DHSV SCALE REMOVAL METHOD IN THE PRODUCTION STRING

Abstract

The present invention addresses to a method of removing scale from the DHSV of the oil production string aiming at maintaining the production of the wells and thus avoiding the loss of production. First, a neutralizing solution is placed in the service line, before pumping the scale removing solution through the string to act on the DHSV. Next, the acid is pumped into the production string to react with the calcium carbonate scale. After the time for the dissolution of the scale inside the DHSV, the well is opened for production by the service line. The spent acid is mixed with the neutralizing solution inside the service line, reducing its corrosiveness in relation to the service line, contributing to its preservation.

Claims

1- A DHSV SCALE REMOVAL METHOD IN THE PRODUCTION STRING, characterized in that it comprises the following steps: (1) Opening the WCT valve that gives access from the production line to the interior of the production string; (2) Pumping a 1.sup.st diesel spacer cushion; (3) Pumping an alkalizer cushion in a volume 1.5 times the volume of acid that will be pumped; (4) Pumping a 2.sup.nd diesel spacer cushion with a volume equal to that of the 1.sup.st diesel cushion; (5) Pumping the DBX (diesel, butyl glycol and xylene) cushion; (6) Pumping with completion fluid to displace the front of the 1.sup.st diesel spacer cushion to the WCT, then stopping pumping; (7) Closing the WCT valve that gives access to the string; (8) Opening the WCT valve that gives access to the lift gas line; (9) Pumping, placing the 1.sup.st diesel spacer cushion, the entire alkalizer cushion and the 2.sup.nd diesel cushion to the interior of the gas lift line, in order to leave the interior of the WCT with diesel; (10) Closing the WCT valve that gives access to the lift gas line; (11) Opening the WCT valve that gives access to the production string; (12) Pumping a cushion of DBX (diesel, butyl glycol and xylene) and the acid to the interior of the production string up to the DHSV; (13) Waiting for the contact time between 30 minutes and 1 hour for the CaCO.sub.3 removal reaction; (14) Opening the WCT valve that gives access to the lift gas line; (15) Opening the well for cleaning and simultaneously pumping, through the lift gas line, the (alkaline) neutralizing solution to neutralize the acid that will be produced by the well, mixed with the oil.

2- THE METHOD according to claim 1, characterized in that the alkalizer cushion consists of caustic soda and/or sodium bicarbonate.

3- THE METHOD according to claim 1, characterized in that the acid is chosen from organic or mineral acids, such as 7% formic acid, 10% acetic acid and/or 15% hydrochloric acid.

4- THE METHOD according to claim 1, characterized in that the neutralizing solution consists of caustic soda, sodium bicarbonate or ammonium carbonate.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] The present invention will be described in more detail below, with reference to the attached figures which, in a schematic way and not limiting the inventive scope, represent examples of its embodiment. In the drawings, there are:

[0019] FIG. 1 illustrating a layout of the Stationary Production Unit (SPU) (1) connected to the well through the production riser (2) in the vertical section that continues as a production line (3) in the horizontal section to connect to the wet Christmas tree (WCT) (5) from the oil well (6) through a production line (3), a gas line (4) connected from the SPU to the WCT (5) of the well. The production of the well passes from the WCT (5) through the horizontal section corresponding to the production line (3) on the seabed, which goes until the beginning of the vertical section of the line corresponding to the production riser (2) that goes from the seabed to the SPU (1);

[0020] FIGS. 2A-2D illustrating in the upper part the side views and in the lower part the top views of the DHSV, where the fouling grows by increasing the inner ring of the DHSV valve towards the interior of the string until promoting the blocking of the inner diameter of DHSV.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The scale removal method, according to the present invention, comprises an operational sequence, by which scale removal is carried out in the DHSV, avoiding the loss of production associated with the formation of scale inside the string, without injecting removing solutions in the reservoir, helping to prevent damage to the reservoir. The purpose of this method is to place a neutralizing solution in the service line, where it will remain isolated until the end of the DHSV scale removal operation. When the well is opened for cleaning, then this solution will be used for the neutralization of the acid, by means of the synchronism of the pumping of the same by the service line with the well production.

[0022] In a second aspect, to avoid acid corrosivity in the service or gas lift line, a solution is used to neutralize excess acid that has not reacted with the calcium carbonate scale inside the string in the DHSV. In the operational sequence, before pumping the acid into the production string to act on the DHSV, the neutralizing solution is placed inside the service or gas lift line and remains inside the line until the reaction time of the acid with the scale is ended. Then, the well is opened to produce through the service line to the SPU (Stationary Production Unit). This way, the acid is neutralized when mixed with the solution, reducing the possibility of damage to the service line.

[0023] The step by step of the pumping sequence of the treatment, and the opening and closing of the valves of the wet Christmas tree (WCT), is used to plan the steps of the pumping operation and the volumetries that will be used. Information such as system volumetry, production and gas lift lines and production string, production string layout, static pressure values, flow pressure, oil viscosity, API grade, types of organic or mineral acids, neutralizing solution and fluids of displacement are used for planning the pumping operation, as well as the balancing of the fluids in order to allow the removing solution to be placed inside the string at the depth corresponding to the DHSV to guarantee the efficiency of scale removal.

[0024] The acid pumping sequence to remove DHSV fouling, in direct remote treatment from the SPU or through a stimulation boat passing through the SPU, using prior pumping of an alkalizer agent to neutralize the acid instead of injecting the same into the reservoir, according to the present invention, comprises the following steps: [0025] (1) Opening the WCT valve that gives access from the production line to the interior of the production string; [0026] (2) Pumping a 1.sup.st diesel spacer cushion; [0027] (3) Pumping an alkalizer cushion, containing caustic soda and/or sodium bicarbonate in the same concentration as the acid, in a volume 1.5 times the volume of acid that will be pumped, wherein the acid can be chosen from organic acids such as 7% formic acid or 10% acetic acid, and mineral acids such as 15% hydrochloric acid; [0028] (4) Pumping a 2.sup.nd diesel spacer cushion with a volume equal to that of the 1.sup.st diesel cushion; [0029] (5) Pumping the DBX (diesel, butyl glycol and xylene) cushion; [0030] (6) Pumping with completion fluid to displace the front of the 1.sup.st diesel spacer cushion to the WCT, then stop pumping; [0031] (7) Closing the WCT valve that gives access to the string; [0032] (8) Opening the WCT valve that gives access to the lift gas line; [0033] (9) Pumping, placing the 1.sup.st diesel spacer cushion and the entire alkalizer cushion and the 2.sup.nd diesel cushion to the interior of the gas lift line, in order to leave the interior of the WCT with diesel; [0034] (10) Closing the WCT valve that gives access to the lift gas line; [0035] (11) Opening the WCT valve that gives access to the production string; [0036] (12) Pumping a cushion of DBX (diesel, butyl glycol and xylene) and the acid to the interior of the production string up to the DHSV; [0037] (13) Waiting for a contact time of about 30 minutes for 15% hydrochloric acid, and 1 hour for 10% acetic acid and/or 7% formic acid for the CaCO.sub.3 removal reaction; [0038] (14) Opening the WCT valve that gives access to the lift gas line; [0039] (15) Opening the well for cleaning and, simultaneously, pumping, through the lift gas line, the (alkaline) neutralizing solution which can be caustic soda, sodium bicarbonate or ammonium carbonate in the same concentration of the acid that was used, 15% hydrochloric acid, 10% acetic acid and/or 7% formic acid, to promote the neutralization of the acid that will be produced by the well, mixed with the oil.

Examples

[0040] The result obtained by the invention, in a first aspect, can be measured by the recovery of the production flow rate of the wells, which always occurs in the chemical treatments carried out to eliminate calcium carbonate scales.

[0041] In a second aspect, it has the advantage of preserving the service and/or gas lift line. The objective is to carry out an operational sequence in which the service line or gas lift line is used to reserve a volume of neutralizing solution that will come into action, when the well is put into production, to neutralize the acidic solution through this line.

[0042] The present invention collaborates to maintain the production of producing fields, since it increases the MTBF of the service and/or gas lift lines due to the neutralization of the produced acid. The treatments using this technology have the advantage of injecting only the amount of solution needed to remove scale into the DHSV, reducing pumping time and well cleaning time and increasing the safety of the operation.

[0043] In addition, the possibility of using remote intervention, instead of operating with a rig, implies in cost reduction in scale management, in interventions for scale removal by injection of acidic removers.

[0044] It should be noted that, although the present invention has been described in relation to the attached drawings, it may undergo modifications and adaptations by technicians skilled on the subject, depending on the specific situation, but provided that it is within the inventive scope defined herein.