US2143991A - Method of shutting off water in oil wells - Google Patents

Description

Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE.

METHOD OF SHU'ITING OFF WATER IN OIL WELLS No Drawing. Application November 2'7, 1934,

Serial No. 755,060

2 Claims.

This invention relates to methods of shutting off water in oil wells; and it comprises a method of differentially shutting off water in an oil well penetrating oil and brine formations which deliver 5 into the well, wherein a solution of a water-soluble soap of the polycyclic naphthenate type is injectecl into the well and surrounding formations under pressure, the well brines usually being forced back into their formations before the soap l0 injection step, with fresh water injected into the well and formations under pressure, the soap being of such character is to interact with the dissolved salts in the formation brine to form a water insoluble but oil soluble plastic deposit in the brine formation at points remote from the well face; all as more fully hereinafter set forth and as claimed.

Oil wells often penetrate water bearing formations as well as oil bearing formations, the two in many cases being closely adjacent. Well waters in most cases are hard. They contain dissolved calcium and magnesium salts including soluble carbonates and chlorids and usually a considerable proportion of common salt. The

term brine as used herein refers to waters containing any of these compounds. It is a desideratum in the oil production art to shut off flow of water or brine into the well without substantially affecting the oil flow.

The present invention relates to a method of differentially shutting off water from such wells without hindering the oil flow. According to the invention the well brines are usually forced back into their formation under pressure and then there is injected into the well and surrounding formations an aqueous solution of a suitable soap; a soap of the polycyclic naphthenate type. The solution penertates readily into the water formation forcing back the local brines, and to a 1 less extent into the oil formation; less because of the incompatibility of water and oil. During the pause when pumping ceases but before the pressure is released, the solution and the local waters mingle more or less, causing a precipitation and producing plugging solids not removed with a release of pressure. On contact with the brine constituents the soap yields a highly water insoluble plastic deposit. The nature of the deposit depends on the constitution of the particular 0 brine in the well. If the dissolved salts are predominantly calcium compounds the deposit formed is mostly water insoluble calcium soap. If the well water is mainly a salt brine, the soap is largely salted out as an insoluble curdy mass. In all cases the deposit is substantially insoluble in water but has considerable solubility or dispersibility, in oil, which allows the oil formations to clear themselves of any deposit upon resuming production. Since the solution penetrates more readily into the water formation than into the 5 oil formation the temporary clogging of the oil formation is minimized. As stated, I regard soaps of the polycyclic naphthenate type as being most useful for my purposes, as the calcium and magnesium naphthenates formed in situ or the 10 naphthenate soap as salted out in the presence of salt brine are much more soluble in 011 than common soaps. Sodium polycyclic napthenate is useful and is available as a by-product in petroleum refineries; from refinery soda sludge. 1

Advantageously, before the injection of the soap solution, fresh water is introduced into the well under pressure to force the brines back into their formation. This prevents deposition of the pre cipitate at the well face, and insures deposition '20 far in the water formation, remote from the Well. This is where plugging is most effective. The fresh water also forces oil back into the oil formation, but to a less extent, owing to the incompatibility of water and oil and to the relatively 25 high viscosity of the oil. The soap solution can now be injected and forced far back into the water formation before precipitation begins. On releasing the pressure, diffusion and deposition occur in the Water formation at points remote 30 from the well face.

In a specific example of the invention as applied to shutting off water in an oil well having a stratum adjacent the oil producing stratum and charged with a brine containing calcium or mag- 35 nesium salts, the contents of the well are flushed out with fresh water under a pressure sufficient to force the fresh water into the producing formations and thus to force Well waters back into their formations, 200 pounds sodium naphthenate of 40 ordinary commercial grade are dissolved in 10,000 pounds water and the batch is injected into the well under high pressure to force the solution as far back into the strata as possible. Presa sure is maintained for a while. Upon releasing pressure and resuming production it is found that the water flow is substantially reduced while the oil flow is not affected permanently. The calcium and magnesium naphthenates formed in situ remain in the interstices of the water formation a long time.

The soap solutions are relatively mobile, and the interaction with the brine constituents is by no means instantaneous. Hence the soap can be u forced a considerable distance back into the formations before the deposit formed prevents further injection. This insures effective sealing.

What I claim is: l. A method of shutting ofi water in brinebearing formations adjacent oil wells, which comprises injecting into the formations in liquid form a water-soluble soap of the polycyclic naphthenate type, the calcium and magnesium derivatives of which are soluble in oil, and causing the soap to mingle with the brine in the brine-bearing formations, so as to form insoluble sealing deposits in the brine-bearing formations.

2. A method of shutting off water in brine-- tions.

ALBERT G. LOOMIS.