Patent Application
20220136636
The present disclosure relates to dewatering flowlines. More particularly, the present disclosure relates to dewatering subsea flowlines such as gas flowlines prior to commissioning.
For subsea applications, hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well through a subsea wellhead system that penetrates the hydrocarbon-bearing geologic formation. In subsea applications, various types of infrastructure may be positioned along a sea floor and coupled by flow lines. The flow lines enable flow of production fluids, e.g., oil, gas, or other types of production fluids, from one subsea installation to another. Flow lines also may extend upwardly to various types of surface facilities, such as surface vessels or platforms.
Upon commissioning of a gas flowline, a known method to dewater is to insert a pipeline inspection gauge (referred to as a “pig”) train in the far, or lower end of the water flooded flowline. A gas line from shoreside or vessel compression facility is connected to the lower of the flowline. Then compressed gas, typically nitrogen, is driving a pig train from subsea and back to shore, or alternatively, in the reverse direction. The gas pressure should be slightly higher than that of the ambient seawater pressure to drive the pig towards shore. For deepwater flowlines that can mean a requirement of 2-300 bars, which governs a requirement for an extensive compression plant due to the large pressure ratio. This process might be cumbersome, expensive and time consuming.
As the market for offshore gas is picking up, an increased amount of such flowlines is expected. Hence, the operators are looking for more efficient ways to execute this operation.
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining or limiting the scope of the claimed subject matter as set forth in the claims.
According to some embodiments, a subsea fluid flowline dewatering system is described. The system includes: at least one multiphase pump positioned at lower end of a flowline to be dewatered; and a pig train configured to be introduced at an upper end of the flowline, the multiphase pump being configured to provide suction at the lower end of the flowline thereby supporting downward travel of the pig train towards the lower end of the pipeline. According to some embodiments, the fluid flowline is gas flowline.
According to some embodiments, the multiphase pump is configured to process fluids at least 10% gas volume fraction (GVF). According to some embodiments, the multiphase pump is configured to process fluids at least 30% gas volume fraction (GVF). According to some embodiments, the multiphase pump is configured to process fluids at least 50% gas volume fraction (GVF).
According to some embodiments, the system further includes a meter for density detection to estimate GVF, and a flow mixer unit positioned upstream of the meter. The mixer unit is configured to mix gas and liquid phases of fluid to enable adequate GVF estimations from the meter.
According to some embodiments, in applications where the lower end is greater than 1500 or 2000 meters below the upper end, a second pump positioned in series with and downstream of the multiphase pump. According to some embodiments, the second pump is a single phase pump configured to process fluids less than about 10% GVF.
According to some embodiments, the system also includes a controllable sea water inlet positioned up stream of the multiphase pump, the sea water inlet including a choke valve that is configured to allow additional sea water into the fluid entering the multiphase pump to ensure the GVF is not greater than the multiphase pump can adequately handle.
According to some embodiments, a method is also described to dewater a subsea gas flowline having an upper end and a lower end. The method includes launching a pig train at the upper end and pumping with a multiphase pump positioned at the lower end thereby supporting downward travel of the pig train towards the lower end.
The subject disclosure is further described in the following detailed description, and the accompanying drawings and schematics of non-limiting embodiments of the subject disclosure. The features depicted in the figures are not necessarily shown to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form, and some details of elements may not be shown in the interest of clarity and conciseness.
One or more specific embodiments of the present disclosure will be described below. The particulars shown herein are by way of example, and for purposes of illustrative discussion of the embodiments of the subject disclosure only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the subject disclosure. In this regard, no attempt is made to show structural details of the subject disclosure in more detail than is necessary for the fundamental understanding of the subject disclosure, the description taken with the drawings making apparent to those skilled in the art how the several forms of the subject disclosure may be embodied in practice. Additionally, in an effort to provide a concise description of these exemplary embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” Also, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is intended to mean either an indirect or a direct interaction between the elements described. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. The use of “top,” “bottom,” “above,” “below,” and variations of these terms is made for convenience, but does not require any particular orientation of the components.
Certain terms are used throughout the description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name, but not function.
In the drawings and description that follow, like parts are typically marked throughout the specification and drawings with the same reference numerals. The drawing figures are not necessarily to scale. Certain features of the disclosed embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present disclosure is susceptible to embodiments of different forms. Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure and is not intended to limit the disclosure to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results.
As a certain amount of gas will leak across the pig train (not shown), some gas is to be expected to pass through the multiphase pump 250. According to some embodiments, flow mixer 240 and multiphase flowmeter 242 or another device for density detection is provided used to estimate Gas Volume Fraction (GVF). When the GVF exceeds the maximum acceptable for the pump, the intake choke 236 may be opened to let seawater into the suction side 238. Hence, the pump 250 will be able to generate a differential pressure enabling to dewater the flowline, even when high gas content is to be evacuated towards the end of the dewatering process. According to some embodiments, multiphase pump 250 is configured to handle GVF of up to about 30%. In such cases the choke 236 is used to ensure the GVF entering pump 250 is not greater than 30%. According to some embodiments, multiphase pump 250 may be configured to handle a different amount of maximum GVF. For example, according to some embodiments, pump 250 is configured to handle GFV of up to about 10%, and according to some other embodiments, pump 250 is configured to handle GFV of up to about 50%.
The system described is relatively compact compared to known systems and could be installed on a temporary structure. According to some embodiments, the dewatering might be a continuous operation with no need for cyclic operation to evacuate gas from separators. In contrast, systems that are configured with one or more single phase pumps instead of a multiphase pump, rely on one or more subsea separation units. With such arrangements, eventually the separator units will fill with water and the dewatering process needs to be interrupted while the water is removed from the separator(s). The systems as configured as shown herein will not need to be uninterrupted since such systems use a multiphase pump. Dewatering of flowlines using arrangements according to embodiments may be done with less topside compression power, more energy efficiency and potentially be faster and safer. The final gas pressure in the flowline will be lower as well, which will ease the subsequent de-pressurizing.
According to some embodiments, pumps 250 and 350 are powered from a vessel 160 via cable 162. According to some embodiments, pumping is occurring at the differential pressures required when water depths exceed 1500 to 2000 meters, pump 350 is a booster stage, which is added to multiphase pump 250. The multiphase pump 250 will compress the associated gas and in some examples is configured to handle up to about 30% GVF, while the booster stage 350 is a single-phase pump that is configured to handle up to about 10% GVF. According to some embodiments, multiphase pumps 250 and 350 may be configured to handle different amounts of maximum GVF. For example, according to some embodiments, single-phase pump booster stage 350 may be of a design that can handle a maximum GVF lower than 10%.
According to some embodiments, pumps 250 and 350 are started with a fully open sea water intake choke 236. As the desired speed is reached and the intake choke 236 is throttled down, the pump will start to draw down pressure on the suction side 238. The inlet check valve 234 will crack open and the dewatering process starts.
As a certain amount of gas will leak across the pig train, some gas is to be expected through the pump 250. A multiphase flowmeter 242 or another device for density detection is used to estimate GVF. When the GVF exceeds the maximum acceptable for the pump 250, the intake choke 236 will start to let seawater into the suction side. Hence, the pump 350 will be able to generate a differential pressure to dewater the flowline, even when high gas content is to be evacuated towards the end of the dewatering process.
The above discussion is meant to be illustrative of the principles and various embodiments of the present disclosure. While certain embodiments have been shown and described, modifications thereof may be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described herein are exemplary only and are not limiting. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims that follow, that scope including all equivalents of the subject matter of the claims.
This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 17/366,312, filed Jul. 2, 2021, which claims benefit of U.S. Provisional Patent Application Ser. No. 63/047,592, filed Jul. 2, 2020. Each of the aforementioned related patent applications is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63047592 | Jul 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17366312 | Jul 2021 | US |
| Child | 17574246 | US |
