Hot Brine Injection System Optimization, wherein the model has supported cost, scope and schedule optimization of ongoing and future system improvements to ensure reliable brine injection capacity. The integrated modeling approach allowed the project teams to fully quantify the effects of system optimization for two-phase production systems. It also supported the full accounting of system-wide brine injection capacity as affected by the inter-relation of network pressures and well injection capacity as affected by pump performance and flow assurance issues.