Multiphase boosting is widely accepted by major oil companies. When a large-scale oil project in Algeria prioritized high reliability and safety of the whole pump system and required a single point responsibility, it looked to German manufacturer Bornemann Pumps to provide a solution. Specialists in twin-screw technology and multiphase boosting, the company was on hand to demonstrate its strength as a pump supplier and as a partner for turnkey solutions.
For an Algerian company consortium, two complete and in parallel operating multiphase pump systems were engineered, designed and manufactured to boost the production of up to 15 single wells. The wells are merged in a manifold from where the multiphase pumps transfer the flow to the next separation facility.
Multiphase boosting is widely accepted by major oil companies. During production it lowers wellhead backpressure, avoids field separation stations and achieves longer flow distances. As a consequence, flaring down of gas is no longer necessary, giving the use of multiphase pumps a positive impact on the environment.
As the multiphase pumps transfer the flow to the next separation facility from the manifold, this gives a pressure increase of 15 barg (218 psig) to 70 barg (1015 psig). The total flow was specified as being approximately 1000 m3/h per multiphase pump (154.1 MBEPD, barrels equivalent per day) having an average gas content of about 89%. The liquid viscosity was specified as being 1.0 cP. The core part of the system consists of two Bornemann multiphase pumps of the type MPC 400.
Increased efficiency
Screws with a decreasing pitch were used to increase the efficiency for the multiphase service and to substantially decrease the total costs of ownership by means of a smaller drive train and lower power consumption. The pumps are equipped with double acting mechanical seals. A Bornemann seal oil system, and a combination of API Plan 53 and 54, ensures sufficient seal oil pressure within the seals in all operational situations.
Selecting equipment
The twin-screw pump plays a major role when selecting the equipment. Its volumetric character, heavy slugging, varying water content and other typical multiphase operating challenges, makes it well suited for this purpose. Its low speed treats the fluid very sensitively, largely avoiding emulsifying oil and water; this is a definite advantage for the later separation of the phases.
A separate skid provides the base for the inlet and discharge piping for each pump. Inlet and discharge branches are both equipped with remote pneumatically operated, spring-return, fail-safe close ball valves. In case of an emergency shutdown of the entire system they also act as isolation devices. One inlet strainer is specifically designed for multiphase flow.
In order to obtain single point responsibility, for the end-user air-conditioned containers for the electric components were supplied whereby the field operator provides a main power input with 5500 V. Two transformers are used to supply the medium voltage motor with 6600 V and the auxiliary systems with 400 V, respectively, installed in a separate shelter. One control container houses the medium voltage switchboard and the medium voltage variable frequency drive. Another control container houses the main control cabinet, motor control centre for all auxiliary drives and the UPS (uninterrupted power supply) system. In case of a power failure the UPS unit supplies the necessary energy for 30 minutes in order to shut down the entire unit in a controlled sequence.
Ensuring safety
The client attached great importance to the reliability and safety of the whole pump system. In order to achieve the request a high reliable redundant PLC-system (Siemens S7–400H) was used to control the speed of the pump using the inlet pressure as reference. Even with heavy slug flow the system proved to be stable. To guarantee the highest level of safety the ESD system also consists of a redundant PLC-system (HIMA H41q) with safety level SIL3.
Bornemann also supplied the fire detection and fire fighting system for the entire pump system. All control containers are equipped with fire detectors connected to a highly reliable redundant PLC-system (HIMA H41q) with safety level SIL3 to provide the customer with the highest level of safety. In case of fire the control containers are extinguished with CO2, redundant bottle storage ensures adequate contingency reserve.
Foam carpet
The pump and piping skids are equipped with flame and gas detectors also linked to the same PLC-system. A separate extinguishing foam system is installed in a foam supply container, which provides the open nozzle system at the pump set with a foam/water mixture. This mixture creates a foam carpet over the pump set devices and suffocates the fire.
The entire pump system was subject to extensive tests and the customer witnessed factory testing prior to shipping to site. Standard acceptance tests of the single components, such as motors, frequency converters, medium voltage switch boards etc., were carried out. Multiphase pumps were tested for more than 150 hours under full load and up to a GVF of 97%. Tests were carried out on the Bornemann in-house 2.5 MW test bed.
The engineering, design and production of the pump system posed a challenge for Bornemann. Also the shipment to Algeria was a challenge. More than 16 trucks, mostly heavy load trucks, were necessary to transport the two multiphase pump systems to the harbor of Bremen. In January 2008 the pump systems arrived in the harbor of Algiers where it took a further ten days for the convoy of trucks to reach the final place of installation in the desert of Algeria.