TESTING THE FUNCTIONALITY OF THE OLGA SOFTWARE TO DETERMINE THE OPTIMAL MODES OF OIL TRANSPORTATION THAT PREVENT THE PRECIPITATION OF SOLID PARTICLES

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The problem of the presence of a significant concentration of the solid phase in the flow is due to the gradual destruction of the bottomhole zone with subsequent removal of particles to the surface. As these processes intensify, the risks associated with flow stability increase. The accumulation of sandy sediment creates additional hydraulic resistance, which leads to an increase in pressure, a decrease in the capacity of the pipeline network and a corresponding decrease in production. In combination with the erosive effect of particles, these factors can lead to premature wear of equipment and additional economic damage to the subsurface user. That is why a qualitative and quantitative assessment of the above processes is very important both at the design stage, when it is necessary to lay down the most optimal equipment parameters, and at the operation stage, when it is necessary to determine risks and ways to level them.

One of the solutions to such problems is the possibility of using simulators that allow you to create a detailed mathematical model from the bottom of the well to the receiving equipment with a detailed calculation of pressure and temperature losses along the entire system within a given time interval, for example, as Olga software (hereinafter referred to as Olga software) – one of the most common dynamic multiphase flow simulators.

The purpose of this work is to evaluate the functionality and effectiveness of using Olga software to solve problems related to the state of the solid phase in the flow. The research consists in:

determining the calculation methodology and the necessary initial data;
identifying the most effective process for building and analyzing a model;
conducting a series of dynamic calculations with their subsequent analysis.

The main stages of the hydrodynamic calculation were:

identification of limitations related to the presence of solid particles in the flow;
assessment of sediment formation conditions at different particle sizes;
determination of the flow rate necessary to prevent sediment formation.

FEATURES OF CALCULATING THE STATE OF SOLID PARTICLES IN A MULTIPHASE FLOW

The presence of solid particles in the flow affects the dynamic calculations of the hydrocarbon fluid flow. The additional friction of the particles against each other, against the walls of the pipeline and directly against the fluid itself creates additional pressure losses along its entire length. Depending on the phase velocities and slippage, the nature of the movement of solid particles, as well as the dynamics of their deposition on the lower forming part of the pipeline, will change.

The functionality of the software allows you to use various variables to analyze the stability of the flow in the presence of solid particles, which allows you to get a detailed idea of the nature of the flow, the dynamics of precipitation of solid particles, as well as their movement both in the flow and in the sediment itself. The most commonly used among them are sediment thickness, sediment state mode, mass flow rate and particle volume (flow, sediment, sediment + flow).

In order for the program to calculate the flow of a multiphase flow with a solid content, it is necessary to describe their characteristics and choose one of two calculation methods: SIMPLE or ADVANCED.

The main parameter describing the properties of a solid particle is its diameter. Currently, both methods allow you to enter only one diameter value to describe the entire solid phase. Also, in addition, it is necessary to specify the density, the angle of natural slope, the porosity of the sediment and the mass fraction of particles in the incoming stream. These parameters can be obtained both from relevant studies and from open sources.

The SIMPLE mode is a simplified model that allows you to take into account the movement of the solid phase in the flow and the corresponding additional pressure losses. This method is applicable for a stratified or annular flow regime, and also assumes uniform particle movement along the pipeline axis, without the possibility of estimating the parameters of sediment formation.

ADVANCED mode – allows you to reveal in more detail the processes of interaction of solid particles with a multiphase flow, taking into account their exchange in the flow between oil, water and gas. This technique is applicable for most flow regimes, and also takes into account the movement of particles both in the flow and in the formed sediment.

As part of the calculation, it is assumed that the sediment consists of two sublayers: a static part, called a fixed layer, and a movable part, called a moving layer or sediment (Fig. 1). The rate of particle deposition determines the size of the sediment, while its porosity determines the amount of liquid trapped in the layer. It is important to note that the flow of liquid through the stationary part of the sediment is not taken into account.

 

Figure 1. Layers of solid particles sediment

Depending on the balance of forces acting on solid particles in the formed sediment (gravity, lifting force, friction force, etc.), it can be in one of three states: static, mobile and weighted. In a static state, friction forces prevail, which makes it impossible for solid particles to move. The mobile state implies the movement of the upper layers of the sediment, in which the lifting forces are still insufficient to carry the particles into the main stream. In the suspended state, the lifting forces ensure the removal of solid particles from the formed sediment, which leads to their penetration into the moving fluid layers.

ANALYSIS AND SYSTEMATIZATION OF THE SOURCE DATA

It is no secret that the accuracy and predictive ability of a mathematical model directly depend on the quality of the source data, and first of all, on the conditions of laboratory research, therefore their preparation and analysis are an important stage in modeling.

As part of the construction of a model to assess the dynamics of solid particle deposition in a multiphase flow in the conditions of deposit N, the following modeling stages can be distinguished:

Building a pipeline model

In this work, one of the oil collecting reservoirs of the field N Dn =159× 10mm, L = 1600 m was adopted as the pipeline under study, the products of which are collected from 16 wells and transported further to the GZU.

In addition to the total length and internal diameter, a detailed pipeline profile was used to calculate the hydraulics, which allowed for additional resistance associated with the terrain (Fig. 2).

 

Figure 2. Location and profile of the pipeline in the collection network model

Reproduction of fluid properties

When modeling the fluid, laboratory studies were used as the main initial data to determine the component composition and physico-chemical properties, which, together with the equations of state of PVT packages, made it possible to reproduce the phase diagram (Fig. 3), thereby determining the regions of the multiphase and single-phase state of the fluid.

In addition, the fluid was adjusted to the actual viscosity values of the degassed oil. In the right figure 3, the red dots correspond to the actual (laboratory) values of the viscosity of the fluid at various temperatures, the blue line is the initial reproduction of the viscosity of the PVT package, the yellow line is the viscosity values after appropriate adjustment. Thus, it can be seen from the graph that after setting up the fluid, it was possible to reproduce the laboratory research data as accurately as possible, which made it possible to use the fluid model as close to reality as possible in the future.

 

Figure 3. Reproduction and adjustment of fluid properties

Description of the parameters of solid particles

According to laboratory studies, the granulometric composition of sediment samples taken at the deposit is represented by particles with a diameter of 1.5 to 400 microns. Due to the fact that the solid deposition model in the program uses one value as the diameter, the resulting range had to be reduced to a single value. Since the values of the extreme values differed from each other by more than 250 times, the calculation of the arithmetic mean was considered impractical. To determine a single value and more correct averaging, a weighted average was used, in which the corresponding proportion in the total composition was used as the weight of each diameter. Thus, a single particle size is accepted as a weighted average and equal to 104 microns.

Also, the following average parameters are used to calculate the deposition of solid particles:

particle density 2100 kg/m3;
the angle of the natural slope is 30°;
the porosity of the sediment is 0.35.

 

Figure 4. Granulometric composition of the sediment of the reservoir under consideration

Determination of initial and boundary conditions of modeling

As part of the pipeline capacity assessment, 4 variants of the system operation with total flow rates of 200, 300, 400 and 500 m3/day were considered. In order to reproduce the most unfavorable scenario of sand removal from the face, it was decided to take into account the mass concentration of the solid phase in the stream equal to 10%. A dynamic calculation with a duration of 24 hours was carried out for each flow option. This duration is set based on the need to enter the steady-state operation of the system and the subsequent correct assessment of the calculated parameters.

As the boundary conditions of the system for all scenarios, the pressure at the outlet of the pipeline Rvh = 1.2 atm, the fluid temperature at the inlet Tvh = 36 ° C and the ambient temperature equal to 20 °C. were set. Thus, by recording the fluid flow rate and outlet pressure, the required inlet pressure was determined to ensure an appropriate flow rate.

SIMULATION RESULTS
To determine the limitations associated with the presence of solid particles in the flow, an assessment of the risks of sand sediment formation in the pipeline under consideration at various fluid flow rates was carried out. Since the granulometric composition of the removed sand is represented by a fairly wide range of diameters, it was decided to carry out an additional series of calculations involving an increase of 50% in order to simulate the flow behavior with deterioration of the characteristics of the removed sand. Comparison of simulation results with weighted average and increased diameter (Table. 1) allowed us to obtain a more complete picture of the conditions necessary for the removal of sandy sediment.
Within the framework of dynamic calculations, first of all, the intensity and localization of precipitation sites under various scenarios were determined. The comparison was made based on the results of a 24-hour simulation of the system. The thicknesses of the formed sediment, the total mass of the solid phase in the pipeline and the mass flow rate of particles at the outlet of the system were compared (Fig. 5-10). A detailed description of the results is discussed below.
Table 1. Summary calculation results with particle sizes equal to 0.1 mm and 0.15 mm

Particle diameter, mm	Flow rate, m3/day	Maximum sediment thickness, mm	Solid phase mass, kg	Maximum mass flow rate, kg/s
0,1	200	34	200	-
	300	30	300	-
	400	3	15	0,055
	500	1	7	0,04
0,15	200	37	200	-
	300	24	300	-
	400	18	245	0,1
	500	10	55	0,085

 

 

1. The particle diameter is 104 microns
As can be seen from the graphs (Fig. 5-7), active precipitation occurs at flow rates from 200 to 300 m3/day. At the same time, its localization (the first 500 meters and a depression at a distance of 1100 meters) is due to the relatively low flow velocity and geometry of the pipeline. It is also worth noting that for these costs, within the framework of a 24-hour calculation, there is a constant accumulation of solid phase in the pipeline with zero solid phase flow at the outlet.
Starting from a flow rate of 400 m3/day, the flow reaches a sufficient velocity to carry out particles with a diameter of 0.1 mm without significant accumulation in the pipeline in question. Accordingly, by maintaining the flow rate above this value, intensive precipitation can be avoided.
According to the solid phase mass flow schedule (Fig. 7), sand removal at a flow rate of 400 to 500 m3/day occurs unevenly. This indicates that the solid phase is transported in the mode of mobile sediment, which periodically accumulates in a sandy "plug", is carried away by the flow and is removed from the pipeline.

Symbols:
black line – pipeline profile;
sediment thickness profile: red line – at a flow rate of 200 m3/day; blue – at a flow rate of 300 m3/day; green – at a flow rate of 400 m3/day; brown – at a flow rate of 500 m3/day
Figure 5. Profile of the thickness of the sandy sediment modeling during 24 hours

Symbols:
red – 200 m3/day; blue – 300 m3/day; green – 400 m3/day; brown – 500 m3/day
Figure 6. Dynamics of accumulation of solid particles with a diameter of 0.1 mm in the pipeline at various flow rates

Symbols:
red – 200 m3/day, blue – 300 m3/day, green – 400 m3/day, brown – 500 m3/day
Figure 7. Dynamics of solid phase mass flow (0.1 mm) at the outlet of the pipeline at different fluid flow rates
2. The particle diameter is 150 microns
According to the calculation results (Fig. 8-10), active precipitation occurs at flow rates from 200 to 400 m3/day. At the same time, the localization is similar to the cases discussed earlier – the first 500 meters of the pipeline, as well as a depression at a distance of 1100 meters.
For expenses of less than 300 m3/day, there is a constant accumulation of solid phase in the pipeline without sand removal within the framework of a 24-hour calculation.
At a flow rate of 400 m3/day, active precipitation and accumulation of sediment occurs during the first 16 hours, after which its amount stabilizes and reaches a steady state, as evidenced by the graphs of mass flow (Figure 8) and the dynamics of solid phase accumulation in the pipeline (Figure 9).
Starting from a flow rate of 500 m3/day, the flow reaches a sufficient velocity to carry out particles with a diameter of 0.15 mm without significant accumulation in the pipeline in question. Accordingly, by maintaining the flow rate above this value, intensive precipitation can be avoided.
According to the solid phase mass flow schedule, sand removal at flow rates from 400 to 500 m3/day occurs unevenly (Fig. 10). This indicates that the solid phase is transported in the mode of mobile sediment, which periodically accumulates in a sandy "plug", is carried away by the flow and is removed from the pipeline. In addition, it is possible to note periods of accumulation when the mass consumption of the solid phase is practically absent.

Legend:
black line – pipeline profile;
sediment thickness profile: red line – at a flow rate of 200 m3/day; blue – at a flow rate of 300 m3/day; green – at a flow rate of 400 m3/day; brown – at a flow rate of 500 m3/day
Figure 8. Profile of the thickness of the sandy sediment modeling for 24 hours

Symbols:
red – 200 m3/day; blue – 300 m3/day; green – 400 m3/day; brown – 500 m3/day
Figure 9. Dynamics of accumulation of solid particles with a diameter of 0.15 mm in the pipeline at various costs

Symbols:
red – 200 m3/day; blue – 300 m3/day; green – 400 m3/day; brown – 500 m3/day
Figure 10. Dynamics of the mass flow rate of the solid phase (0.15 mm) at the outlet of the pipeline at different liquid flow rates

CONCLUSION
In this work, the functional capabilities of specialized software for solving problems related to modeling a multiphase flow with a solid content were evaluated.
The program made it possible to calculate the dynamic system for various values of the diameter of solid particles in a multiphase flow and solve the task of evaluating the dynamics of solid phase accumulation in the pipeline and determining the fluid flow rate necessary for the removal of solid particles.
The program is applicable for the implementation of simulation modeling in the formation of technical solutions in order to minimize the risks of operating linear ground infrastructure facilities.

About the authors

Murat Usenovich Yerlepessov

Филиал ТОО "КМГ Инжиниринг" "КазНИПИмунайгаз"

Email: m.yerlepessov@kmge.kz

эксперт Службы системы сбора, транспортировки и подготовки продукции Департамента техники и технологии добычи нефти и газа

Kazakhstan

Oleg Igorevich Zaytsev

Email: OZaitcev2@slb.com

ведущий инженер по добыче компании «Шлюмберже» (Schlumberger)

Abay Almatayevich Yermekov

Email: A.Yermekov@kmge.kz

руководитель службы системы сбора, транспортировки и подготовки продукции ТОО «КМГ Инжиниринг», филиал «КазНИПИмунайгаз»

Sain Kubeysinovich Amirov

Филиал ТОО "КМГ Инжиниринг" "КазНИПИмунайгаз"

Author for correspondence.
Email: s.amirov@kmge.kz

ведущий инженер Службы системы сбора, транспортировки и подготовки продукции Департамента техники и технологии добычи нефти и газа

Kazakhstan

Zhuginis Sytdyykhovich Urbisinov

Email: Zh.Urbissinov@kmge.kz

старший инженер службы информационного обеспечения ТОО «КМГ Инжиниринг», филиал «КазНИПИмунайгаз»

References

Supplementary files