SYSTEM AND METHOD FOR DILUTING SUBSEA SCALING INHIBITOR TO PREVENT PRODUCTION STRING BREAKDOWN

Description

RELATED APPLICATIONS

This application claims the benefit of priority to Brazilian Patent Application No. 1020240272579, filed Dec. 26, 2024, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention has as its field of application the area of oil exploration and production. More specifically, the present invention falls within the area of reservoir management, within the technologies of scaling management, lift and flow in order to guarantee flow and maintenance of production.

BACKGROUND OF THE INVENTION

The formation of scaling, that is, solid precipitates that form in aqueous systems when, due to changes in the physical or chemical environment of the system, the solubility limits of some components are exceeded, is a problem in many industrial operations involving aqueous fluids, for example, in the oil and gas industry, mining, paper manufacturing and geothermal power generation.

In the oil and gas industry, in particular, the deposition of scaling on equipment surfaces can cause obstructions or blockages, leading to costly production interruptions and safety risks arising from the unexpected buildup of pressure. In oil and gas wells and associated equipment such as wellheads, flowlines, production strings, or other processing and transportation equipment, scale formation occurs primarily due to destabilization through pressure and temperature changes in the formation water and the mixing of incompatible aqueous fluids. For example, when seawater is used as an injection fluid to drive oil through a subsea formation toward a production well, differences in the ionic content of the injected seawater and the ionic content of the native water of the formation can produce the precipitation of organic salts.

In the absence of proper treatment, the precipitated salts form scale that obstructs the flow of oil toward the production wells and accumulates on the production equipment, ultimately leading to blockage of the production well. Similarly, precipitated salts can form accumulated scale on equipment associated with the production, processing, and transportation of hydrocarbons.

To avoid such obstructions, scale inhibitors are widely used in the oil and gas industry, and scale problems on equipment surfaces can be solved by continuously injecting scale inhibitors into the equipment.

To prevent scale formation within oil/gas transport formations, two techniques are generally used. In one technique, a scale inhibitor can be included in a fluid, usually aqueous, to be injected into the formation through one or more injection wells, for example, to discharge oil towards a production well (water flooding treatment). In another technique, known as “compression treatment,” a fluid containing a scale inhibitor (again typically an aqueous fluid) can be introduced into a production well (after production has ended) so as to “compress” the scale inhibitor into the rock formation surrounding the production well. Thus, scale inhibitors are supplied to the formation rock in order to prevent the formation of scale deposits both in the formation itself (pore blockage) and subsequently in the downstream production apparatus.

Scale formation can only be controlled if a scale inhibitor is supplied in sufficient amount. In the case of “compression treatment,” the concentration of the scale inhibitor will decrease over time until repeated treatment with the scale inhibitor is necessary (a “recompression” treatment). It is therefore very useful to analyze the fluid produced from a production well in order to ensure that the concentration of the scale inhibitor is always maintained at a level where scale formation is sufficiently inhibited. By analyzing the level of scale inhibitor in the produced fluids, the depletion of the inhibitor concentration can be monitored and, therefore, the need for repeated treatments with scale inhibitors can be determined. It is desirable that the level of scale inhibitors be determined accurately as a precaution against the risk of scale deposition and consequent loss of production. On the other hand, supplying more scale inhibitor than is necessary is undesirable, both from the point of view of the cost of the excess scale inhibitor and the interruption of production that is necessary every time a new compression treatment is performed.

Given this scenario, the technical problem that motivated the invention was the need to increase the flow rate of the scale inhibitor to compensate for a possible discontinuity in the hydraulic connection, referred to here as “string breakdown”.

However, as already mentioned, such an increase promotes unnecessary expenditure of chemical product. The solution achieved by the invention was the dilution of the scale inhibitor product to a minimum concentration necessary to avoid string breakdown, reducing the specific mass of the solution and maintaining the injection above the minimum inhibitory concentration (MIC, minimum injection concentration). The discontinuity of the hydraulic connection, also known as string breakdown, occurs when the hydrostatic gradient in the dosing line is greater than the pressure drop due to friction.

Diluting the inhibitor concentration solves the problem of string breakdown in two ways. First, dilution seeks to reduce the fluid density in the dosing line, decreasing the hydrostatic gradient of the line and allowing work with a wider range of string bottom pressures. Second, inhibitor dilution controls product consumption, since the minimum required inhibitor concentration will be maintained, without excessive product injection.

Therefore, the present invention seeks to stabilize the string in the chemical injection line during inhibitor injection operation. The invention will be applied in parallel with the chemical injection system, providing volumetric support to prevent the phenomenon of string breakdown. The diluting fluid used is water, and the invention is based on the principle of maintaining the minimum injection concentration and providing an additional flow rate that prevents string breakdown from occurring.

Expected Advantages

The economic advantage is related to the savings that will be achieved by avoiding the waste of chemical product (scaling inhibitor), with the increase in the inhibitor flow rate as a way to avoid string breakdown during the pumping of the scale inhibitor. Productivity is related to maintaining the pumping of scale inhibitor, thus avoiding the formation of scale and consequently the loss of production associated with the blockage of the production string of the well.

The health and safety advantage is related to the simplicity of the adaptation operation, without needing intervention in the well. All changes are made at the platform level, without the need for rig movement and higher-risk operations.

String breakdown promotes loss of control over the volume of inhibitor injected into the well, due to the intermittency of the product injection. Intermittency can lead to an interruption of the inhibition process that can last on the order of hours to days. Intermittency in the injection of scale inhibitor promotes discontinuity in the scale inhibition process, allowing scale formation to occur in the production string of the well, which can lead to blockages in the oil production of the well. The invention thus promotes increased reliability of the scale inhibition process, since in addition to increasing control of the chemical injection process, it ensures that well production is not reduced due to the presence of scale in the production string.

The prevention of scale formation guaranteed by the continuous and uninterrupted injection of scale inhibitor ensured by the invention allows for stable and controlled well production, maintaining production levels that guarantee the delivery of value to Brazilian society.

Furthermore, the increased flow rate resulting from the parallel or series connection of pumps is one of the possible alternatives. The increased flow rate promotes an increase in pressure losses in the line, which would be one of the possible alternatives for solving the problem. However, this alternative has technical and economic limitations. To achieve the necessary pressure loss to avoid flow intermittency, we may need excessively high flow rates which, in addition to potentially interfering with the flow pattern in the production string, are a waste of inhibitor product, characterizing a less economically attractive solution.

SUMMARY OF THE INVENTION

The present invention comprises a method for diluting scaling inhibitor in subsea production equipment to prevent breakdown of the production string and a system.

The original system consists of the main chemical injection pump and the scaling inhibitor connected to the chemical injection mandrel of the platform, as shown in FIG. 1A. In the proposed invention, the auxiliary chemical injection pump is connected in parallel with the main chemical injection pump through the manifold to promote mixing between the two flow lines (filtered industrial water and scale inhibitor), in order to achieve a flow rate that prevents string breakdown in the vertical portion of the injection line. In this way, the flow rate is increased and the fluid density in the injection line is decreased within a range that maintains the minimum inhibitory concentration (MIC).

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows the original scheme for injecting scale inhibitor with dilution, the installed configuration that caused the technical problem.

FIG. 1B shows the scheme for injecting scale inhibitor with dilution proposed by the present invention.

FIG. 2A is a graph showing a pressure profile in kgf/cm² along the distance in meters and its enlarged version of the first square. The density of the injected fluid is constant and equal to ρ=1120 kg/m³. The distance 0 m is located at the outlet of the inhibitor injection pump, and the distance 7508 m is located at the chemical injection valve, which has a fixed fluid injection pressure of P=553 kgf/cm².

FIG. 2B is a graph showing a pressure profile in kgf/cm² along the distance in meters and its enlarged version of the first square. The density of the injected fluid is constant and equal to ρ=1110 kg/m³. The distance 0 m is located at the outlet of the inhibitor injection pump, and the distance 7508 m is located at the chemical injection valve, which has a fixed fluid injection pressure of P=553 kgf/cm².

FIG. 2C is a graph showing the simulation for a density ρ=1050 kg/m³ at the pump outlet with the fluid pressure fixed at P=553 kgf/cm² and its enlarged version of the first square. FIG. 2C is a graph showing a pressure profile in kgf/cm² along the distance in meters and its enlarged version of the first square. The density of the injected fluid is constant and equal to ρ=1050 kg/m³. The distance 0 m is located at the outlet of the inhibitor injector pump, and the distance 7508 m is located at the chemical injection valve, which has a fixed fluid injection pressure of P=553 kgf/cm².

FIG. 2D is a graph showing a pressure profile in kgf/cm² along the distance in meters and its enlarged version of the first square. The density of the injected fluid is constant and equal to ρ=1035 kg/m³. The 0 m distance is located at the outlet of the inhibitor injection pump, and the 7508 m distance is located at the chemical injection valve, which has a fixed fluid injection pressure of P=553 kgf/cm².

DETAILED DESCRIPTION OF THE INVENTION

The present invention claims protection for a scaling inhibitor dilution system in subsea production equipment to prevent production string breakdown. The system consists of a filtered industrial water tank (1) connected at its outlet to a main chemical injection pump (2) that controls the flow rate of industrial water coming from the tank through a flow meter (3); a tank containing the scaling inhibitor (4) connected at its outlet to an auxiliary chemical injection pump (5) that controls the flow rate of the scaling inhibitor coming from the tank. Both filtered industrial water tanks (1) and scale inhibitor tanks (4) are connected in parallel through a regulating valve (6) that promotes mixing between the two flow lines (filtered industrial water and scale inhibitor), in order to achieve a flow rate that prevents breakdown of the production string (7) in the vertical portion of the chemical injection line (8). In this way, the flow rate is increased and the fluid density in the injection line is decreased within a range that maintains the minimum inhibitory concentration (MIC).

The present invention further claims protection for a method of diluting scale inhibitor in subsea production equipment to prevent breakdown of the production string (7), the method comprising the following steps:

• • (i) filling the industrial water tanks (1) with filtered industrial water and filling the inhibitor tank (4) with the scale inhibitor that will be used in the process;
  • (ii) starting the main chemical injection pump (2) connected to the industrial water tank (1);
  • (iii) with the water flow established and stable, starting the auxiliary chemical injection pump (5) connected to the scale inhibitor tank (4);
  • (iv) regulating the flow of the pump connected to the inhibitor tank (4) until the desired dilution is achieved, so that the MIC is respected;
  • (v) the flow in the pumps is maintained dependent on the well flow conditions. In cases of production stoppage, the pumping of the industrial water+inhibitor combination is interrupted concomitantly.

String breakdown is characterized by a reduction in the fluid level in the injection line (8) due to excessive flow, which occurs due to the pressure difference between the production string (7) and the injection point. This phenomenon occurs when the pressure in the production string is lower than the pressure in the inhibitor injection line (8). When the pressure in the injection line is too high, the pressure losses in the injection valve are unable to control the flow, resulting in a decrease in the fluid level in the injection line. This situation is similar to what occurs in a U-tube, where unbalanced pressure causes irregular fluid flow. In other words, string breakdown occurs when the hydrostatic gradient in the dosing line is greater than the pressure loss due to friction. Therefore, increasing the flow rate compensates for the line level, maintaining continuous injection of the inhibitor. Well restriction and adjustment of the chemical injection valve would also be alternatives to string breakdown, but they are more expensive.

It is worth noting that regarding vapor pressure×fluid temperature, it is important to understand that the chemicals injected into the well (production string injection) are subject to a qualification protocol. Therefore, the evaporation process of the chemical that significantly modifies its properties is not expected. Chemicals that exhibit substantial evaporation within the pressure and temperature range to which the fluids in the injection line will be subjected are not approved in the qualification process, this being one of the basic premises for product approval in the production string injection product protocol. In short, chemical evaporation is not a variable to be considered in cases of intermittent injection. The existing problem is that they are diluted in water, at an average ratio of 1000 ppm.

Vapor formation occurs at pressures close to zero pressure (excessively low pressures). The hydraulic equilibrium 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). It is at this point, where the pressures in the injection line approach zero, that vapor formation occurs, as can be seen in FIG. 2A and FIG. 2B.

However, the discussion on intermittent injection does not focus on the conditions for vapor formation, as it is clear that vapor forms when pressures are close to zero. Thus, the profiles shown demonstrate that the pressure in the liquid string remains continuous, from the chemical injection valve to the hydrodynamic height of the string. In cases of intermittent injection, this height does not reach the pump. Therefore, the condition that leads to vapor formation is not the main concern in this context; attention is actually focused on the hydrodynamic height of the string.

EXAMPLES AND/OR RESULTS OBTAINED FROM THE INVENTION

Currently, the injection of the scale inhibitor is carried out in concentrations on the order of a thousand times the minimum injection concentration. Diluting the product with industrial water in cases of string breakdown will not interfere with the efficiency of the inhibition process, since the dilution will maintain the minimum inhibitory concentration. All dilutions were validated in laboratory tests carried out in advance according to the product at the research center, proving to be a safe and economical approach.

Inhibitor Dilution Study

Simulations

In a deepwater well in the Santos Basin, intermittent inhibitor injection was observed during various production periods, and this may have been the cause of string breakdown. Possible alternatives to mitigate this intermittency would be changing the injection line, restricting production, and increasing the inhibitor flow rate. However, these alternatives entail additional costs, production losses, and interventions in the well. Thus, the present invention proposes increasing the flow rate using a scale inhibitor diluted in water.

The information provided in FIGS. 2A to 2D shows a pressure profile along the injection line, where the 0 m distance is at the pump outlet. The 7508 m distance refers to the delivery point of the injection line (chemical injection valve). Thus, whether or not there is a string breakdown is determined by the pressure value at the 0 m distance. If the pressure is zero (pressure equal to 0 kgf/cm²) at some point near the distance 0 to 350 m, it is said that string breakdown occurs.

To validate the ability of inhibitor dilution to mitigate string breakdown, the following simulations were proposed:

• • Injection pressure (P_inj) at the chemical injection mandrel constant at 553 kgf/cm²;
  • Injection flow rates (Q_inj) varying between 0 and 8 l/h;
  • Specific mass of the inhibitor (r) varying between 1035 and 1120 kg/m³.

String breakdown is observed when pressure sensors indicate zero pressure, but flow sensors indicate continuous flow, showing that there is a failure in pressure communication in the line that characterizes the phenomenon.

The simulations shown in FIG. 2D show that there was no string breakdown in any of the flow simulations performed for ρ=1035 kg/m³. In addition, the current dosage range is greater than 1000 PPM, a value higher than the recommended minimum inhibitory concentration of 250 PPM. Therefore, dilution does not bring significant differences regarding the recommended minimum inhibitory concentration, which will be between 250 PPM and 1000 PPM. The minimum inhibitory concentration is previously agreed with the manufacturer so that the same concentration is maintained. Nevertheless, it is essential to control the dilution to ensure that the minimum inhibitory concentration is met. However, current conditions allow for safe flexibility in this control.