METHOD FOR PREVENTING FORMATION OF A SLUG FLOW REGIME OF A GAS-LIQUID MIXTURE IN A NON-LINEAR WELLBORE OR PIPELINE

Abstract

A method for preventing formation of a slug flow regime of a gas-liquid mixture in a non-linear wellbore or a pipeline comprises determining at least one most probable place of fluid slugs development in the wellbore or the pipeline by mathematical simulation based on expected values of the gas-liquid mixture flow and known geometry of the wellbore or the pipeline and mounting a device, in the determined place of fluid slug development, that converts the stratified gas-liquid mixture flow into a dispersed flow.

Claims

1. A method for preventing formation of a slug flow regime of a gas-liquid mixture in a non-linear wellbore or pipeline, the method comprising: determining at least one most probable place of fluid slugs formation in the non-linear wellbore or pipeline by mathematical simulation based on expected values of the gas-liquid mixture flow and known geometry of the wellbore or the pipeline, and mounting a device, in the determined place of fluid slug development, that converts a stratified gas-liquid mixture flow into a dispersed flow.

2. The method of claim 1, wherein a vortex-type device is used as the device that converts the stratified gas-liquid mixture flow into the dispersed flow.

3. The method of claim 1, wherein a twisted-tube bundle device is used as the device that converts the stratified gas-liquid mixture flow into the dispersed flow.

4. The method of claim 1, wherein a mixer-type device is used as the device that converts the stratified gas-liquid mixture flow into the dispersed flow.

5. The method of claim 1, wherein a rotating brush type device is used as the device that converts the stratified gas-liquid mixture flow into the dispersed flow.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0012] The disclosure is explained by the drawings, where FIG. 1 shows a diagram of a gas-liquid mixture flow with a fluid slug developed in a wellbore having inclined and vertical sections;

[0013] FIG. 2 shows a diagram of the gas-liquid mixture flow in the same wellbore with the devices mounted therein, that provide conversion of the stratified flow into the dispersed bubble flow;

[0014] FIG. 3 shows an example of a device for conversion of the slug flow regime into a dispersed one, configured as a bundle of tubes,

[0015] FIG. 4 shows an example of a device for conversion of the slug flow regime into the dispersed one, configured as a rotating brush;

[0016] FIG. 5 shows an example of a pipeline geometry,

[0017] FIG. 6 shows a slope of the pipeline of FIG. 5, depending on the coordinate of the pipe,

[0018] FIG. 7 shows distribution of oil volume fraction across the pipeline at the moment of appearance of fluid slugs, obtained as a result of mathematical simulation.

DETAILED DESCRIPTION

[0019] The disclosed method is aimed at preventing formation of a slug flow regime in inclined and vertical sections of a wellbore or a pipeline, in those places where such regime is most probable upon results of mathematical simulation of the gas-liquid flow in a wellbore or a pipeline. In mathematical simulation, a geometry of the wellbore or the pipeline is used as obtained, for example, from a drilling log for the case of a wellbore, or directly measured where possible. For the expected flow rates, the flow regimes of the gas-liquid mixture in the wellbore or the pipeline containing, in addition to the horizontal section, inclined and vertical parts, are determined based on the numerical simulation, and at least one most probable place of development of fluid slugs is detected. Devices that convert the stratified flow of the gas-liquid mixture into the dispersed bubble flow are mounted in the determined most probable places of development of fluid slugs, which significantly increases the segregation time and significantly reduces the period between the fluid slugs and thus alleviates negative consequences of the slug flow regime.

[0020] The geometric configuration of a wellbore such as that shown in FIG. 1 leads to the formation of a slug flow regime in vertical and inclined sections due to gravitational segregation of the gas-liquid flow. A gas-liquid mixture enters a wellbore 1 from the side 2 and exits from the side 3. Here, a liquid phase 4 can move as a layer under a gas phase 5 and develop slugs in the zones 6a and 6b due to the influence of gravity and deviations of the pipeline from the horizontal position. At bottom points of the inclined sections, heavy fluid accumulates and blocks the lumen of the pipe 6a, then the gas-liquid flow from the circumhorizontal section enters the vertical part where, due to the gravity action, rapid segregation occurs and a heavy liquid blocks a lumen of the pipe, thereby preventing free passage of the gas. As a result, pressure in the blocked gas volume rises and the fluid slug is pushed upward. Such splashes produce high-frequency pressure oscillations, which in turn can lead to undesirable geomechanical damage to the near-wellbore area, reduction in conductivity of the crack and reduction in hydrocarbon production from the stratum.

[0021] The risk of geomechanical damage to the near-wellbore area directly depends on the rate of change in pressure, i.e. from the derivative of the pressure over time (the higher its value, the higher the risk of damage). Thus, the decrease in frequency of pressure oscillations helps to reduce the risk of damage to the stratum.

[0022] To prevent high-frequency pressure oscillations, it is proposed to increase segregation time as far as possible in the regions where slugs are most likely to appear. For this purpose, it is proposed to convert the stratified flow into the dispersed flow by means of special devices. The stratified flow, passing through such devices, will be converted into a bubble or gas-droplet flow (depending on the volume fractions of the phases). For a dispersed flow, the segregation time is significantly higher, which will either completely prevent the development of fluid slugs or significantly reduce the rate of their development. FIG. 2 shows a diagram of gas-liquid mixture flow in a wellbore having inclined and vertical sections where the stratified flow 8 is converted by means of a special device 7a into the dispersed bubble flow 9, which in turn can be segregated into the stratified one and then re-converted into the dispersed flow 10 by means of the device 7b.

[0023] To convert the stratified flow into the dispersed one, the devices of various types can be used, for example, of the vortex type (http://www.chengfluid.com/), in the form of a twisted-tube bundle (FIG. 3), various variants of mixers (http://Www.stamixco-usa.com/plug-flow-reactors), in the form of a rotating brush (FIG. 4), etc.

[0024] The device shown schematically in FIG. 3, is a bundle of twisted tubes (not less than 2). Being mounted in the stratified gas-liquid flow, this device redirects the gas phase from the upper part of the flow to the lower one, and the liquid phasein the opposite way, which leads to phase mixing and formation of a dispersed mixture. The length of such device shall exceed the diameter of the pipeline. The device can be made of various materials, for example, plastic or metal.

[0025] The device of FIG. 4 is a rotating brush for mixing the stratified gas and liquid phases. For effective mixing, the length of such device shall exceed the diameter of the pipeline. The device can be made of various materials, for example, plastic or metal. The exact position of the device is determined on the basis of mathematical numerical simulation of the gas-liquid flow in a pipeline of a given configuration.

[0026] The method can be implemented as follows.

[0027] Based on the well-known pipeline geometry derived from direct measurements or basing on drilling log data and typical flow rate of the phases, one can determine the possibility of establishment of the slug flow regime, as well as the exact place of the slug development, for which purpose, mathematical numerical simulation is used. Simulation can be based on solving non-steady-state equations of a multi-fluid model or a drift model derived from the laws of conservation of mass and pulse of continuum mechanics. The details of these methods and the features of the numerical solution of the determining equations are presented, for example, in the work (Theuveny B. C. et. al. Integrated approach to simulation of near-wellbore and wellbore cleanup//SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers, 2013).

[0028] FIGS. 5-7 show an example of numerical simulation of the oil and gas flow in a pipeline. FIG. 5 is a general view of the pipeline geometry, FIG. 6 shows the slope of the pipeline depending on the coordinate of the pipe defining the side-view in FIG. 5a. Numerical simulation was carried out for constant oil and gas flow rates specified at the pipeline inlet and presented in Table 1. The outlet of the pipeline is considered to be open into a region with constant atmospheric pressure (see Table 1).

TABLE-US-00001 TABLE 1 The gas flow rate at the pipeline inlet, m/s 0.14 The oil flow rate at the pipeline inlet, m/s 0.027 Pipeline outlet pressure, atm. 1.0 Coordinates of slug development points, m S.sub.1 = 150.5 S.sub.2 = 758.9

[0029] FIG. 7 shows distribution of oil volume fraction across the pipeline at the moment of appearance of fluid slugs, obtained as a result of mathematical simulation. The points S.sub.1 and S.sub.2 in FIG. 7 denote the sites where the slugs will appear and before which it is necessary to mount a device for converting the stratified flow into the dispersed one. The calculated exact coordinates of these points are given in Table 1.