Patent Application
20180023350
This application claims priority to Russian Application No. 2016129941 filed Jul. 21, 2016, which is incorporated herein by reference in its entirety.
The disclosure relates to methods for preventing formation of slugs of fluid blocking a pipe cross-section when transporting a gas-liquid mixture in wellbores and pipelines during production of hydrocarbons in the oil and gas industry.
In cases where a wellbore or a pipeline is not straight and in addition to the horizontal sections it contains ascending, descending and vertical segments, the so-called slug flow regime can be established. In this regime, intermittent single-phase portions of gas and liquid (slugs) are transported in the pipe. The high-speed slug flow regime is dangerous for surface equipment. It also leads to pressure oscillations at the bottom-hole of a wellbore, which in turn can lead to undesirable geomechanical effects, such as damage to a near-wellbore part of a stratum and deterioration of its conductivity, extensive solid-phase migration to the wellbore, and proppant backflow, especially in case of stimulation by a multistage hydraulic fracturing of the stratum. In the horizontal part of the pipe, the stratified flow regime is usually established, in which gas moves over a layer of heavier liquid (oil or oil with mixture of water). When the pipeline deviates from the horizontal level, a pipe lumen in the knees can be blocked periodically by the liquid accumulated in lower regions of the pipeline. In the case where the horizontal section becomes vertical, a fluid slug is also developed. When the mixture enters the vertical section, rapid segregation takes place, in which the liquid blocks the entrance to the vertical section, thus preventing the free passage of incoming gas. As a result of development of a fluid slug blocking the pipeline, the gas is accumulated behind it, in which the pressure rises with time. In the course of time, the pressure of the accumulated gas becomes sufficient to push through a portion of the accumulated fluid, thus establishing the non-stationary flow regime with periodic splashes of large portions of the liquid phase.
Various methods for controlling slugging in a gas-liquid mixture flow are known from the prior art. Thus, U.S. Pat. No. 6,041,803 A describes a device and a method for preventing formation of slug flow regime in an ascending segment in which the inlet stratified flow is converted into a non-stratified regime (annular or bubble). The apparatus includes a convergent nozzle and a divergent diffuser.
Application US 20090301729 A1 discloses a device for controlling the slugging in a multi-phase flow, being a pipe having a specific structure of sections of 1 to 30 feet long, inclined at an angle of 5-90 degrees to the horizon.
U.S. Pat. No. 6,716,268 B2 relates to control of development of slugs in a riser by controlling gas pressure at the bottom of the riser. For this purpose, a separation tank is used, which includes a valve to control gas velocity in a pipeline. If the monitored pressure exceeds some empirically determined value, the valve opens and changes the gas velocity, which prevents the appearance of plugs.
The article “Experimental investigation of terrain slugging development, evolution and potential for mitigation” of Brasjen, B. J., et. al., 16th International Conference on Multiphase Production Technology, The BHR Group, 2013, describes a set of devices to be mounted in circumhorizontal inclined pipes for dissipation of fluid plugs. In the experiments, the authors observed the decrease in pressure fluctuation up to 16%.
The known methods and devices are mainly intended to be used only at the entrances to risers and do not allow ensuring the reliable prevention of slug flow regime formation, since they consider neither the expected flow rate of the gas-liquid mixture nor the geometry of the pipeline.
The disclosure ensures reliable prevention of slugs development during a gas-liquid mixture flowing in non-linear wellbores and pipelines due to consideration of an expected flow rate of the gas-liquid mixture and a geometry of a wellbore or a pipeline when choosing the mounting location of the device for preventing slugs.
The disclosed 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 a wellbore or a pipeline by mathematical simulation based on expected values of the gas-liquid mixture flow and the 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.
Different types of devices, for example, vortex-type devices, twisted-tube bundle devices, mixer-type devices, rotating brush type devices, can be used to convert the stratified gas-liquid mixture flow into the dispersed flow.
The disclosure is explained by the drawings, where
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.
The geometric configuration of a wellbore such as that shown in
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.
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.
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 (
The device shown schematically in
The device of
The method can be implemented as follows.
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).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016129941 | Jul 2016 | RU | national |
