TREATMENT OF THE NEAR-WELLBORE AREA WITH EZY-FLOW BREAKER SYSTEM DURING OPEN-HOLE COMPLETION

TREATMENT OF THE NEAR-WELLBORE AREA WITH EZY-FLOW BREAKER SYSTEM DURING OPEN-HOLE COMPLETION

Nowadays well drilling at most fields is performed with biopolymer drilling fluids that contain structure-forming agents (biopolymer), fluid-loss control additives (starch), and bridging agents of different sizes (chalk) and are able to meet certain well construction requirements, such as formation of a firm impermeable filter cake. However, when the well is being brought into production the presence of the solids-laden filter cake in the open hole can be one of the reasons for accelerated productivity loss.

In view of the abovementioned, Oilfield Services Company AKROS decided to design a complex breaker system in their laboratory of drilling fluids and process fluids that will enable removing the filter cake after drilling with biopolymer fluids.

The following criteria were used to design a breaker system:

- Ability to destroy filter cake (with an acid-soluble bridging agent as the mechanical frame and a starch agent as the structural bond);

- Compatibility with all process fluids and formation fluids;

- 4 to 24 hours of delay (a breaker system must be generated directly in the spotting interval);

- Zero negative effect on the rock matrix;

- Low corrosiveness;

- Efficient at the formation temperature of 18-110 degrees;

- pH factor of an original formulation – 4 or higher.

To determine the effectiveness of the formulation designed as per these criteria and set objectives, several breaker systems were tested in the laboratory. At the selection stage, tests were performed for 12 filter cake breakers that included different complex components. The test results showed that only one formulation met all of the criteria. The following agents were used as components of the breaker:


Product

Description

Function

EZY-SOLV FA

Precursor

Low organic acid generating agent

EZY-BUF

рН buffering agent

Reaction rate control

EZY-SURF

Non-ionic surfactant

Improved penetration of chemicals into the cake structure

EZY-ZYM

Enzyme

Starch destruction



TESTING PROCEDURE

EZY-FLOW breaker system was tested for the ability to destroy filter cake formed by the AKROS biopolymer mud.

The mud was mixed based on standard concentrations used for drilling a producing zone in real projects. The bentonite powder was used to imitate a contaminant (solids).

The appearance was a clear liquid without any strong odor (Picture 1). The original formulation had a predominantly neutral рН of 6-6.5:


Picture 1. EZY-FLOW Breaker System

рис 1-1_cut.jpg EZY FLOW рис 1-2.jpg


The 20µm ceramic disks were used for determining the breaker effectiveness.

The HPHT filter press and mud samples were used to form filter cakes on a 20µm ceramic disk (OFITE catalog) (Picture2)


Picture 2. Filter cake

рис 2-1_cut.jpg Фильтрационная корка рис 2-2.jpg


The ceramic disk with the formed filter cake was put into a glass vessel filled with EZY-FLOW, after which the prepared sample was kept in the heated oven at 80, 95, and 110 degrees and then at room temperature.

Testing for starch and calcium carbonate destruction was carried out after the ceramic disk remained in the breaker system for 24 hours.

Testing for starch destruction was performed by applying 5% iodine solution to the filter cake. When the iodine solution reacts with starch, it will change its color to brilliant blue.

Testing for calcium carbonate destruction was done by applying 15% HCl. Where calcium carbonate is present, the reaction will include bubbling.

Test results:

  Photo       Description 
   

Reaction within 24 hours

 табл 1_cut.jpg        1. There was no reaction for 3 hours; bubbling started in 3 hours while violent reaction began in 4 hours. Visual observation showed breaking up of 95% filter cake.   

         

Reaction within 24 hours

 табл 2_cut.jpg      2. Testing for calcium carbonate did not show any calcium carbonate in the filter cake.

           

Reaction within 24 hours

 табл 3_cut.jpg      3. Testing for starch did not show any starch in the filter cake. The reaction color was light brown. 


EZY-FLOW acid-generating formulation displayed the best lab test results, specifically:

1. The filter cake formed on the base of a biopolymer fluid was broken up to 99%;

2. The formulation allows adjusting the start of the reaction to 4-24 hours. Moreover, unlike other breaker systems, reaction start and end time can be adjusted within different and independent time intervals;

3. Corrosiveness of the formulation does not exceed 0.12 mm/year which is the industry standard;

4. The original formulation has pH of 6-6.5;

5. The formulation is inert to both process fluids as well as formation water and oil.


Summary:

Oilfield Services Company AKROS designed and tested the product that can be used for cleaning the near-wellbore zone from debris in order to improve well productivity.

The formulation was successfully tested in the drilling fluids research laboratory of SamaraNIPIneft (Rosneft Oil Company), the research laboratory of Surgutneftegaz (Fedorovskneft Oil&Gas Production Department), and the drilling fluids and cementing slurries laboratory of Gazpromneft (Giprotyumenneftegaz,  Gazpromneft Engineering-Research Center, Gazpromneft-Shelf) and is recommended for application. 


Authors:

Maxim Tereshchuk, Business Development Manager, AKROS

Pavel Nikitin, Senior Manager of the Completion Department, RN-Center for Expert Support & Technological Development 


Source:  "Burenie i neft'", 2018, № 3, 44