Leakage is Management by a New Sealing System for Twin-Screw Multiphase Pumps

Abstract

Multiphase Pumping is recognised as state-of-the-art technology. But still operators and manufacturers see themselves confronted by two major challenges which are first the set of operating parameters, and second the Mean Time Between Failure. The mechanical seal system strongly contributes to the MTBF, hence this has been subject to various brainstorming with all parties involved. Modern "Multiphase Boosters" have little in common with standard pumps or compressors as far as operating parameters are concerned. All parameters especially effecting the seals are of a transient character while those in pumps or compressors are quasi-static. This paper presents a new sealing technology, which keeps any process liquid inside the pump, with emphasis on experience gained in test-bed runs and field operations. 1. Introduction There is no doubt that potential users have recognised Multiphase Pumping as a mature technology to improve oil and gas production in general. Although the current pump population is only about 250, this is spread among 50 operating companies in 25 countries around the world! Most operators are "single users", but more and more installations can be seen with "repeat" customers as well as in parallel installations. There is no doubt that whatever pump type or working principle one is looking at, this "pumping" requires no further qualification as it is based on proven performance. In its basic application at the wellhead or field header this technique requires an extreme flexibility of the boosting equipment in use. The reason being typical hydrocarbon delivery from the well, separation effects in the flow lines, or even changing conditions over the field's lifetime. Twin- Screw Multiphase Pumps have proven to be able to withstand even the toughest conditions without the assistance of flow conditioning or other auxiliary equipment. However as the mechanical seal's contribution to the Mean Time Between Failure is significant, if sometimes not the only reason for a failure, they subsequently need further development to achieve the same degree of reliability. 2. Operations Looking onto the operational envelope of either standard pumps or compressors, one thing is obvious: the operational parameters do not change substantially so their character is of a quasi-static nature, although changes may occur during e.g. day and night times. Nevertheless it is often still a challenge for the design engineer to make the equipment fit for the intended use, and at the same time incorporate the latest technological advancements and observe commercial aspects in a highly competitive market. By various reasons the user unfortunately has to take into account that equipment tends to fail, and may it only be due to Murphy's (Sod's) law: "If things can go wrong, they will." Vendors have provided equipment for a task, which was thought to be impossible only about ten years ago: to boost a mixture of liquid and gas, no matter which portions of each one looking on. Together with their customers they have jumped into an environment where operational parameters are difficult to define and sometimes even unpredictable: oil and gas production. As multiphase flow has been a challenge for engineers since decades by now, the same goes for multiphase boosting with changingsuction pressure due to varying gas volume fractions (GVF),temperatures with the above,discharge pressure with the above,mechanical impact with the above. In general we are talking of a transient flow scheme (fig. 1) in a piece of equipment which originally was not designed for this. Subsequently this offers a lot of challenges for the design engineer in charge, but for the customer as well, as he is the one to most clearly and exactly define the task to be fulfilled. There is no doubt that equipment to be used in such an environment has to be thought over from the scratch, and simple adding of auxiliaries or non-reflected use of standard components is not acceptable. Besides the technological and operational experience of the manufacturer in standard applications, which account for the solution of the majority of challenges, sub-suppliers and customers have to be tied into this with a substantial exchange of information and operational (test and field) experience. There is no doubt that sealing technology needs improvement in this respect, thanks to everyone, who has already looked into it. He has thereby improved the Mean Time Between Failure (MTBF) of this type of equipment.