Patent Application
20150316257
Hydrocarbons are widely used as a primary source of energy, and have a significant impact on the world economy. Consequently, the discovery and efficient production of hydrocarbon resources is increasingly important. As relatively accessible hydrocarbon deposits are depleted, hydrocarbon prospecting and production has expanded to new regions that may be more difficult to reach and/or may pose new technological challenges. During typical operations, a borehole is drilled into the earth, whether on land or below the sea, to reach a reservoir containing hydrocarbons. Such hydrocarbons are typically in the form of oil, gas, or mixtures thereof which may then be brought to the surface through the borehole.
Well testing is often performed to help evaluate the possible production value of a reservoir. During well testing, a test well is drilled to produce a test flow of fluid from the reservoir. During the test flow, key parameters such as fluid pressure and fluid flow rate are monitored over a time period. The response of those parameters may be determined during various types of well tests, such as pressure drawdown, interference, reservoir limit tests, and other tests generally known by those skilled in the art. The data collected during well testing may be used to assess the economic viability of the reservoir. The costs associated with performing the testing operations are significant, however, and may exceed the cost of drilling the test well. Accordingly, testing operations should be performed as efficiently and economically as possible.
One common procedure during well testing operations is combusting the waste gas flow associated with the well effluent. Various types of flare systems may be used to burn the waste gas flow. For example, flares having Coanda surfaces have been widely used in the petroleum industry to flare waste gases generated at oil refineries and production platforms. A Coanda surface is merely a curved surface designed for the adherence of a fluid. Fluid streams injected on or adjacent to a Coanda surface tend to adhere to and follow the path of the surface. The negative pressure pulls the fluid against the surface. The fluid stream is spread into a relatively thin film or sheet, which allows proximate fluids to be mixed in with the fluid stream in a very efficient manner. The additional surface area imparted to the gas significantly enhances mixing. In a flare, for example, which may emit tens of thousands of pounds of waste gas per hour, fast mixing is desirable. As a result, Coanda surfaces and the Coanda effect are commonly used in flare apparatus as it eliminates the need for steam, blowers and related equipment.
Accordingly, Coanda flares provide relatively clean combustion by premixing the waste gas with ambient air prior to combustion. Coanda flares also offer generally good, stable flame combustion at high inlet pressures of the combustible gas. In addition, flow velocity perturbations in shockwaves generated in the general vicinity of the gas exit slot of a Coanda flare may atomize liquid droplets entrained in the gas flow, thereby generated a fine mist that facilitates combustion and reduces the risk of fall out even where there is significant liquid carryover in the flare line. Accordingly, Coanda-type flare systems offer stable and clean combustion of multiphase hydrocarbon effluents, and may be operated in an efficient and environmentally friendly manner.
In some well test operations, well test separators may be used to separate the well effluent into its individual phases, such as oil, water, and gas. This approach requires additional separating equipment and increases the footprint needed for the well test system, which may be a significant concern in certain applications, such as on offshore platforms.
Additionally, some drawbacks to the use of Coanda-type flare systems to burn waste effluent during well testing include noise, ejected debris, and sensitivity to flow rate variations. The noise is believed to be mainly associated with shockwaves and is generally excessive and poses safety and environmental issues. Furthermore, there is a high risk of debris being ejected radially from the Coanda slot. Such debris may pose a serious risk of injury to nearby operators as well as damage to surrounding equipment. Still further, a fraction of larger droplets may not follow the gas flow path and instead may spray sideways from the slot, causing fallout, especially if the liquid in the effluent flow is highly viscous.
Moreover, during well testing operations there may occur frequent and unexpected flow rate variations, as well as variations in the composition of the hydrocarbon effluent (e.g., the liquid fraction in the gas stream), that may lead to a periodic breakdown of the Coanda effect (i.e., the flow path of the gas or liquid droplets may divert from the Coanda profile). During these periodic breakdowns, the gas/liquid mix may spray radially outwardly, causing unintended side effects and dangers.
Still further, the use of Coanda-shaped burners may generate a supersonic jet of fluid that creates shockwaves close to a surface of the burner. As known in the field of Aerodynamics, Prandl-Glauert condensation clouds may develop behind an air vehicle traveling at near-sonic velocities through a high-humidity atmosphere. Shockwaves generated near the vehicle may create a local zone of high pressure that precedes the shockwave and a local zone of low pressure that follows the shockwave. Before ambient air can fill the low pressure zone, the temperature of the gas present in the low pressure zone will decrease sharply to a very low temperature (down to 150K). When the temperature drop trailing the shockwave is severe, the condensed water droplets may be converted into ice and stick to the tulip-shaped body. This effect may be applied to Coanda flare systems, where a significant pressure drop at the exit of a nozzle may freeze the liquid component of the waste flow, thereby halting or decreasing the efficiency of the waste gas combustion.
In accordance with certain aspects of the disclosure, a flare is provided for combusting waste effluent from a reservoir. The waste effluent flare may include a supply pipe configured to fluidly communicate with the reservoir so that a flow of waste effluent travels through the supply pipe, and may include a supply pipe inner surface and a supply pipe discharge end. The flare may further include a flare body extending along a flare body axis. The flare body may have a stem disposed within the supply pipe and extending substantially coaxially along the flare body axis, and a stem outer surface spaced from the supply pipe inner surface to define an annular gap therebetween. The flare body may also include a head having a streamlined shaped exterior surface. A transition section of the head may be coupled to the stem and include an annular bulge extending circumferentially around and projecting outwardly from an exterior surface of the transition section. The bulge may be substantially axially aligned with the annular gap. In some embodiments, the flare body head may include an initial portion substantially axially aligned with the gap and extending at a deflection angle relative to the flare body axis, wherein the deflection angle is approximately 40 to 70 degrees. In other embodiments, an atomization tube may be coupled to the flare body stem and have an inlet end fluidly communicating with the supply pipe and an outlet end disposed in a body chamber defined by the flare body, wherein the outlet end defines a discharge orifice.
The summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.
Embodiments of the flare for multiphase effluent flow are described with reference to the following figures. The same numbers are used throughout the figures to reference like features and components.
It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.
So that the above features and advantages of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only typical embodiments of this disclosure and therefore are not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
The terms “Coanda” and “Coanda-shaped” are generally understood by those of skill in the art to define a flare body geometry that facilitates a jet of fluid that closely adheres to the flare body surface. The Coanda surface may alternatively be referred to as having a tulip shape, because the smooth, concentric geometry emulates the shape of that flower. Regardless, this type of phenomenon, like in the presently disclosed embodiments, may be present or can be achieved without having the typical Coanda or tulip shape.
The waste effluent flare is used to burn, or combust, waste effluent from a supply flowline. The generic term used to describe such waste effluent is often roughly termed a gas flow to be combusted. The gas flow, however, is often a multiphase flow, in which a fraction of liquid remains in the gas flow to be combusted. A Coanda-type flare is often useful to combust the liquid fraction, since the gas flow ejected from the Coanda flare reaches supersonic speeds. The flow velocity perturbations in shockwaves created by these speeds disperse the liquid fraction in the gas flow into a fine mist that is more easily combusted by the burner flame. The waste effluent (which may be a single-phase or dual-phase fluid) flows closely to the surface of the flare and may entrain primary air.
As shown in
The waste effluent flare 100 may also include a flare body 120 extending along a flare body axis 122. The flare body 120 may include a stem 124 disposed within the supply pipe 102 and extending substantially coaxially along the flare body axis 122. The stem 124 may have a stem outer surface 126 spaced from the supply pipe inner surface 104 to define an annular gap 128 therebetween through which waste effluent may flow.
The flare body 120 may also include a head 130 having an exterior surface 132 which promotes a waste effluent flow that closely follows the exterior surface 132. The head 130 includes a transition section 134 coupled to the stem 124, a middle section 136 flaring outwardly from the transition section 134, and a distal section 138 defining a head discharge end 140. The exterior surface 132 generally has axial symmetry with a variable curvature along the flare body axis 122. In the middle and distal sections 136, 138, the exterior surface 132 is substantially smooth with gradual changes in diameter to promote an effluent flow pattern 135 that closely follows the shape of the exterior surface 132. The flow pattern 135 generates high velocity flows with resulting low pressures which draw ambient air 137 into the effluent, thereby mixing air with the effluent flow.
The transition section 134 may include an annular bulge 142 for dispersing liquid phase effluent into the effluent flow pattern 135. In the embodiment illustrated in
The flare body 120 may be configured to more reliably generate the flow pattern 135 with the streamlined shape and to reduce the incidence of solids projecting radially outwardly from the flare body 120. More specifically, the initial portion of the flare body 120 that extends outwardly from the stem 124 may be oriented at a relatively small deflection angle “α” relative to the flare body axis 122. In the embodiment of
The waste effluent flare 100 may also be configured to alleviate rapid cooling associated with the low pressure area of effluent flow. In the illustrated embodiment, the bulge 142 may produce a high velocity waste flow immediately downstream of the bulge 142. The increased velocity flow also creates an area of low pressure and a resulting drop in temperature that tends to freeze liquid fluid immediately downstream of the bulge 142. To address the surface icing issue, the flare body 120 may include a body interior surface 150 defining a body chamber 152. The transition section 134 of the flare body 120 may include a plurality of apertures 154, wherein each aperture 154 extends from the body interior surface 150 to an exterior surface 132 of the flare body 120. In the illustrated embodiment, the apertures 154 form two concentric bands 156, 158 extending circumferentially around the flare body 120, however the apertures 154 may be provided in other patterns and more bands. Each aperture may have a diameter of approximately 2 to 5 millimeters. The apertures 154 direct warmer air from the body chamber 152 toward the area of low pressure immediately downstream of the bulge 142, thereby to prevent surface icing. The size and number of apertures 154 may be selected such that they permit a sufficient amount of warm air flow to the exterior surface 132 while preventing a reverse flow of fluid into the body chamber 152.
The waste effluent flare 100 may include additional features for breaking up and/or atomizing liquids entrained in the waste effluent. For example, a plurality of supply pipe projections 190 may be formed at the supply pipe discharge end 106. Additionally or alternatively, a plurality of head projections 192 may extend from the head discharge end 140. The supply pipe projections 190 and head projections 192 may be formed as series of tabs that are shaped, such as triangular, to form discrete, spaced points. The tabs may have a height (measured substantially parallel to the flare body axis 122) of approximately 1.5 to 6.0 millimeters. These points may help disperse liquid content of the waste effluent for improved mixing and subsequent combustion. For example, the supply pipe projections 190 may help disperse liquid that may travel along the supply pipe inner surface 104 into droplets or discrete streams that may more easily mix with the downstream effluent gas flow around the head 130. Similarly, the head projections 192 disperse liquid traveling along the exterior surface 132 for mixing with effluent gas and ambient air downstream of the head 130. The head projections 192 also increase the turbulence of the gas flow to improve mixing and reduce noise.
The exterior surface 132 of the flare body head 130 may also be configured to promote dispersion of liquid entrained in the waste effluent. As shown in
During operation, waste effluent flows through the supply pipe 102 and is discharged through the annular gap 128 toward the flare body head 130. The gap 128 directs the waste effluent toward the bulge 142 which may define a reduced deflection angle α. The gas portion of the waste effluent may be traveling at sonic speeds, which disperses any liquid portion of the waste effluent into a fine mist. The effluent flow then traverses the flow pattern 135 around the flare body head 130, staying near the exterior surface 132 due to the Coanda effect.
The waste effluent flare 200 may be operated in two different modes to accommodate different waste effluent flow rates. During low and moderate effluent flow rates, the flare 200 may be operated in a first mode in which the waste effluent may be directed entirely to the atomization tube 262 so that no effluent passes between through the gap 238 between the stem 224 and supply pipe 202 to an exterior surface 232 of the flare body 220. The first mode may be used when subsonic or sonic flow speeds are achieved inside the atomization tube 262. At high effluent flow rates, the flare 200 may be operated in a second mode in which the waste effluent may be directed to the gap 238. By providing multiple modes of operation, the waste effluent flare 200 may obtain efficient combustion over a wider range of effluent flow rates.
While the foregoing illustrative embodiments have been described in connection with an effluent flow having two or three phases, it will be appreciated that the flares may also be used with waste effluent having a low or zero liquid content and therefore may be operated as “dry gas” flares.
Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the flare for multiphase effluent flow disclosed and claimed herein. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/RU2012/001028 | 12/6/2012 | WO | 00 |
