Wells that are the part of one well cluster or different gas and gas condensate well clusters, usually differ by their wellhead gas pressure.
Traditional connection of such wells to a single pipeline causes low pressure wells gas and gas condensate production drop to minimal. As soon as wellhead pressure in low pressure wells become equal to the pressure in the gathering main, gas extraction from low-pressure wells will cease.
At the same time the gas flow from high pressure wells is simply choked to the pressure level in the gathering main by the flow orifice installed on the wellhead.
Jet pumps that use the energy of gas from high-pressure wells to compress the gas from low-pressure wells can be used to increase the gas extraction from low-pressure wells. In this case the jet pump is acting as a compressor. If one jet pump is used, gas from high pressure wells goes to high-pressure nozzle of the jet pump, and gas from low-pressure wells is directed to low-pressure nozzle of jet pump.
GILBERTON INTERNATIONAL INC smart manifold centers use several jet pumps simultaneously, providing the highest possible level of gas extraction from the low pressure wells.
The direct application of jet pump systems is impossible at the gas condensate wells, since condensate and water contained in the gas prevent effective acceleration of gas in the jet pump nozzles, which leads to low efficiency of ejection. In such cases GILBERTON INTERNATIONAL INC uses jet pumps in combination with in-line separators. In-line separators are axial cyclones where all gas-dynamic elements are mounted inside the pipeline elements. Gas-liquid flow separation in such separators is achieved by separation of gas stream droplets by centrifugal forces generated by swirling gas flow. Inline separators are installed in the smart manifold center to separate liquid from the gas streams directed to jet pumps. Lack of fluid in jet pumps helps to maximize the effective use of energy to compress the low-pressure gas. With high level of content of liquid fraction in low-pressure gases it is also possible to use in-line separators in smart manifold centers. Configuration of each smart manifold center is chosen individually, depending on specific pressure profile in connected wells, gas discharges and compositions.
GILBERTON INTERNATIONAL INC produces smart manifold centers designed to connect gas and gas condensate wells in well clusters and gas treatment plants.
The figure shows a schematic diagram of one of the possible designs of smart manifold center for four wells. Two of the wells (1St and 4th) have gas overpressure. This is the case when the block is used on the gas-condensate field. Two in-line separators C-1 and C-2, which separate liquid from the gas coming to high-pressure nozzle jet pumps, are installed to provide normal operation of jet pump. Hydrocarbon liquid and water, separated in separators C-1 and C-2, are fed into the mixture at the jet pumps’ outlet.
In the graph the dependence of compression ratio e from ejection coefficient k of jet pumps, which are part of entry manifold units, is shown for different levels of gas pressure loss in the low and high pressure wells.
Smart manifold centers are supplied with orifice flow meters which determine flow consumption rates of all connected wells. It is also mandatory to install pressure gauges (or pressure sensors) into the blocks in order to determine the pressure in all pipes connected to the unit.
If required, the jet pumps can also be supplied with control units which provide automatic adjustment of jet pumps’ internal gas-dynamic elements for the maximum gas production from the low-pressure wells. All assembling parts of the units are produced in Russia. The figure shows an overview of smart manifold center designed for one of the customers of GILBERTON INTERNATIONAL INC.
In practice the production is not always predictable. Well conditions change over time and facilities need to be able to adjust block parameters to adapt to changes.
Jet pumps are fixed-design devices. Each of our jet pumps is custom-designed to function at specific operating conditions described by Customer. That’s why we have invented Universal Design Jet pump with replaceable internal components.
The Universal Design is comprised of an outer casing, which is basically a pipe section, and two replaceable components inside, responsible for the Jet pump’s operating characteristics. These two components are called the nozzle and the diffuser and in the Universal Design they can be easily replaced with different configurations determined by required operating parameters.
Since operation conditions change overtime, injector inner block can also be replaced by newer, more suitable for changed conditions. By replacing the internal blocks at recommended intervals, high operating performance can be maintained over the lifetime of the unit, maximizing gas recovery from the low-pressure wells.
Universal Design nozzle and diffuser sections are explicitly designed to allow the Jet pump to operate under new production conditions.
Smart manifold center is the most effective solution for generating extra production from low- pressure wells to extend field life. Often shut-in or drowned wells can be restarted, as well as satellite or stranded wells previously deemed too expensive to recover with ‘traditional’ techniques.
With the help of smart manifold center, gas from the high-pressure well can be used to provide the efficient operation of the built-in jet pump unit, which not only brings the high-pressure gas pressure to a suitable level to meet downstream conditions, but also lowers the pressure of the nearby low-pressure wells, bringing them back to life.
Particularly high economic results can be reached using smart manifold centers in the well clusters, where the pressure of low-pressure wells is comparable to or even lower than the pressure in the gas main. For example, if the pressure in the high pressure gas well is 150 atm, and the gas flow is 30 OOO Nm3/h, with gas pressure in the gas main equal to 75 atm, we can compress about 45 OOO Nm3/h of low-pressure gas under the pressure of 65 atm after installation of GILBERTON INTERNATIONAL INC blocks.
Thus, for the given case the use of smart manifold centers gives 2.5-fold increase of gas production for example wells.
The diagram shows the P-Q curve for a typical low-pressure well.
Yellow line represents the operating conditions before the fitting of a smart manifold center. With use of energy from a suitable high pressure source (i.e. throttled high-pressure well) jet pumps,
fitted into manifold block, can be used to lower the head pressure of the low-pressure well.
If the pressure reduction achieved by the Jet pump at the well head is ‘AP’ on the diagram, then the increased production from the low-pressure well will be represented by ‘AQ’.
In the case of nearly and fully shut-in wells, the increase in production rates can be significant, since the P-Q curve is at its flattest in this region (a small drop in pressure causes large increase in production). In many cases ‘dead’ or shut-in wells can be restarted by lowering the pressure at well head.
Jet pump design
Gas jet pump is a device where excess pressure of high -pressure gases is used for low – pressure gas compression.
Low-pressure gas ejecting process can be described as follows: high-pressure gas flow is passing under high pressure and at high velocity through the supersonic nozzle, creating a low pressure area in the mixing chamber of jet pump. Since the pressure in this area is lower than the pressure of low-pressure gas, low-pressure gas flows into the mixing chamber of jet pump. Low-pressure gas suction depends on the degree of rarefaction in the mixing chamber. In the mixing chamber of the jet pump the high-pressure flow mixes with the low-pressure flow, forming the mixed flow. From the mixing chamber, the mixed flow enters the diffuser where it is decelerated and gas static pressure is increased. The pressure of the mixed flow at the outlet of jet pump exceeds the pressure of low-pressure gas.
Thus, the pressure of low-pressure gas increases without the mechanical energy consumption. Thus, the use of jet pump technology in the oil and gas industry provides more robust and reliable technical solution compared to mechanical blowers (compressors, gas blowers, fans, etc.).
GILBERTON INTERNATIONAL INC company created an jet pump system with unique characteristics for sustainable gas compression in close cooperation with specialists of Central hydrodynamic Institute (TsAGI).
To determine the safe operating range of jet pump systems, methods of calculation for real gases flows are used, which were previously developed for flow analysis in spacecraft industry. These methods provide a reliable calculation for safe operating range of jet pump exploitation and their critical modes. As an example, figure below shows the distribution of flow velocity in the channel of a supersonic jet pump.
These jet pump systems can be easily integrated into the standard manifolds of inlet wells.
In-line separator is a device for separating continuous gas-liquid flow into gas flow and liquid flow.
Gas-liquid mixture is twisted in the tangential swirler, which is installed at the device inlet, and further directed into the cylindrical channel where the liquid is separated at the pipe walls. Liquid film is formed on the walls of cylindrical channel and the gas stream is formed in the near-axial zone. At the outlet of cylindrical channel there is a separating section, where the flow is divided into gas stream and liquid stream. All elements of separator are mounted within the pipeline.