Methodology for optimizing pipeline route selection, separator and power plant placement in geothermal projects – case of Olkaria IV in Kenya

Abstract

The objective of this study is to create a tool and develop a methodology for optimizing pipeline route selection, placement of separators and power plants in geothermal projects. The process usually faces a number of constraining challenges including environmental protection issues, land use policies and technical requirements. Among the technical constraints considered are pressure drop along the pipeline, flow regimes, pipeline diameter, thickness and length, maximum allowable gradients and associated costs for each component. The pipe diameter, thickness and overall length have a great bearing on the total pipeline cost. An optimized route and pipe diameter will directly lead to an optimized project cost that is the drive for this study. Variable topography distance transform (VTDT) method was used to define the routes and weighted variable topography distance transform (WVTDT) to find best location for the separators and the power plant. Application of constraints was used to optimize the pipe network and flow in each pipe.

VTDT is based on the chamfer metric distance transform algorithm which works with the digital elevation matrix (DEM) to get height values for each cell. For this study the DEM and field data for Olkaria IV geothermal field were used to test the model. The study has shown that good results are obtained with VTDT for route selection, separator and plant location optimization. The study also proposes a sequence of optimization steps where the separator location is first optimized taking into account the location of production wells and hot reinjection wells. Cold reinjection wells are not considered since the pipes are usually made of polyethylene whose price is much lower compared to the price of steel used for other pipelines. The length of the routes from each well to the separator is then determined. This is followed by optimizing the plant location considering the already optimized separator locations. In this study, the use of WVTDT shows that the length of the pipeline can be shortened by 1542 m. It is, however, important to conduct a detailed survey of the area to map out all the coordinates of the no-go zones as defined by human, technical or environmental constraints for inclusion in the program as constraints.