Gas Field Revitalisation Using Optimised Multi-Phase Pumps Installations That Can Manage Up to 100% Gas Volume Fraction, First Application in Algeria
Authors: Granado Luis E. , Drago Antonio , Smail Faycal , Khalfaoui Abdelhak , Fidanza Giovanni , Mantini Roberto 
Published: October 2019

After production startup on Lean and Rich Gas Fields in Algeria, some of the reservoirs have shown a continuous pressure decline that was affecting the real production potential of many wells, due to the surface wellhead flowing pressures approached the network pressure resulted from the central process facility (CPF) operating pressure. In this regard a "do nothing" production forecast was calculated and the results were showing that many wells would be most likely equalized with the flow line pressure within months, which is expected to casue significant production losses due to wells instability operating at critical condition, followed by eventual shut ins that will jeopardize the original production targets. Moreover, the flow regime in the pipeline network connected to the CPF was creating instability in the hydrocarbons treatment process as well.

The initial action was the installation of a Local Boosting System (LBS) at manifold level on lean gas wells, encompassing 5 compressors, connected in parallel to manage the maximum production at a given inlet pressure, compressing the volume up to 86 bar. The system was designed for lean gas with the possibility to theoretically handle all the associated liquids. In contrast, for rich gas wells a positive displacement Multi-Phase Pump was installed at well head level to confirmin the potential to lower down the flow line pressures by up to 25 bars, however the application was limited for rich gas wells only with a Gas Volume Fraction (GVF) below 95%.

Therefore, in order to have the flexibility to treat both rich and lean gas wells (up to 100% GVF), a new Multi-Phase pump system has been identified by comparing the different boosting systems performance and analyzing well by well production scenarios. The multiphase twin screw pumps are the central part of these complex systems designed to allow a wide range of operating conditions. It would be possible to decrease the suction pressure by reducing the hydrocarbon treated volume in order to manage production decline and subsequent changes on gas-liquid ratios due to further reservoir depletion. The success of this new pumps application relies on the installed liquid management system, which is designed to work together with the pumps and allowing the necessary temperature reduction whenever they reach the operating limits that would compromise the final performance and eventually halt the pumps.

With two systems successfully installed in different configurations, all the wells involved have been able to produce with an optimized bottom hole draw down to extend their productive life with the current flow line pressures constrain. In addition the stabilization of flow rate by well also brought the required stability at the CPF process. This paper is intended to provide high level technical details of the new system (liquid management and pumps) tailored to handle and treat both lean and rich gas wells, and highligh the impact on the total field production, which is the first application in Algeria and probably worldwide