Downhole Flowing Pressures in Geothermal Energy Production are Mainly a Function of Flowing Temperature

Abstract Similar to hydrocarbon energy production, all geothermal energy production developments will require accurate modeling of the downhole temperatures and pressures of the flowing hot steam and brine phases. In the past, traditional oil and gas-based multi-phase flow correlations/models have been used with limited success to predict the flowing pressures in steam-brine wells. The objective of this work is to unambiguously demonstrate that for a wide range of total discharge mass flow rates, the accurate modeling of flowing pressures all along a geothermal production or injection well can be achieved by relating the flowing pressures to steam and brine PVT/flow properties and the flowing temperatures via the well-known single-component, saturated steam vapor pressure tables. To prove this finding, several published actual geothermal pressure survey field datasets from different global regions (Iceland, US, Japan, etc.) are provided and their flowing pressures accurately modeling using a Dittman (1977a) modified form of the Yaws (1977) saturated steam vapor pressure tables. In addition to the steam tables, a carefully selected set of hot brine and steam PVT correlations from the geothermal literature are utilized. This wide-scale validation against numerous field measurements helps geothermal engineers to avoid the significant errors in using inapplicable oil and gas-based multiphase flow correlations/models for flowing bottom hole pressure related geothermal workflows. Indeed, for engineers involved in asset development, it is equally useful to know what to avoid as it is to know what to focus on. Technically, it is shown that by using a consistent set of saturated steam-table and fluid property correlation calculations for hot steam and brine, and accounting for the distance to flash point in real wells, that downhole flowing pressures are mainly a function of downhole temperatures in geothermal steam production of varying discharge mass flow rates. This has industry-wide significance to an improved understanding of how to manage and optimize geothermal reservoirs. This groundbreaking finding, which is a first its kind in the geothermal industry, also quantitatively supports one aspect (flowing bottom hole pressure determination) of the geothermal industry's frequent public statements that geothermal energy development is simpler than hydrocarbon energy development. The clear conclusion of this work is that as long as downhole flowing temperatures are either accurately modeled or available as measurements, so too the downhole flowing pressures will be accurately known. This allows geothermal engineers to avoid adding unnecessary uncertainties to downhole pressure calculations in geothermal wells. Geothermal production and reservoir engineers do not need any specialized multiphase flow knowledge to translate surface pressures to downhole pressures because all flowing pressures can be reliably calculated from the produced total mass flow rate, distance to flash point and flowing temperatures along the well. Very expensive downhole pressure gauges (and their high recurring maintenance costs) are not needed, and cost-effective downhole temperature gauges can be used to provide reliable calculations of downhole pressure.