OUR CUSTOMER HAS oilfieldswhich are relatively old and haveproduced oil and gas for manyyears. Over time the natural

reservoir pressure has dropped off to a pointwhere some wells are no longer able toovercome the back pressure generated bythe surface flow lines and the first stageseparator of the process facility.

The conventional alternatives consideredby the operator would be increasing the flowline size and install a low pressure first stageseparator which would be significantly larger.These alternatives were carefully reviewed,however, it turned out that the costs andnecessary permissions by the appropriateauthorities would have been significant andnot economical.

Then in early 2015 the company heardabout multiphase pumping. This moreeconomic alternative caught the interest ofthe management as the production wasexpected to remain interesting for years to come.

A contact was established with Leistritz and a project study wasinitialised. The target of the study was to draw down the back pressureon the producing wells with the help of a multiphase wellhead pumpingsystem to about 200 PSIG, which would allow all the wells to produceat an acceptable rate. To overcome the flow line pressure includingsome reserve, the pressure boosting of the multiphase pump had to bearound 500 PSIin order to reach the line back pressure of 700 PSIG.The Multiphase Wellhead System (Model L300) based on the Leistritztwin-screw pump was selected, proposed and purchased in thesummer of 2015.

The system had to be designed for remote unmanned operation,and outside of power supply had to be completely self-supporting.Remote access of the operating parameters was achieved over theInternet by a secure access for the operator as well as for Leistritz.

The liquid rates could vary between 300 to 1,000 BLPD and gasrates between 0.5 and one million SCFD. The combined flow rate atpump inlet conditions would be between 6,000 and 14,000 BPDe

(barrels per day equivalent) corresponding to a GVF (gas void fraction)around 95 per cent. The flow regime was expected to be slug flow, andheavy slugs could affect the multiphase pump unit. In order to seal andprotect the pump and remove the heat of compression from the pumpa recirculation system was included, designed to gather liquids in aknock-out boot or separator downstream of the pump and circulatesome of the liquids back to the pump suction. This system wouldassist the pump and provide the liquids necessary to maintaincompression even during longer gas slugs.

Other design features included a VFD controlled 400 HP 1,800 RPMelectric motor and a double mechanical seal system with the API Plan54 seal flush. The complete unit with piping, valves, instrumentationand controls was designed and manufactured in the Leistritz facilities.Installation and commissioning took place in Q2 of 2016. The unit hasperformed as expected and adding significant production for theoperator.

This case study points to the opportunities for using multiphasepumping in lieu of other back pressure reducing alternatives. Themultiphase pump together with VFD speed control has shown itsflexibility in instantly adopting to actual field conditions and optimisingproduction with lower flowing wellhead pressure. One of the greatfeatures with the twin-screw multiphase pump is that pressure boostingis independent of inlet pressure, giving the operator the best possibletools to produce ageing and low energy reservoirs. n

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The Leistritz multiphase pump has helped to boost production in ageing and low energy wells

Leistritz has successfully installed a multiphase pump to lower field pressure, allowing lowenergy wells to come back into production. Sven Olsen, senior consultant, Leistritz AdvancedTechnologies, shares the story of how the project has been completed.

Optimising production with

multiphase pumping

This case study points to theopportunities for using multiphasepumping in lieu of other back pressurereducing alternatives”

Technology

60 oilreview.me Issue 7 2017