US2354203A - Method of treating wells - Google Patents

Description

retested dul as,

attests estates nurses or rename warns Allen is. Garrison, Houston, Tex, assiguor, by mesne assignments, to The Texas Company, New Yorls. N. Y., a corporation or Delaware No Drawing. Application January 30, 1941,

Serial No. 376,652

14 Claims.

increase the ratio of oil relative to water pro-' duced from the well.

It is commonly recognized that oil producing sands are invariably water-wet and that the adsorbed water films on the sand grains facilitate the flow of water and resist the flow of oil through the formation. This resistance to the oil flow limits the passage of the oil to the pore spaces of the larger interstices and even these pore spaces are reduced in volume by the water films on the adjoining sand grains, Where this condition is prevalent, the well produces both water and oil, and after some time the formation water advances toward the well bore and so completely blocks the interstices and capillary openings that it becomes economically impos sible to produce oil from the well.

Heretofore it' has been found possible to re move the water film from the water-wet sand by depositing a preferential wetting agent in the form of a precipitate on the sand grains which renders them oil-wettable. In this manner the flow of water into the well is resisted by the same force which resists the flow of oil through the water-wet oil producing sand. This procedure is illustrated in Patent No. 2,02,l19, issued to William V. Vietti and Allen D. Garrison, which discloses and claims a method of treating a water-wet oil producing send by depositing a water and oil insoluble precipitate on the sand grains, which precipitate is preferentially wettable by oil. In accordance with the method of the patent an aqueous solution of an alkali metal salt of a sulfonated oil, fat or fatty .acid is introduced into the well and into the producing sand, and is either reacted in situ with calcium and magnesium salts of naturally-occurring grains and is rendered oil-wet by the addition" I of oil thereto. As distinguished from the previous practice the fllm coating is an adsorption film and not a coating formed by chemical or physical precipitation and the wetting compound may or may not be water-insoluble so long as it forms an adsorption film which is oilwettable and crude-oll-lnsoluble. This oil-,wet-

table adsorption film coating is probably caused by the placement of a single molecular layer of the compound upon the face of the sand grains with the formation of a secondary valence bond between the surface of the sand grain and the active portion of the compounds molecule, leaving the inactive portion of the molecule outwardly oriented on the sand face. The outwardlyoriented portion of the molecule possessesa greater amni'ty for petroleum 011 than for id water and therefore facilitates the passage of oil past the filmed sand grain to the exclusion of water.

In accordance with the present invention it has been found that oil-insoluble polyvalent metal salts of low molecular weight fatty acids possess the property of forming an oil-.wettable adsorption film coating upon water-wet sands. These compounds when injected into the oil producing sands adjacent the Wellbore displace the water film around the sand grains of the waterwet sand and form a molecular film over the sand grain, with the organic portion or the molecule thought to be outwardly oriented. Since the films are of molecular thickness the capillary openings between the sand grains are not reduced in size and the normal flow of fluids through these capillaries is not resisted. Among the compounds found .most suitable for the purposes of the invention are the oil-insoluble lead,

as magnesium, mercury and zinc salts of acetic, pro- Opionic and butyric acids and in particular, the

lead salts, such as lead acetate. Preferably, the polyvalent metal salts oflow molecular weight fatty acids, which are resistant to rapid hydrolysis in the presence of water,. are used. These compounds are introduced into the formations in dilute neutral or alkaline solutions ranging in concentration from 1-5% by weight.

. Where the compound is water-soluble an aqueous solution is used, but in the case of the waterinsoluble compounds, such as lead butyrate, an acetone or other organic solvent solution is used. In practical applications to a well the dilute solution of the polyvalent metal salt to be used 50 is either pumped or poured in from the surface, depending upon the normal bottom hole pressure of the well. After the solution has been in contact with the sand for a short time it is driven back into the sand formation by either pumping 55 or otherwise introducing oil into the well bore.

In those cases where the bottom hole pressure is relatively low, oil may be driven into the sand by merely'filling the well bore with oil and permitting it to flow book into the sand. In other cases where the well is flowing under its own pressure it may be necessary to pump the oil-wetting solution and the 011 back under pressure. In all cases the oil is injected under sufllclent pressure to displace the oil-wetting solution and oil-wet the sand grains adjacent the well bore.

Prior to the introduction of the above-mentioned solutions in the well, the producing sand may be pretreated as disclosed and claimed in mycopending application Serial No. 212,972, filed June 10, 1938, by flushing to remove fine clay particles and silt from the interstices and pore space of the'sand. This may be accomplished by introducing a charge of an aqueous alkaline solution of a meta phosphate such as sodium hexametaphosphate, which also may contain a bufler salt or salt mixture and a clay dispersing colloidal agent of the character of alkali metal salts of organic acids, such as tannic acid, gallic acid, and the like. -This flushing treatment may also be modified in accordance with the method of flushing described and claimed in my copending application Serial No. 301,754, filed October 28, 1939, now United States Patent No. 2,246,726, which describes and claims a preliminary flushing of the producing sand with an aqueous alkaline solution containing a clay dispersing agent or calcium sequestering agent, or both, or the combination of either or both with a wetting agent.-

In addition to the flushing treatments specified above, or in lieu thereof, the sand may be pretreated by dehydrating the same to remove water from the pore space, as disclosed'and claimed in my copending application Serial No. 212,974, filed June 10, 1938, now United States Patent No. 2,241,253. This may be accomplished by blowing with a heated gas under pressure, by electrical heaters or heated bodies lowered into the well opposite the producing sand, by a combination of I the electrical heaters or heated bodies with the fiow of gas under pressure, or by'the use of a chemical dehydrating agent. A suitable method of chemically dehydrating the producing sand is that disclosed and claimed in my copending application Serial No. 212,976, filed June 10, 1938, now United States Patent No. 2,248,725, in which the sand is first flushed with oil and then with a mixture of 'oil and an aliphatic ke'tone, such as acetone, and finally,- with a solution of an acid' anhydride, such as acetic anhydride, in oil, preferably containing a small amount of a suitable 2, 1,254, wherein, after the deposition of the oil-wettablefilmupon thesand grains, thecoated oussolution containing 054.0% of either sodium tetraphosphate or hexametaphosphate, and from .2.5% of an emulsifying agent, such as a sulfonated mixture of mineral lubricating oil and benzene, which solution is alkaline to a'pH of about 9 or more, is pumped into the formation surrounding the well screen. This washing solution removes finely-divided clay particles and silt from the pores of the sand, reduces the surface tension of the contact between oil and water and raises the alkalinity of the sand grain surfaces preparatory to the selective wetting treatment. A large volume of oil is then pumped in to force the water of the formation and that introduced in the washing solution. back into the pores of the sand, so as to reduce the pore space water to a minimum in the immediate vicinity of the well bore. After this step a fresh 2-5% aqueous solution of lead acetate is pumped in.

This solution passes through the sand without leaving any materials to block the pores and deposits on the wet sand surface an adsorption film coating of lead acetate. As mentioned previously, other solutions may be used, and it is to be noted that when using solutions of hydrolyzable metal salts the solution must be prepared fresh and pumped in immediately thereafter. The formed film coating is then rendered oil-wet by the addition of a large amount of oil which drives all the previous agents deep into the sand bed and oil-wets the sand grains adjacent the well bore. This may 'be followed by a dehydration step, such as the blowing of the formation with hot gas, air, or oil vapors. The last traces ofwater may thus be replaced by oil, at least in the immediate vicinity of the well bore, to render the sand more permanently oil-wet, and to assist in drying swelled clay and shale fragments. The well is then placed back on production.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit am scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

What I claim is:

1. The method of treating a water-wet oilproducing sand to render the sand more permeable to oil and less permeable to water, which comprises depositing upon the sand grains an oil insoluble film coating of a polyvalent metal salt of a low molecular weight fatty acid and wetting said fllm coating with petroleum oil.

2. The method of claim-1 in which the low molecular weight fatty acid is selected from the group consisting of acetic, propionic and butyric acids.

v decrease the production of water, which comprises injecting into the sand adjacent. the well here a 1-6% solution of an oil insoluble polyvalent metal salt of a low molecular weight fatty sand is further dehydrated by blowing with heated gas under, pressure or with electrical heaters or heated bodies and the like, and then flushing the dehydrated'sand with oil containing a hydrophobic' colloid, such as finely-divided asphalt, tar, acids, graphite and the like.

As a specific example of the method of Op ration according to the present invention, an'aque- 'meable to oil' and less permeable to water, which comprises injecting 'into the oil producing sand 81 01M101! of a metal salt 01a low molecular assaaoe i weight fatty acid selected from the group consisting of the lead, magnesium, zinc, and mercury salts of low rwlecular weight fatty acids.

7. The method of jreating an oil well to render a water-wet producing sand more permeable to oil and less permeable to-water, which comprises injecting into the oil producing sand a solution of alead salt of a low molecular weight fatty acid.

8. The method of treating an oil well to render a water-wet producing sand more permeable to oil and less permeable to water, which comprises injecting into the oil' producing sand an aqueous solution of a water-solublemetal salt of a low molecular weight fatty acid selected from the group consisting of water-soluble lead, magnesium, zinc, and mercury salts of low molecular weight fatty acids.

9. The method of treating an oil well to render a water-wet producing sand more permeable to oil and less permeable to water, which comprises injecting into the oil producing sand an aqueous solution of lead acetate.

ill. The method of treating any oil well to render a water-wet producing sand more permeable to oil and less permeable to water, which comprises washing the producing-sand adjacent the well bore with an alkaline agueous washing solution, forcing through said sand adjacent the well bore petroleum oil to force the water away from the well bore, introducing into the sand a 24% aqueous solution of lead acetate, and then forcing into the sand a petroleumoli to oil-wet the sand adjacent the well bore.

11. The method of treating anoii well to render 9. water-wet producing sand more permeable to oil and less permeable to water, which com-- prises washing the producing sand adjacent the wellbore with an 1 e aqueous washing solution comprising sodium hexametaphosphate and an emulsifying agent, forcing through said sand adjacent the well bore petroleum oil to force the water away from the well bore, introducing into the sand a 2-5% aqueous solution of lead acetate, and then forcing into the sand a petroleum oil to oil-wet the sand adjacent the well bore. 1

12. The method of treating a water-wet oil producing sand to render the sand more permeable to oil and less permeable to water, which comprises dehydrating the sand to remove water from the pore space thereof, depositing upon the sand grains an oil insoluble film coating of a polyvalent metal salt of a low molecular weight fatty acid, and wetting said film coating with petroleum oil.

13. The method of treating an oil well to render a water-wet producing sand more permeable to oil and less permeable to water, which comprises dehydrating the oil producing sand to remove water from the pore space thereof, injecting into the sand a solution of a metal salt of a low molecular weight fatty acid selected from the group consisting of lead, magnesium, zinc, and mercury salts of low molecular weight fatty acids, and then forcing into the sand a petroleum oil to oil-wet the sand adjacent the well bore.

14. The method of treating an oil well to render 9. water-wet producing sand more permeable to oil and less permeable to water, which comprises dehydrating the oil producing sand to remove water from the pore space thereof, injecting into the sand an aqueous solution of lead acetate, and then forcing into the send a petroleum oil to oil-wet the sand adjacent the weilbore.

ALLEN D. G