A completion fluid should not be damaging to the formation, should be solid free, and its weight can vary over a wide range. There is an organic fluid1  that is reusable after recuperating it with a brine and has low toxicity and corrosiveness. Given all these properties, we decided to evaluate it as a completion fluid.

This reusable organic fluid is prepared by dilution of a concentrated very viscous organic base with a low viscosity and toxicity oil to reach concentrations in the range of 9 to 16 ppg.

The permeability tests were conducted in a Hassler type cell using the organic fluid (15.7 ppg) within different sequences of fluids, as is shown in Tables 1 and 2. All the tests were performed at 320°F with cores and oil from Naricual Formation (Venezuela) and soaking times of 3 hrs for mud filtrate or calcium brine and 16 hrs for the organic fluid.

The results in Table 1 show that the organic fluid by itself does not damage the formation but instead is capable of cleaning it, allowing a better mobility of the oil. If the calcium brine (11 ppg) will follow the organic fluid into the formation, a damage of near 30% will appear; this damage can be reduced to almost zero by adding 1% of a surfactant to the brine.

A severe impairment to the oil mobility appeared when mud filtrate had leaked into the formation, which in all three cases shown in Table 2, is enlarged by the calcium brine. The use of the organic fluid as completion fluid partially removed the damage made by the water-based mud filtrates, but it did not clean or added damage in the oil-based mud case.

Table 2 shows a further reduction in the mobility of oil in all three cases if calcium brine goes into the formation after the organic fluid and the mud filtrate; these reductions are not as severe as when no organic fluid was used. Table 2 also shows that the addition of 1% surfactant to the brine lowers the additional damage in all the cases; the effect is more pronounced for the water-based muds.

From the data of this evaluation can be concluded that:

  1. The use of this low toxicity organic fluid for completion will partially clean the damage caused by water-based mud filtrates in the formation. The organic completion fluid will not increase the damage produced by the oil-based mud.

  2. The use of calcium brine with 1% of surfactant seems the best way to recover the organic fluid in order not to loose the reduction of damage gained by the organic completion fluid.

A completion fluid should not be damaging to the formation, should be solid free, and its weight can vary over a wide range. There is an organic fluid1  that is reusable after recuperating it with a brine and has low toxicity and corrosiveness. Given all these properties, we decided to evaluate it as a completion fluid.

This reusable organic fluid is prepared by dilution of a concentrated very viscous organic base with a low viscosity and toxicity oil to reach concentrations in the range of 9 to 16 ppg.

The permeability tests were conducted in a Hassler type cell using the organic fluid (15.7 ppg) within different sequences of fluids, as is shown in Tables 1 and 2. All the tests were performed at 320°F with cores and oil from Naricual Formation (Venezuela) and soaking times of 3 hrs for mud filtrate or calcium brine and 16 hrs for the organic fluid.

Table 1

Results of the Permeability Tests Performed at 320°F Without Mud Invasion.

Fluid(s) per TestDamage (%)
Organic Fluid -22 
Organic Fluid Calcium Brine 29 
Organic Fluid Calcium Brine (1% surf.) -4 
Fluid(s) per TestDamage (%)
Organic Fluid -22 
Organic Fluid Calcium Brine 29 
Organic Fluid Calcium Brine (1% surf.) -4 
Table 2

Results of the Permeability Tests Performed at 320°F With Invasion of Different Muds Filtrates.

Fluid(s) per TestDamage (%) Oil-Based MudDamage (%) Water-Based Mud ADamage (%) Water-Based Mud B
Mud Filtrate 83 42 79 
Mud Filt. Calcium Brine 96 78 91 
Mud Filt. Organic Fluid 79 32 
Mud Filt. Organic Fluid Calcium Brine 84 51 42 
Mud Filt. Organic Fluid Calcium Brine (1% surf.) 79 36 28 
Fluid(s) per TestDamage (%) Oil-Based MudDamage (%) Water-Based Mud ADamage (%) Water-Based Mud B
Mud Filtrate 83 42 79 
Mud Filt. Calcium Brine 96 78 91 
Mud Filt. Organic Fluid 79 32 
Mud Filt. Organic Fluid Calcium Brine 84 51 42 
Mud Filt. Organic Fluid Calcium Brine (1% surf.) 79 36 28 

The results in Table 1 show that the organic fluid by itself does not damage the formation but instead is capable of cleaning it, allowing a better mobility of the oil. If the calcium brine (11 ppg) will follow the organic fluid into the formation, a damage of near 30% will appear; this damage can be reduced to almost zero by adding 1% of a surfactant to the brine.

A severe impairment to the oil mobility appeared when mud filtrate had leaked into the formation, which in all three cases shown in Table 2, is enlarged by the calcium brine. The use of the organic fluid as completion fluid partially removed the damage made by the water-based mud filtrates, but it did not clean or added damage in the oil-based mud case.

Table 2 shows a further reduction in the mobility of oil in all three cases if calcium brine goes into the formation after the organic fluid and the mud filtrate; these reductions are not as severe as when no organic fluid was used. Table 2 also shows that the addition of 1% surfactant to the brine lowers the additional damage in all the cases; the effect is more pronounced for the water-based muds.

From the data of this evaluation can be concluded that:

  1. The use of this low toxicity organic fluid for completion will partially clean the damage caused by water-based mud filtrates in the formation. The organic completion fluid will not increase the damage produced by the oil-based mud.

  2. The use of calcium brine with 1% of surfactant seems the best way to recover the organic fluid in order not to loose the reduction of damage gained by the organic completion fluid.

This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A. Telex, 163245 SPEUT.

We would like to thank OSCA and OSCA de Venezuela for kindly providing us with the necessary samples to run these tests.

Ogilvy
,
N.
: "
Well Bore Fluid
,"
U.S. Patent No. 4,900,456
(
1990
).