A Control- and Estimation-Oriented Gravity Separator Model for Oil and Gas Applications Based upon First-Principles

Abstract

In this work, we introduce a simple model for a gravity separator based on first principles.It can be used for controller design to control the levels of oil, water and the gas pressure as well as observer design to estimate unmeasurable parameters and disturbances. Evaluation of separation efficiencies for the respective water-and oil-continuous phases are part of the model in addition. The model incorporates three dynamic state equations describing the levels of the overall liquid (water plus oil) and water as well as the gas pressure subject to the in-and outflow dynamics. Furthermore, algebraic equations calculating simplified droplet distributions for each continuous phase are introduced in order to determine the exchange of water and oil between the two continuous phases. The controllers are of PI-type and control the outflows of the separator. Additionally, we introduce a virtual monitoring approach for the inflows of gas and liquid as well as the effective split ratio of oil and water entering the continuous water phase. Measurements for these variables are either expensive, unreliable or even impossible to take (as for the split ratio). We demonstrate the results in simulations.

Optimal Operation of a Subsea Separation System Including a Coalescence Based Gravity Separator Model and a Produced Water Treatment Section

“…Besides, in the literature for first-principles based gravity separator models, the phenomenon of droplet-droplet coalescence has either been neglected [11][12][13] or modeled in a complex way. 14 The dropletdroplet coalescence is an important phenomenon in the context of gravity separation 15 and the literature is lacking a simplified way to address it. In this paper, we fill these two gaps by presenting a control and optimization oriented model that includes coalescence inside the gravity separator, and using it together with other models from literature to study how to operate the overall system optimally.…”

Evaluation of total oil and grease with flow control for mature oil fields in the context of industry 4.0

“…Othman et al (2018) make a theoreti cal and experimental investi gati on of a horizontal pipe separator, presenti ng a model that considers mixture velocity and BSW in the separati on effi ciency calculati on. Backi et al (2018) also use a simple producti on separator model for controller design and esti mati on of non-measurable parameters and disturbances. As in the Nunes (2007) model, Backi et al (2018) incorporate three dynamic state equati ons describing the levels of the global liquid (water plus oil) and water as well as the gas pressure subject to input and output dynamics.…”

“…This work is based on the models proposed by Nunes (2007), Filgueiras (2005), and Backi et al (2018). Adaptati ons were made in order to allow representati on of the producti on separators whose discharge fl ow is limited by the quality of the discarded water and not by the water-oil separati on kineti cs.…”

“…These models supported the development and optimization of control strategies. It is important to emphasize that the works of Nunes (2007), Filgueiras (2005), Silveira (2006), Ribeiro et al (2016), and Backi et al (2018), dealing with the modeling of production separators, consider the realization of interface control in the separation chamber, where all available water is separated. The control that is performed is thus efficient; however, in many cases, it is not implemented for practical reasons, as will be explained below.…”

“…This paper presents a simplified model of a primary processing unit and produced water treatment composed of a production separator and a battery of hydrocyclones. The production separator is modeled by modifying the model proposed by Nunes (2007) and Backi et al (2018). Their approach considered separators in which water-oil interface control and discharge flow were determined by the wateroil separation kinetics in the separator.…”