Systems and methods for diluting a subsea scale inhibitor to prevent production string failure

Abstract

This invention attempts to address the problem of hydraulic discontinuity by combining two methods. The reduction of fluid density is promoted by diluting the inhibitor product with a water-based fluid and increasing the fluid flow rate. The first method reduces the hydrostatic pressure gradient in the injection line, while the second method increases the pressure drop due to friction in the line. This combined effect prevents hydraulic discontinuity in the injection. To this end, the invention incorporates an industrial water tank, pump, and line fitting (flow rate T) on ground equipment. This assembly is used to dilute the inhibitor in the injection line while ensuring a minimum inhibitory concentration.

Description

Technical Field

[0001] The application field of this invention is oil exploration and production. More specifically, this invention falls within the field of reservoir management, specifically scaling management, lifting, and flow technologies to ensure flow and maintain production. Background Technology

[0002] Scale formation, which is the formation of solid deposits in a water system when changes in the physical or chemical environment of the system cause the solubility limits of certain components to be exceeded, is a problem in many industrial operations involving water fluids, such as in the oil and gas industry, mining, papermaking, and geothermal power generation.

[0003] Particularly in the oil and gas industry, fouling deposits on equipment surfaces can lead to blockages or clogs, resulting in costly production interruptions and safety risks from unexpected pressure build-ups. In oil and gas wells and related equipment (such as wellheads, flow lines, production tubing, or other processing and transport equipment), fouling formation primarily results from instability caused by pressure and temperature variations in formation water, as well as the mixing of incompatible water fluids. For example, when seawater is used as an injection fluid to drive oil through subsea formations toward a production well, the difference in ion content between the injected seawater and the formation's natural water can lead to the precipitation of organic salts.

[0004] Without proper treatment, precipitated salts form deposits that obstruct the flow of oil toward production wells and accumulate on production equipment, eventually causing well blockages. Similarly, precipitated salts can form accumulated deposits on equipment associated with hydrocarbon production, processing, and transportation.

[0005] To avoid such blockages, scale inhibitors are widely used in the oil and gas industry, and the problem of dirt on equipment surfaces can be solved by continuously injecting scale inhibitors into the equipment.

[0006] To prevent fouling within oil / gas transport formations, two techniques are typically used. In one technique, a scale inhibitor may be contained in a fluid (usually water) and injected into the formation through one or more injection wells, for example, to drive oil toward a production well (water drive treatment). In another technique, known as "compression treatment," a fluid containing a scale inhibitor (also usually water) may be introduced into the production well (after production has ended) to "compress" the scale inhibitor into the rock formation surrounding the production well. Thus, the scale inhibitor is supplied to the formation rock to prevent fouling deposits from forming in the formation itself (pore blockage) and subsequently in downstream production units.

[0007] Scale formation can only be controlled when a sufficient amount of scale inhibitor is supplied. In the case of "compression treatment," the scale inhibitor concentration will decrease over time until it needs to be repeated with scale inhibitor ("recompression" treatment). Therefore, it is very useful to analyze the fluid produced from the production well to ensure that the scale inhibitor concentration is always maintained at a level sufficient to inhibit scale formation. By analyzing the level of scale inhibitor in the production fluid, the consumption of scale inhibitor concentration can be monitored, and thus it can be determined whether repeated treatment with scale inhibitor is necessary. Ideally, the scale inhibitor level should be accurately determined as a preventative measure against the risk of scale deposition and the resulting production loss. On the other hand, supplying more scale inhibitor than required is undesirable from the perspective of the cost of excess scale inhibitor and the production interruption required for each new compression treatment.

[0008] In this context, the technical problem that prompted the present invention is the need to increase the flow rate of the scale inhibitor to compensate for possible discontinuities in the hydraulic connection, referred to herein as "string breakdown".

[0009] However, as already mentioned, this increase contributes to unnecessary expenditures on chemical products. The solution achieved by this invention is to dilute the scale inhibitor product to the minimum concentration required to avoid interruption of the liquid column within the tubing, reduce the specific mass of the solution, and maintain the injection concentration above the minimum inhibitory concentration (MIC, minimum injection concentration). Discontinuous hydraulic connections (also known as interruption of the liquid column within the tubing) occur when the hydrostatic pressure gradient in the metering supply line exceeds the pressure drop due to friction.

[0010] Dilution of inhibitor concentration addresses column interruptions in the tubing in two ways. First, dilution aims to reduce the fluid density in the metering line, thereby lowering the hydrostatic gradient and allowing operation over a wider range of column bottom pressures. Second, inhibitor dilution controls product consumption by maintaining the minimum required inhibitor concentration without over-injecting product.

[0011] Therefore, this invention seeks to stabilize the liquid column in a chemical injection line during inhibitor injection operations. This invention is applied in parallel with a chemical injection system to provide volumetric support and prevent liquid column interruption within the column. The diluent used is water, and the principle of this invention is based on maintaining a minimum injection concentration and providing additional flow to prevent liquid column interruption within the column.

[0012] Expected advantages

[0013] The economic advantage relates to savings achieved by avoiding waste of chemical products (scale inhibitors), where increasing the scale inhibitor flow rate is a way to prevent interruption of the liquid column in the tubing during scale inhibitor pumping. Productivity is related to maintaining the pumping of scale inhibitors, thereby avoiding fouling and the resulting production losses associated with blockage of the well's production tubing.

[0014] The health and safety advantages are related to the simplicity of the adaptation operation, which does not require intervention in the well. All changes are made at the platform level, without the need for rig movement or high-risk operations.

[0015] Due to the intermittent nature of product injection, interruptions in the fluid column within the tubing can lead to a loss of control over the volume of inhibitor injected into the well. Intermittent injection can cause disruptions to the inhibition process, which can last from hours to days. The intermittent nature of scale inhibitor injection promotes discontinuity in the fouling inhibition process, resulting in scaling in the well's production tubing, which can potentially clog oil production. Therefore, this invention improves the reliability of the fouling inhibition process by ensuring that well production is not reduced due to the presence of fouling in the production tubing, in addition to increased control over the chemical injection process.

[0016] The continuous and uninterrupted injection of scale inhibitors ensured by this invention prevents scaling, allowing for stable and controlled well production and maintaining a production level that guarantees value for Brazilian society.

[0017] In addition, the increased flow rate resulting from parallel or series connections of pumps is one possible alternative. The increased flow rate promotes increased pressure loss within the pipeline, which is another possible solution to the problem. However, this alternative has technical and economic limitations. To achieve the necessary pressure loss to avoid flow intermittency, excessively high flow rates may be required, which, besides potentially disrupting flow patterns in the production string, also wastes inhibitory products, making it a less economically attractive solution. Summary of the Invention

[0018] The present invention includes a method for diluting scale inhibitors in subsea production equipment to prevent malfunctions in production tubing and systems.

[0019] The original system consists of a main chemical injection pump and a scale inhibitor connected to a chemical injection mandrel on the platform, such as... Figure 1A As shown. In the proposed invention, an auxiliary chemical injection pump is connected in parallel with the main chemical injection pump via a manifold to promote mixing between the two flow lines (filtered industrial water and scale inhibitor) to achieve a flow rate that prevents tubing failure in the vertical section of the injection line. In this way, the flow rate in the injection line is increased and the fluid density is reduced while maintaining the minimum inhibitor concentration (MIC). Attached Figure Description

[0020] Figure 1A The original scheme for injecting diluted scale inhibitor is shown, and this installation configuration caused technical problems.

[0021] Figure 1B The present invention illustrates a scheme for injecting diluted scale inhibitors.

[0022] Figure 2A It displays the pressure distribution (unit: kgf / cm²) along a distance (unit: meter). 2 (Figure 1) and an enlarged version of its first square region. The density of the injected fluid is constant, equal to r = 1120 kg / m³. 3 The distance from 0m is at the outlet of the inhibitor injection pump, and the distance from 7508m is at the chemical injection valve, which has a P=553kgf / cm². 2 The fixed fluid injection pressure.

[0023] Figure 2B This shows the pressure distribution (unit: kgf / cm²) along a distance (unit: meters). 2 (Figure 1) and an enlarged version of its first square region. The density of the injected fluid is constant, equal to r = 1110 kg / m³. 3 The distance from 0m is at the outlet of the inhibitor injection pump, and the distance from 7508m is at the chemical injection valve, which has a P=553kgf / cm². 2 The fixed fluid injection pressure.

[0024] Figure 2C This indicates that the density at the pump outlet is r = 1050 kg / m³. 3 And the fluid pressure is fixed at P=553kgf / cm. 2 The following is a simulation diagram and an enlarged version of its first square region. Figure 2C This shows the pressure distribution (unit: kgf / cm²) along a distance (unit: meters). 2 (Figure 1) and an enlarged version of its first square region. The density of the injected fluid is constant, equal to ρ = 1050 kg / m³. 3 The distance from 0m is at the outlet of the inhibitor injection pump, and the distance from 7508m is at the chemical injection valve, which has a P=553kgf / cm². 2 The fixed fluid injection pressure.

[0025] Figure 2D This is an enlarged version of the pressure distribution (in kgf / cm²) along a distance (in meters) and its first square region. The density of the injected fluid is constant, equal to r = 1035 kg / m³. 3The distance from 0m is at the outlet of the inhibitor injection pump, and the distance from 7508m is at the chemical injection valve, which has a P=553kgf / cm². 2 The fixed fluid injection pressure. Detailed Implementation

[0026] This invention claims protection for a scale inhibitor dilution system in a subsea production facility for preventing production string failure. The system comprises: a filter industrial water tank (1) connected at its outlet to a main chemical injection pump (2), the main chemical injection pump (2) controlling the flow rate of industrial water from the filter industrial water tank via a flow meter (3); and a scale inhibitor-containing storage tank (4) connected at its outlet to an auxiliary chemical injection pump (5), the auxiliary chemical injection pump (5) controlling the flow rate of scale inhibitor from the storage tank. The filter industrial water tank (1) and the scale inhibitor-containing storage tank (4) are connected in parallel via a regulating valve (6), which facilitates mixing between the two flow lines (filter industrial water and scale inhibitor) to achieve a flow rate that prevents production string (7) failure in the vertical portion of the chemical injection line (8). In this way, the flow rate and fluid density in the injection line increase while maintaining a minimum inhibitor concentration (MIC).

[0027] The present invention also claims a method for diluting a scale inhibitor in a subsea production facility to prevent failure of a production string (7), the method comprising the following steps:

[0028] (i) Fill the industrial water tank (1) with filtered industrial water and fill the scale inhibitor tank (4) with the scale inhibitor to be used in the process.

[0029] (ii) Start the main chemical injection pump (2) connected to the industrial water tank (1);

[0030] (iii) Once the water flow rate is established and stabilized, start the auxiliary chemical injection pump (5) connected to the scale inhibitor storage tank (4).

[0031] (iv) Adjust the flow rate of the pump connected to the scale inhibitor tank (4) until the desired dilution is achieved to meet the minimum inhibitor concentration requirement;

[0032] (v) Maintain the flow rate in the pump according to the well flow rate. In the event of production stoppage, the pumping of the industrial water and scale inhibitor combination is simultaneously interrupted.

[0033] Interruption of the fluid column within the tubing is characterized by excessive flow due to the pressure difference between the production tubing (7) and the injection point, leading to a decrease in the fluid level in the injection line (8). This occurs when the pressure in the production tubing is lower than the pressure in the inhibitor injection line (8). When the pressure in the injection line is higher, the pressure loss in the injection valve cannot control the flow rate, resulting in a decrease in the fluid level in the injection line. This situation is similar to what happens in a U-tube, where unbalanced pressure leads to irregular fluid flow. In other words, interruption of the fluid column within the tubing occurs when the hydrostatic pressure gradient in the metering supply line is greater than the pressure loss due to friction. Therefore, increasing the flow rate compensates for the line level to maintain continuous inhibitor injection. Well limiting and chemical injection valve adjustments are also alternatives to interruption of the fluid column within the tubing, but they are more expensive.

[0034] It is important to note that regarding the relationship between vapor pressure and fluid temperature, it is crucial to understand that chemicals injected into the well (production tubing injection) must adhere to the qualification protocol. Therefore, chemical evaporation processes that significantly alter the properties of the chemicals are not expected. Chemicals exhibiting significant evaporation within the pressure and temperature range that the fluid in the injection line will experience are not approved during the qualification process; this is one of the fundamental prerequisites for product approval in production tubing injection product programs. In short, in the case of intermittent injection, chemical evaporation is not a variable to consider. The existing problem is that the chemicals are diluted in water at an average concentration of 1000 ppm.

[0035] Steam formation occurs at near-zero pressure (extremely low pressure). The hydraulic balance between the injection line and the production string prevents the hydrostatic height of the string in the injection line from reaching the pump (remember the U-tube concept). At this point, with the pressure in the injection line near zero, steam formation occurs, as... Figure 2A and Figure 2B As can be seen in the text.

[0036] However, the discussion of intermittent injection does not focus on the conditions for steam formation, since it is clear that steam forms when the pressure approaches zero. Therefore, the curves shown indicate that the pressure in the liquid string remains continuous from the chemical injection valve to the hydrodynamic height of the string. In the case of intermittent injection, this height does not reach the pump. Therefore, in this case, the conditions leading to steam formation are not the primary concern; attention is actually focused on the hydrodynamic height of the string.

[0037] Examples and / or results obtained from the present invention

[0038] Currently, the scale inhibitor is injected at a concentration approximately one thousand times the minimum injection concentration. In the event of a disruption in the liquid column, diluting the product with industrial water does not interfere with the efficiency of the inhibition process, as dilution will maintain the minimum inhibitory concentration. All dilutions have been validated in prior laboratory tests conducted at the research center based on the product, proving to be a safe and economical method.

[0039] Inhibitor Dilution Study

[0040] simulation

[0041] In deepwater wells in the Santos Basin, intermittent inhibitor injections have been observed at different production stages, which may be caused by interruptions in the fluid column within the tubing. Possible alternatives to alleviate this intermittency include modifying the injection line, limiting production, and increasing the inhibitor flow rate. However, these alternatives require additional costs, production losses, and well intervention. Therefore, this invention proposes using a scale inhibitor diluted in water to increase the flow rate.

[0042] Figures 2A to 2D The information provided shows the pressure distribution along the injection line, with 0m located at the pump outlet. The distance 7508m refers to the delivery point of the injection line (chemical injection valve). Therefore, the presence of a liquid column interruption within the tubing is determined by the pressure value at 0m. If the pressure is zero (pressure equal to 0 kgf / cm²) at a point between 0m and 350m... 2 If the reading is 0, it is considered that the liquid column inside the tubing has been interrupted.

[0043] To verify the ability of inhibitor dilution to mitigate liquid column interruption within the column, the following simulation was proposed:

[0044] - Injection pressure at the chemical injection mandrel (P) inj The constant value is 553 kgf / cm². 2 ;

[0045] - Injected flow (Q) inj The flow rate varies between 0 l / h and 8 l / h.

[0046] - The specific mass (r) of the inhibitor is 1035 kg / m³. 3 Up to 1120kg / m 3 The changes between them.

[0047] Table 4

[0048]

[0049] When the pressure sensor indicates zero pressure but the flow sensor indicates continuous flow, an interruption in the liquid column is observed in the tubing, indicating that the phenomenon is characterized by a pressure continuity failure in the pipeline.

[0050] Figure 2D The simulation shown indicates that for r = 1035 kg / m 3 No interruption of the liquid column occurred in any of the flow simulations performed. Furthermore, the current dosage range is greater than 1000 PPM, which is higher than the recommended minimum inhibitory concentration (MIC) of 250 PPM. Therefore, dilution will not introduce significant differences regarding the recommended MIC (250 PPM to 1000 PPM). The MIC is agreed upon in advance with the manufacturer to maintain the same concentration. However, dilution must be controlled to ensure that the MIC is achieved. However, current conditions allow for a safe degree of flexibility in this control.

Claims

1. A subsea scale inhibitor dilution system for preventing production string failure, characterized by, include: A filter industrial water tank (1) is connected at its outlet to a main chemical injection pump (2), which controls the flow rate of industrial water from the tank via a flow meter (3). A storage tank (4) containing a scale inhibitor is connected at its outlet to an auxiliary chemical injection pump (5), which controls the flow rate of the scale inhibitor from the storage tank. The industrial water tank (1) and the scale inhibitor storage tank (4) are connected in parallel by a regulating valve (6), which promotes mixing between the two flow lines (industrial water and scale inhibitor) to achieve a flow rate in the vertical section of the chemical injection line (8) that prevents failure of the production line (7).

2. The system of claim 1, wherein, The scale inhibitor is diluted with water from the industrial water tank (1).

3. The system of claim 1, wherein, The auxiliary chemical injection pump (5) promotes an increase in flow rate and a decrease in fluid density in the injection line while maintaining the minimum inhibitory concentration of the scale inhibitor.

4. A method for diluting a seabed scale inhibitor for preventing failure of a production string (7), characterized in that, Includes the following steps: (i) Fill the industrial water tank (1) with filtered industrial water and fill the scale inhibitor tank (4) with the scale inhibitor to be used in the process. (ii) Start the main chemical injection pump (2) connected to the industrial water tank (1); (iii) Once the water flow rate is established and stabilized, start the auxiliary chemical injection pump (5) connected to the scale inhibitor storage tank (4). (iv) Adjust the flow rate of the pump connected to the scale inhibitor tank (4) until the desired dilution is achieved to meet the minimum inhibitor concentration requirement; as well as (v) Maintain the flow rate in the pump according to the well flow rate conditions.

5. The method of claim 4, wherein, When production stops, the flow rate in the pump is also interrupted.

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