RU2683336C1 - Hydrates formation processes in the production flowlines monitoring method - Google Patents

Abstract

FIELD: gas production industry.

SUBSTANCE: invention relates to the field of natural gas production and can be used for the hydrates formation beginning process and the potential hydrate plug place in the production flowlines determining. Essence of the hydrates formation processes in the production flowlines monitoring method consists in the scanning pressure wave periodical generation at the flowline end and the reflected signal subsequent fixation and analysis. During the method implementation for the cleaned flowline, obtaining the reference echogram, determining the characteristic points and areas, including the reference section thereon. Using the working echograms in the monitoring process, determining the pressure wave velocity at the flowline reference section. Comparing the working echograms against each other and against the reference echogram, detecting the reflected signal abnormalities, referencing the anomalies to the pipeline diagram and making conclusion about the new local resistance formation beginning. Considering the working echograms time parameters, calculating the absolute gas temperature T_n in the new local resistance vicinity at section n by the recurrence formula

, where T_n-1 is the absolute temperature on the preceding the n section n-1 characteristic section; ΔL_n and ΔL_n-1 are the n and n-1 characteristic sections lengths; Δt_n and Δt_n-1 is time of scanning wave passage of characteristic sections n and n-1. By the pressure values at the well and in the off switching valves building calculating the pressure in the new local resistance vicinity. After which, determining the possibility of the crystalline hydrates existence under the said thermobaric conditions in the vicinity of new local resistance. Scanning pressure wave is created by the valve opening or closing on the flowline in the switching valves building with possible use of low- or high-pressure receiver and with periodicity in range of 0.5…1.5 h depending on the gas in the flowline temperature and the working echograms anomalies dynamics.

EFFECT: object of the invention is the hydrate plugs possible formation place determining and reduction of the system installation costs by using of the gas complex treatment plants already operating standard equipment.

7 cl, 11 dwg

Description

The invention relates to the field of natural gas production and can be used to determine the beginning of the hydrate formation process and the location of a potential hydrate plug in pipelines for pumping gas from the wellhead to the building of switching valves (ZPA) of the complex gas treatment unit (GPP).

In the Far North, gas production may result in technological complications with the formation of hydrates in the pipelines-plumes from the wellhead to the ZPA [Prakhova M.Yu., Krasnov AN, Khoroshavina EA, Shalovnikov EA Methods and means of preventing hydrate formation at gas production facilities // Oil and Gas Business. 2016. No1. S. 101-118]. To determine the processes of hydrate formation in pipelines, a method for controlling the temperature of a gas is known [Istomin V.A., Kvon V.G. Prevention and elimination of gas hydrates in gas production systems. M .: IRC Gazprom LLC, 2004], a method of controlling the difference between the calculated gas temperature at the ZPA (according to the gas temperature at the wellhead and the ambient temperature) and the actual (measured) gas temperature at the ZPA [Patent RU2 329 371. Control method the process of hydrate formation prevention in infield plumes of gas and gas condensate fields of the Far North / Andreev O.P., Salikhov Z.S., Akhmetshin BS and etc.]. These methods are characterized by the determination of signs of the onset of hydrate formation, but there is no possibility of determining the place in the loop. In addition, the inertia of the detection time is characteristic in the case of flows with low linear velocities.

There is also a known method for determining the potential site of the onset of hydrate formation processes based on monitoring deviations in the dynamics of the measured and calculated gas temperatures, supplemented by monitoring the pressure at the wellhead [Patent RU 2573654. Method for controlling the process of preventing hydrate formation in gas gathering plumes connected to a common reservoir in gas and gas condensate fields of the Extreme North / Arno O.B., Arabsky A.K., Akhmetshin B.S. and etc.]. This method is possible to use at sites with connecting wells through gas collection plumes to the gas collection manifold. When the conditions for hydrate formation start are fulfilled, the analysis of the pressure change at the wellhead connected to this reservoir begins, and the hydrate formation section is determined as the maximum pressure is approached. This method allows you to localize a potentially emergency loop, if there is an increase in pressure on one or a group of wells connected to the same loop, or to identify a potentially emergency section of the reservoir, if the pressure rises at once for several groups of wells. However, this method has a low possibility of localization: the plume sections can be quite long, not to mention the collector. In case of emergency liquidation of the hydrate plug, this information may not be enough to quickly solve the problem.

The closest analogue to the achieved result is a method for monitoring flow parameters in a pipeline in order to register hydrate formation. [WO 00/46545 Method and device for monitoring flow parameters in a pipeline in order to register hydrate formation. / BAKKE, Knut, I]. This method involves the emission of circular or linear polarized electromagnetic waves at one or a group of frequencies into the pipeline, registration of reflected waves and the reflection wave time from the reflected wave, determining the coordinates of the reflection point, and also, using the dielectric constant, determining the substance that served as the reflection point.

This method allows you to determine the place of formation of a local disturbance, which served as a reflection point, and allows you to judge the substance that precipitated by the dielectric constant. However, the selectivity of this definition substantially depends on the accuracy of measuring the dielectric constant, which, in the presence of imperfections in the structure and shape of the precipitated substance, may be insufficient.

This method is applicable only to pipelines in the design of which there are no turns, bends or a number of bends at right angles, i.e. mainly in offshore field pipelines, as electromagnetic waves with the least attenuation propagate rectilinearly. However, ground loops have a considerable length and can be subject to significant temperature extremes, as a result of which thermal compensators are used in their design - U-shaped sections of the pipeline that can limit the propagation of electromagnetic waves in the loop, which makes the prototype method not applicable for long ground loops, especially in the Far North.

In the prototype method there is no possibility of predicting the processes of hydrate formation and ice formation, since it captures only already formed deposits of ice and hydrates.

In addition, in order to fulfill the declared capabilities, it is necessary to install a specially prepared section of the pipeline, similar in diameter to the operating loop, which entails significant economic costs for the manufacture, delivery and capital work on the pipeline. Installation work may require the need to stop gas production from the bushes during the installation of this section, which, in turn, is associated with economic losses from underloading of gas treatment plants.

The objective of the invention is to determine the location of the possible formation of hydrate plugs and reduce the cost of installing the system by using the standard equipment of the integrated gas treatment plants that is already in operation.

The essence of the proposed method for monitoring hydrate formation processes in fishing plumes consists in periodically generating a scanning wave at the end of the plume, fixing and analyzing the reflected signal.

In contrast to the prototype in the proposed method, the inner surface of the examined loop is cleaned, an exemplary echogram is obtained for it, and characteristic points are determined on it, corresponding to the local resistance of the pipeline forming the response signal. Characteristic sections are distinguished between adjacent characteristic points, one of which is taken as a reference.

In the process of monitoring periodically create a scanning pressure wave (SVD), receive response signals in the form of echograms.

The propagation speed of the scanning wave is determined from the transit time of the SVD reference plot,

By comparing the obtained echograms with a reference one, abnormal changes in the reflected signal in amplitude are detected. If they are available, they are tied to the piping scheme and the type of local resistance, the dynamics of the reflected signal amplitude changes at the obtained characteristic points of the pipeline are analyzed, and a conclusion is drawn about the formation of a new local resistance.

The absolute gas temperature T _n in the vicinity of the new local resistance in section n is calculated from the change in the travel time of the characteristic wave and the gas temperature at the end of the plume by the recurrence formula

,

,

where T _n-1 is the absolute temperature in the characteristic region n-1 preceding the region n, ΔL _n and ΔL _n-1 are the lengths of the characteristic regions n and n-1, respectively, Δt _n and Δt _n-1 are the travel times of the scanning wave characteristic sites n and n-1, respectively.

The gas pressure at the ZPA and wellhead is constantly measured and the pressure in the vicinity of the new local resistance is calculated from their ratio.

The possibility of the existence of crystalline hydrates under given thermobaric conditions in the vicinity of the new local resistance is determined by the diagram of three-phase equilibria for hydrate-forming gases.

A scanning pressure wave is generated in several ways:

- close the crane on the loop in the ZPA;

- stop the flow of gas to equalize the pressure in front of the tap in the ZPA to the wellhead pressure and open the tap;

- use a low pressure receiver (RND), stop the gas flow on the loop, release gas into the receiver, close the tap;

- use a high pressure receiver (RVD), in which the compressor is pre-pumped gas to a pressure higher than the gas pressure in the loop, stop the gas flow on the loop and release gas from the receiver into the loop.

- use the HPP, which is filled with gas from the discharge line at the outlet of the booster compressor station.

The frequency of generation of the SVD is chosen in the range of 0.5 ... 1.5 hours depending on the gas temperature in the loop and the dynamics of the amplitude of the reflected signal at characteristic points of the echogram.

In FIG. Figure 1 shows the temperature distribution T _n in characteristic plume sections.

In FIG. 2 shows the curves of three-phase equilibria for individual hydrate-forming gases [Istomin V.A., Kvon V.G. Prevention and elimination of gas hydrates in gas production systems. M .: OOO IRC Gazprom, 2004].

In FIG. Figure 3 shows the generation of SVD using flow energy. In FIG. 4 shows a plan for connecting loops to a common collector. In FIG. 5 shows the generation of SVD due to external energy. In FIG. 6 shows an echogram of the studied plume. In FIG. 7 shows an echogram with reference to the characteristic points of the loop.

In FIG. 8 shows a fragment of the circuit of the studied loop.

In FIG. Figure 9 shows the change in the echogram with decreasing temperature in the loop as compared with the reference echogram.

In FIG. 10 shows an echogram with increasing amplitude of the reflected signal from the characteristic point of the loop

In FIG. 11 shows an echogram with the formation of a new local resistance in the loop.

This method is advisable to use primarily in gas production fields with a collector-cluster gas collection scheme. With this method of production, gas from the wells of one bush is pumped to the ZPA via a loop. In the process of transportation along the train, various technological complications may arise, including the formation of hydrate and ice plugs.

To determine the place of formation of a new deposit, the echolocation method is used: the distance is determined by the delay time of the scanning pressure wave (SVD) reflected from the obstacle. Before using the method, the inner surface of the loop is cleaned of accumulated deposits by blowing on a candle or otherwise.

The first measurement gives an echogram for a clean pipeline. It is taken as a model. Using the pipeline passport, characteristic points corresponding to the structural elements of the pipeline forming the response signal are determined on it: turns, elbows, etc.

Further measurements are repeated in a systematic manner. To determine the propagation velocity of the wave, a reference plume section is distinguished: a section with characteristic points to which the distance is known and which give a well-defined by the shape of the signal and time-stable reflection of the LED. This site is more appropriate to choose closer to the ZPA. Based on the reflection time from the data of the characteristic points, the calculated wave propagation velocity for each scanning session is determined.

Each new echogram is stored in a database and used as a basis for analysis and interpretation of the technological situation in the pipeline. The echogram obtained in the current scanning session is compared with the exemplary echogram and the abnormal changes in the signal in amplitude are detected both from the already identified characteristic points (design features of the loop) and from new formations. New formations are localized by the location between the characteristic points.

Then, an analysis of the dynamics reflected from characteristic points is carried out using the generated base of echograms and a conclusion is made about the process of deposit growth.

The train is divided into characteristic sections - sections between characteristic points tied to the structure of the train. For the general case, the number of sections is taken equal to N. For the zero characteristic point, the installation location of the reflected light detection sensor is considered. To describe the order in which the temperature is found in the characteristic region under an arbitrary number n, the first characteristic region is taken as the reference region — the region between the characteristic point N ₁ and the reflected wave detection sensor (characteristic point N ₀ ) (Fig. 8).

The speed of sound in gases, which is equal to the speed of propagation of SVD, depends on temperature [6] through the ratio:

where ν is the speed of sound in a gas, γ is the ratio of the heat capacity of gas at constant pressure to heat capacity at constant volume, R is the universal gas constant, T is the absolute temperature of the gas in Kelvin, μ is the mole mass, numerically equal to the molecular weight of the gas. In this way:

The speed of sound in a characteristic plot No. 1 is calculated by the formula:

,

,

where L ₁ -L ₀ - the length of the characteristic section, expressed through the difference in distances from the detection sensor of the reflected waves to the characteristic points N ₁ and N ₀ ; t ₁ -t ₀ is the travel time of the SVD of a characteristic section, expressed in terms of the time difference from the moment of generation of the SVD to the detection of reflected signals from characteristic points N ₁ and N ₀ . In this particular case, L ₀ = 0 m and t ₀ = 0 s.

Then the temperature in the area between these reference points:

.

.

This gas temperature T ₁ is measured at the end of the loop.

For the general case:

.

.

For the convenience of calculations, we introduce the proportionality coefficient K:

.

.

This coefficient is calculated for the reference plot according to empirical data:

.

.

We assume that the coefficient K within the adjacent characteristic sections does not change or changes slightly, i.e.:

or

,

,

,

,

Will accept

ΔL _n = L _n -Z _n-1 - the length of the n-th characteristic section,

ΔL _n-1 = L _n-1 -L _n-2 - the length of the n-1 characteristic section,

Δt _n = t _n -t _n-1 is the transit time of the SVD of the n-th characteristic section,

Δt _n-1 = t _n-1 -t _n-2 is the transit time of the SVD of the n-1st characteristic section.

Then:

.

.

The temperature at an arbitrary nth characteristic region (n≥2) is calculated by the generalized recurrence formula:

Thus, when a new local resistance appears on the nth characteristic site, the temperature in its vicinity is calculated.

The pressure in the vicinity of the new local resistance is calculated from the pressure values at the wellhead and at the end of the loop according to one of the known models of pressure distribution along the pipeline.

The obtained thermobaric conditions in the vicinity of the new local resistance are compared with the thermobaric conditions for the existence of hydrates according to the three-phase equilibrium diagram for hydrate-forming gases (Fig. 2), which are part of the produced gas. If the conditions satisfy the conditions for the existence of hydrates, make a conclusion about the potential existence of hydrates in the loop at the site of the new local resistance.

Several methods are used to generate SVD.

The methods are selected depending on the energy of the gas stream, which is characterized by its velocity in the loop and pressure.

The first method consists in abruptly closing the crane on the loop (Fig. 3). In FIG. 3, a loop 1, a crane 2, a gas flow direction 3 are shown. In this case, a high pressure zone is formed at the crane for a short time, which then propagates in the form of an SVD along the loop. An important condition is the short closing time of the crane.

The second method consists in stopping the gas flow on the loop, waiting for the pressure to equalize at the end of the loop to the gas pressure at the wellhead and opening the tap. It is applicable when the loops in the ZPA are combined into a collector, the location of which is perpendicular to the directions of the loops (Fig. 4), and the gas energy for the formation of the SVD by the first method is not enough. In FIG. 4 shows a loop 4 with a nominal diameter of 1000 and a loop 5 with a nominal diameter of 400.

The third method involves the use of a low pressure receiver (RND) (Fig. 5). The gas flow on the loop is stopped, the gas is discharged to the RND, then the gas outlet valve is closed at the RND. The pressure in the RND should be lower than the pressure in the loop by an amount that ensures the formation of the SVD by stopping the gas flow from the loop to the receiver. In FIG. 5 shows a loop 6, a gas flow stop valve 7, a gas outlet valve 8 in the low pressure valve 9.

For the fourth version of the generation of SVD is used RVD. Gas in the WFD is injected by the compressor. The gas flow in the loop is stopped, the gas from the RVD is released into the loop. The receiver 9 in FIG. 5 is used as a WFD.

The latter option for generating SVD also involves the use of RVD. It is completely analogous to the fourth method, except that the WFD is filled with gas from the gas outlet line of the booster compressor station.

The frequency of measurements may vary depending on several factors:

- from thermobaric conditions in the loop, depending on the degree of their proximity to hydrate formation conditions;

- from the dynamics of the growth process of the amplitude of the reflected signal at characteristic points;

- from the speed of the flow.

As a rule, the frequency of scans is 0.5 ... 1.5 hours.

To carry out measurements according to the described method, a high-frequency pressure sensor is used (for example, the PX409 family of sensors [HIGH ACCURACY PRESSURE TRANSDUCERS [Electronic resource]. Access mode: http://www.omega.com/pressure/pdf/PX409_SERIES.pdf) . In FIG. Figure 6 shows an example of an echogram obtained at the initial stage of operation after cleaning the inner surface of the loop by generating an SVD by stopping the flow. As a reference section, a section of a length of 24 meters was taken between the crane and the first loop rotation from the ZPA. On the echogram, the reference section corresponds to the time between the moment the wave is triggered and the first burst. In accordance with the loop passport, the echogram bursts are tied to the structural features of the loop with designation as characteristic points from the set of names N ₁ ... N _m . In FIG. 7 shows an echogram with highlighted characteristic points N ₁ ... N ₆ . In FIG. Figure 8 shows a diagram of a part of a loop with associated characteristic points N ₁ ... N ₅ (for example, they can be U-shaped temperature compensators of a PC). Point N ₆ is outside the shown area and is not indicated in order to maintain clarity.

The length of the reference section and the time interval on the echogram determine the speed of sound in the gas under specific thermobaric conditions. By the formula (3) calculate the temperature in the characteristic areas.

In FIG. Figure 9 shows an example of an echogram for a loop with a gas temperature lower than the gas temperature when scanning a model echogram. The vertical lines indicate the shift of the peak of the characteristic point N ₄ in comparison with the location on the model echogram.

In FIG. 10 shows an echogram, which shows the increase in amplitude and the shift of the burst of the reflected signal corresponding to the characteristic point N ₄ in comparison with the standard echogram. The shift is due to a decrease in the gas temperature in the loop, and the increase in the amplitude of the reflected signal is due to the beginning of the formation of a new local resistance in the vicinity of this characteristic point.

In FIG. Figure 11 shows an echogram, which shows the appearance of a new burst of the reflected signal between bursts corresponding to characteristic points N ₅ and N ₆ which is a sign of the beginning of the formation of a new local resistance between these characteristic points.

The technical result - determining the place of formation of hydrate plugs and reducing the cost of installing the system - is achieved as follows.

The place of formation of the plug is determined using pressure waves. This method allows you to cover a large controlled loop length compared to the prototype, regardless of the presence of bends in the pipeline, because pressure waves attenuate less electromagnetic waves when overcoming sections of pipelines with bends at right angles. At the same time, the accuracy of determining the location of hydrate formation remains sufficient for technological purposes (maximum error ± 10 m). Thus, the method can be used on loops of any type of profiles and lengths, including in the Far North.

The proposed method allows predicting the formation of ice and hydrates based on current thermobaric conditions, moreover, these conditions are refined in each scanning session. Since the thermobaric conditions for the formation of ice and hydrates are different, the proposed method is selective and provides the ability to accurately predict the nature of the potential formation. Thus, the proposed method, in contrast to the prototype, diagnoses the nature of the local resistance that has arisen by direct signs (thermobaric conditions), and not by indirect ones (dielectric constant).

The cost of installing equipment is reduced due to the exception:

- the stage of factory preparation of the pipeline section;

- delivery of bulky cargo to the place of installation;

- large-scale capital work related to installation on a train.

The pressure and temperature sensors necessary for the operation of the system are installed in regular places of installation of instrumentation in a loop, which are prepared without the use of heavy lifting equipment.

When installing a monitoring system, the need to stop gas production for a significant period of time is eliminated. Due to this, they reduce the economic losses associated with underloading of equipment at the gas treatment plant.

Thus, the proposed method allows monitoring and predicting hydrate formation without significant additional costs for installing the system. The present invention can be used in the oil and gas industry, where it is necessary to determine the places of deposition of various substances inside the plume during the gas production process.

Claims (7)

1. A method for monitoring hydrate formation processes in fishing plumes, which consists in periodically generating a scanning wave at the end of the plume, fixing and analyzing the reflected signal, characterized in that they clean the inner surface of the plume being examined, obtain an exemplary echogram for it and determine the characteristic points corresponding to local the resistance of the pipeline, forming the response signal, distinguish characteristic sections between adjacent characteristic points, one of which is taken as a reference, in the process of monitoring periodically create a scanning pressure wave, receive response signals in the form of echograms, determine the propagation speed of the scanning wave from the time the scanning wave travels the reference section, by comparing the received echograms with the reference one reveals the anomalous changes in the response signal in amplitude, if they are connected, they are tied to the pipeline circuit and type of local resistance, analyze the dynamics of the change in amplitude at the obtained characteristic points of the pipeline and conclude that the formation ovogo local resistance to change the travel time of the scanning wave characteristic sections and the gas temperature at the end of the loop is calculated absolute gas temperature T _n in the new vicinity of the local resistance portion n of the recursion formula

where T _n-1 is the absolute temperature in the characteristic region n-1 preceding the region n, ΔL _n and ΔL _n-1 are the lengths of the characteristic regions n and n-1, respectively, Δt _n and Δt _n-1 are the travel times of the scanning wave characteristic sections n and n-1, respectively, constantly measure the gas pressure on the plume sections in the building of the switching armature and the wellhead and calculate the pressure in the vicinity of the new local resistance by their ratio and determine the possibility of existence of crystalline hydrates under given thermobaric conditions in the vicinity of a new local resistance. 2. The method according to p. 1, characterized in that the scanning pressure wave is generated by closing the crane on the cable in the building of the switching armature. 3. The method according to p. 1, characterized in that to create a scanning pressure wave, the gas flow is stopped until the pressure in front of the tap on the ZPA is equalized to the wellhead pressure and the tap is opened. 4. The method according to p. 1, characterized in that to create a scanning pressure wave, use a low pressure receiver, stop the gas flow on the loop, release gas into the receiver, close the tap. 5. The method according to p. 1, characterized in that to create a scanning pressure wave, a high pressure receiver is used, into which the gas is preliminarily pumped by a compressor to a pressure higher than the gas pressure in the loop, the gas flow on the loop is stopped, gas is released from the receiver into plume. 6. The method according to p. 5, characterized in that the high-pressure receiver is filled with gas from the discharge line at the outlet of the booster compressor station. 7. The method according to any one of paragraphs. 1-6, characterized in that the scanning pressure wave is generated with a constant frequency in the range of 0.5 ... 1.5 hours depending on the gas temperature in the loop and the dynamics of the amplitude of the response signal at characteristic points of the echogram.

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