EMULSION PREVENTERS FOR COMPLETION AND STIMULATION FLUIDS

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1 EMULSIN PREVENTERS FR CMPLETIN AND STIMULATIN FLUIDS Thiago Vinícius Alonso Research and Development Engineer - Dow Brasil S/A ABSTRACT Alkoxylated polymers are widely used as demulsifiers agents for crude oil in off-shore and on-shore operations. At this work some demulsifiers bases and its respective synergic mixtures had been evaluated as emulsion preventers in saline completion fluids and acid stimulation fluids. Completion fluids are just used after the cementing operation, where this fluid must be free of solids and it is used to control the well during the completion process. The fluid is prepared to do not harm the permeability of the formation and to promote the density capable to provide higher hydrostatic pressure to the static pressure of the reservoir. Typically brines of 8.4 the 19.2 lb/gal are used for solutions containing salts like KCl, NaCl, CaCl 2 among others. Basically the acid stimulation fluid has the objective to increase the oil productivity of the well. The fluid consists of an acid solution, usually of hydrochloric, hydrofluoric and formic acids. The acid fluid basically will act breaking and generating fissures in the rock formation increasing the permeability of this and increasing oil outflow. Mainly for carbonate rocks these acidizing methods are used. For sandstone formations the solutions of hydrofluoric acid are more recommended by its power to dissolve silica. Some basic characteristics are necessary for the chemical agent which is considered to act as emulsion preventer for this application, such as compatibility with acid/saline fluids, stability of the mixture from the point of view of do not show phase separation and mainly to prevent the emulsion of the fluids with the considered oil. Typically Nonyl-Phenol Ethoxylated with high degree of ethoxylation is used as emulsion preventer today. The polymers developed by DW promote high efficiency of breaking between the fluid and the crude oil for small dosages and in fast way. At the present work the performance of the optimized formulations are described. INTRDUCTIN Emulsion preventers mainly have the objective to avoid emulsification at the well bore of the completion fluid used after cementing operation and also the stimulation fluid used to increase well productivity. Basically these fluids are: Completion fluid is a saline fluid based on sea water (98%) and some chemicals (2%), where emulsion preventers represent 0.2% - 0.6%. It is used in the crude oil exploration at the initial stage, mainly for new wells.

2 IBP468_09 EMULSIN PREVENTERS FR CMPLETIN AND STIMULATIN FLUIDS Acid Stimulation fluid is an acid aqueous solutions based on HCl, acetic, formic and hydrofluoric acid, in several concentrations (5%, 10%, 15% and 20%) and other materials such as clay. It is used to increase and enhance the oil production. Emulsion Definition: An emulsion is a combination of two liquids that do not mix under normal conditions. In an emulsion one of the liquids is spread out or dispersed throughout the other in the form of droplets. A stable emulsion is an emulsion that will not break down without some form of treating. Desemulsification Mechanism demulsifiers have the capability to complex with Asphaltene molecules considered as most prominent emulsifiers in crude oils. The demulsifier is a surface active agent or a surfactant and migrates thought the continuous phase to the oil interface. As a typical demulsifier is a formulation of several chemistries such as alkyl phenol formaldehydes, Polyalkylene glycols and Epoxy/Polyol adducts; some molecules acts moving to the interface of the water droplet aligns itself and disrupting and weakening emulsifier film. The picture below illustrates the mechanism of Asphaltene complexation by demulsifiers Unstable emulsion results when the interfacial film between the dispersed phase can be eliminated leading to droplet coalescence and subsequent separation of the oil and water phase. This unstabilization mechanism can be accomplished by mechanical, electrical and chemical methods. Mechanical and electrical methods usually consist in heating, electrostatic precipitation and filtration. Chemical demulsification requires low capital and provides flexibility for changing or modification to address emulsion problems. Some theories have been proposed to explain the effects of these chemicals in emulsions. The most common theory suggests that demulsifiers weakens the emulsifying film around the water droplet in a water in oil emulsion. ther theories say that Fig. 1 Asphaltenes complexation and emulsion unstabilization

3 IBP468_09 EMULSIN PREVENTERS FR CMPLETIN AND STIMULATIN FLUIDS Typical molecules used in demulsifier systems are CH 3 R CH 2 CH 2 CH Fig. 2 - Alkyl Phenol Formaldehyde Alkoxylated I C H 2 C H C H 3 R 1 C H 2 C H 2 Fig. 3 - Alkoxylated block copolymers EXPERIMENTAL METHDLGY The experiments followed PETRBRAS methodology NC This standard prescribes the evaluation method for emulsion preventer tensoactives used in crude oil wells completion and stimulation fluids. x n y H H m Test Fluid The test fluid was prepared in laboratory with same additives and same water from field. The emulsion preventer is added to the selected fluid for the evaluation. The test fluid can be a saline or acid solution, viscosified or not. The fluids tested were: Acid MUDACID HCl 7.5% HCl 10% Acetic Acid/ Formic Acid 5% / 7% Saline CAMAI 8.6 CAMAI 9.0 The tested emulsion preventer was added to the studied fluid with its respective concentration, as illustrated in picture below. Fig.4 Test Fluid Preparation

4 % Separation % Separation IBP468_09 EMULSIN PREVENTERS FR CMPLETIN AND STIMULATIN FLUIDS The acid fluids basically consisted in a mixture of the correspondent acids with industrial water and additives and the saline fluids consisted in a blend of potassium chloride in sea water with some additives ALBACRA oil / MUDACID fluid 50 The test was conducted in a ratio of 3:1 3 parts of oil for 1 part of the studied fluid Temperature considered was 60 C. RESULTS AND DISCUSSIN Several crude oils, primarily medium to light crudes with API gravity varying from 20 to 30 were tested. The crude oil comes from the off shore platforms at the producer region of Bacia de Campos Brasil. DEMTRL PE 37 Emulsion Preventer was designed to work for acid solution and DEMTRL PE 35 Emulsion Preventer was designed to work for saline solution. The water/oil separation effectiveness of the emulsion preventers tested can be compared at the separation charts. 0 DEMTRL PE 37 - Conc. 0.5% DEMTRL PE 37 - Conc. 0.8% Baseline - Conc. 0% Fig. 5 Emulsion Reduction curve for DEMTRL PE 37 ALBACRA oil/ MUDACID fluid It is noticeable that DEMTRL PE 37 showed fast separation characteristics at this test. Although 0.5% of concentration in acid fluid demonstrated the fastest emulsion break at the beginning of the test, the concentration of 0.8% achieved the maximum separation level in 15 minutes of test while the lower concentration showed to achieve the maximum separation in 30 minutes. DEMTRL PE 37 was tested also in a concentration of 0.5% using the HCl 10% acid fluid and the ALBACRA crude oil. Acid Solution: DEMTRL PE 37 was tested in a concentration of 0.5% and 0.8% in the acid fluid - MUDACID using the ALBACRA crude oil ALBACRA oil / HCl 10% fluid DEMTRL PE 37 - Conc. 0.5% Baseline - Conc. 0% Fig. 6 Emulsion Reduction curve for DEMTRL PE 37 ALBACRA oil/ HCl 10% fluid

5 % Separation % Separation IBP468_09 EMULSIN PREVENTERS FR CMPLETIN AND STIMULATIN FLUIDS DEMTRL PE 37 showed that maximum separation level for 0.5% of concentration for 15 minutes, breaking 95% of the emulsion generated. The picture below shows the appearance of the bottle used in bottle test for DEMTRL PE 35 in this case. Saline Solution: DEMTRL PE 35 was tested in a concentration of 0.2%, 0.3% and 0.4% in the saline fluid CAMAI 9.0 using the ESPADARTE 17 crude oil ESPADARTE 17 oil / CAMAI 9.0 fluid Fig. 8 Bottle test for DEMTRL PE 35 ESPADARTE 17 oil/ CAMAI 9.0 fluid DEMTRL PE 35 - Conc. 0.4% DEMTRL PE 35 - Conc. 0.3% Baseline - Conc. 0% DEMTRL PE 35 - Conc. 0.2% Fig. 7 Emulsion Reduction curve for DEMTRL PE 35 ESPADARTE 17 crude oil / CAMAI 9.0 fluid DEMTRL PE 35 was tested in a concentration of 0.1%, and 0.2% in the saline fluid CAMAI 9.0 using the ALBACRA 13 crude oil ALBACRA 13 oil / CAMAI 9.0 fluid DEMTRL PE 35 showed fast separation results for concentrations above 0.3%. For 0.4% and 0.3% of concentration the emulsion break was fast for the first 5 minutes of test. The best result was achieved for 0.4% of concentration, where maximum separation was achieved for 5 minutes and remained constant for the rest of the test. The concentration of 0.2% demonstrated to be efficient to break the emulsion but the speed to break it was much lower compared to the other studied concentrations. In this case maximum emulsion break was found for 20 minutes of test DEMTRL PE 35 - Conc. 0.1% DEMTRL PE 35 - Conc. 0.2% Baseline - Conc. 0% Fig. 9 Emulsion Reduction curve for DEMTRL PE 35 ALBACRA 13 oil/ CAMAI 9.0 fluid It can be seen that emulsion generated with ALBACRA 13 oil is more stable

6 % Separation IBP468_09 EMULSIN PREVENTERS FR CMPLETIN AND STIMULATIN FLUIDS compared to other crude oils as the maximum separation achieved was 48% for 30 min of test and using 0.2 % of DEMTRL PE 35. The usage of 0.1% of preventer showed not so good results as can be seen low emulsion break rate. Another test was conducted to ESPADARTE RJS 499 oil and the saline CAMAI 8.6 fluid ESPADARTE RJS 499 oil / CAMAI 8.6 fluid DEMTRL PE 35 - Conc. 0.4% Baseline - Conc. 0% Fig. 10 Emulsion Reduction curve for DEMTRL PE 35 ESPADARTE RJS 499 oil/ CAMAI 8.6 fluid By the tests done, almost 100% of emulsion separation was achieved using a concentration of 0.4% of DEMTRL PE 35 with the saline fluid. The time needed to break the emulsion was around 30 minutes of test. CNCLUSINS For acid fluids the product DEMTRL PE 37 showed excellent performance for the fluids HCL 10% and MUDACID indicating the separation of phases around 96% for both fluids for concentration above 0.5%. Higher concentrations of preventer implicated in faster time to break the emulsion. For saline fluids the product DEMTRL PE 35 showed good performance for the CAMAI 8.6 and CAMAI 9.0 solutions. The performance was better for the oil proceeding from ESPADARTE area where 0.2% of product was enough to break 90% of emulsion for CAMAI 9.0 fluid. The oil from ALBACRA showed best results for 50% of emulsion break in some tests. The emulsion in this case seems to be more stable perhaps due to the high presence of Asphaltene compounds one of the noticeable responsible to stabilize the emulsions. At the results presented it is seen that the performance of preventer is increased when concentration is increased. ther tests with higher concentration were not done due to lack of time in field. REFERENCES TREATING ILFIELD EMULSINS, fourth edition, Petroleum Extension Service, The University of Texas at Austin, 1990