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Publication numberUS3302734 A
Publication typeGrant
Publication dateFeb 7, 1967
Filing dateJul 1, 1963
Priority dateJul 1, 1963
Publication numberUS 3302734 A, US 3302734A, US-A-3302734, US3302734 A, US3302734A
InventorsMedadors Victor G
Original AssigneeExxon Production Research Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of sealing a permeable prous medium
US 3302734 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 3,302,734 METHOD OF SEALING A PERMEABLE POROUS MEDIUM Victor G. Meadors, Tulsa, Okla., assignor, by mesne assignments, to Esso Production Research Company, a

corporation of Delaware No Drawing. Filed July 1, 1963, Ser. No. 292,108

8 Claims. (Cl. 175-59) The present invention is generally concerned with the sampling of underground formations. The invention particularly relates to a method for obtaining samples of subterranean strata from wellbores which have been drilled into the earths crust. It is especially directed to a method for obtaining samples of essentially unaltered fluid content by a rotary core drilling technique which involves the use ofa non-invading coring fluid to seal the surfaces of the core samples essentially as drilled.

The stock-tank volume of petroleum contained in a porous underground reservoir is normally calculated in terms of the reservoir volume, the formation volume factor, the average reservoir porosity and the average oil saturation within the pore volume. In reservoirs wherein a number of development wells have been drilled, the reservoir volume and the formation volume factor can usually be determined with reasonable accuracy by comparing structural maps and by measuring the gravity, temperature, pressure and gas content of the oil under reservoir conditions. The average porosity of the reservoir is generally determined by analyzing cores recovered from a number of development wells. Experience has demonstrated, however, that volumetric oil content in the cores as determined from core analysis is usually not an accurate indication of the actual quantity of oil present in a reservoir.

Reliable values for volumetric oil content, together with the other data, are extremely desirable to forecast the productive life of oil and gas reservoirs, to select the primary recovery techniques most suitable for particular reservoirs, and to assess the susceptibility of such reservoirs to later secondary and tertiary recovery processes. It is a principal object of the invention to obtain samples from a reservoir, the analysis of which will provide reliable values for volumetric oil content.

Conventional core drilling systems include an annular bit and core barrel which are rotated from the earths surface by means of a rotary drill string. A coring fluid is circulated downwardly through passages in the drill string, barrel, and bit in order to maintain pressure on the formation and thus prevent the escape of fluids contained therein. Cuttings produced by the bit are entrained in the coring fluid and returned to the surface through the annulus surrounding the drill string. As the bit cuts away the formation the central core which remains is encased in the barrel. The core barrel is provided with means for breaking off the core once the barrel has been filled. Pressure core barrels which can be sealed against changes in pressure are also used. After the core has been cut the drill string is withdrawn from the borehole and the core recovered therefrom.

Studies have shown that the pressure maintained at the bottom of a borehole during a coring operation has a profound effect on the fluid content of the cores subse- "ice quently recovered. If this pressure: is less than the formation pressure,.fluids contained in the formation will tend to flow out of the core into the borehole until equilibrium is established. If on the other hand the bottom hole pressure exceeds the formation pressure, the coring fluid will tend to flow into the interstices of the formation and displace any oil, gas or water contained therein. In either case the result is a change in the fluid content of the core such that subsequent measurements of the amount of fluids present will not accurately reflect the original fluid content of the cored formation. Since this change in fluid content occurs continuously as the core is cut, the use of a pressure core barrel does not prevent it.

Several methods for avoiding the difficulty outlined above have been proposed in the past. The most obvious of these involves carrying out coring operations without any pressure differential between the coring fluid and the formation. This is impractical, if not impossible, because the formation pressure cannot be conveniently measured during core drilling, and moreover, because the coring fluid pressure cannot be controlled with suflicient accuracy.

The use of coring fluids which will not invade the formation under pressures well in excess of the formation pressure has been suggested, but efforts to develop a satisfactory non-invading fluid have not been entirely successful. Mercury, molten metal and other materials advocated in the past all invade the formation to an appreciable extent and hence cause changes in the fluid content. In addition the materials proposed for this purpose have generally been costly and diificult to use and in many cases require highly specialized core bits and core barrels. Other systems including the use of tracers which permit determination of the extent to which core invasion has occurred, and systems for freezing the core have been proposed but have not been found to be generally eflective.

The most promising of the non-invading coring fluids which have been developed heretofore are the polymeric elastomer latices. These materials are aqueous colloidal dispersions. of polymeric elastomers, including natural and synthetic rubber latices.

It has now been found that aqueous dispersions or suspensions of finely divided reclaimed rubber are unexpectedly superior to the natural and synthetic rubber latices, in their ability to seal a permeable porous medium. Specifically, a field-scale rotary coring operation in which a reclaimed rubber dispersion is used as the coring fluid has been found capable of recovering a core sample in which the original fluids content is altered by less than 3% by volume, even when the operation is conducted with as much as 500 psi. pressure differential between the coring fluid and the fluids of the formation being cored.

- Reclaimed rubber is a staple item of commerce, produced by any one of various processes, each of which involves the application of heat and chemical agents to Waste vulcanized rubber, whereby a substantial devulcanization or-regeneration of the rubber to a plastic state is achieved. It may then be processed, compounded, and again vulcanized, similarly as is true of new rubber.

The reclaiming process, from a chemical viewpoint, is

not an exact reversal of the reactions which occur during the vulcanization of natural rubber or synthetic rubber; hence, the term devulcanization has been criticized as misleading and inaccurate. However, the term persists in the literature and is considered to be a valid description of the reclaiming process, inasmuch as a reversal of physical properties does occur. That is, vulcanized rubber is characterized by elasticity and a resistance to compression, stretching and swelling, whereas the devulcanized product is restored to a state of plasticity, more nearly like that of unvulcanized new rubber.

Nevertheless, reclaimed rubber has many unique properties which distinguish it from new rubber. For example, in the processing of a rubber compound, the presence of reclaim in the recipe enhances working properties in all primary stages. Mixing times have been halved and calender speeds doubled. Calender temperatures become less critical, and the gauge of a calendered sheet can be increased without blistering. The uncured stock possesses better dimensional stability and is less susceptible to overmilling. Friction and skim-coating operations are expedited.

Reclaim stocks possess a high rate of cure. They often exhibit improved moulding properties. They possess low thermoplasticity and are less affected by continuous millmg.

There are many types and grades of reclaimed rubber. The most abundant source of reclaimed rubber is old tires, including passenger car and truck tires. Reclaim types produced from tires include the whole tire reclaim, the tire tread reclaim, and the tire carcass reclaim. There is also a red inner tube reclaim and a black inner tube reclaim.

Other types include the mechanical reclaim, the footwear reclaim, the butyl reclaim, the neoprene reclaim and the nitrile reclaim, as well as several others.

In its broadest scope, the present invention includes the use of aqueous dispersions of any of the above types of reclaimed rubber. It also includes the use of mixtures of two or more reclaim types, and mixtures of one or more reclaim types with one or more of the natural and synthetic elastomer latices. In the latter case, however, it is preferred that the mixture contain a major proportion of reclaimed rubber.

Suitable reclaimed rubber dispersions for use in accordance with the invention are readily .available commercially. For example, there is the Loxi-te series of the Firestone Tire and Rubber Co., and the Dispersite series of the Us. Rubber Co. Reclaim dispersions are prepared by first mechanically milling or grinding the reclaimed rubber until its consistency becomes suitably plastic for dispersing water therein. An emulsifying agent is then blended into the rubber, after which water is slowly added. Once the correct amount of water has been added, a change of phase takes place, whereby the water becomes the continuous phase, and the rubber becomes the discontinuous, or dispersed phase.

Dispersions containing from about 20% to about 75% reclaim by weight are generally suitable for purposes of the invention. Those containing from about 35% to about 70% are preferred.

Reclaim rubber dispersions are chanacterized by a relatively wide distribution of particle sizes, ranging from as small as 0.1 micron in diameter to as large as 35 microns. The average particle size of commercially available reclaim dispersions is subject, however, to relatively little variation since as a practical matter, the particle size is determined by such factors as the amount and type of emulsifier used, and the point at which inversion from a water-in-oil type to an oil-in-water type of dispersion occurs.

Core drilling operations utilizing the coring fluid of the invention may be carried out with conventional apparatus familiar to those skilled in the art. A variety of commercially available core bits and core barrels may be used. The coring fluid is circulated down the drill string through channels in the core barrel and bit so that it emerges adjacent the cutting surfaces of the bit. The fluid contacts the core surfaces as the surrounding rock is cut away and continuously forms a film on the surface which is impermeable to oil, gas and water, thus preventing any significant alteration of the original fluid saturations in the core. Once a coated core of suflicient length has been cut, it is separated from the formation, and lifted to the surface inside the core barrel.

The nature and objects of the invention can be more fully understood by reference to the following experimental work, conducted to demonstrate the effectiveness of the invention.

Static invasion tests were conducted to compare the sea-ling ability of a reclaimed rubber dispersion with the corresponding eflectiveness of natural and synthetic rubber latices. Berea sandstone cores of about 1.5 inches in diameter and about one inch in length, having a porosity of about 20% and a permeability ranging from 200 to 300 millidarcies, were used in testing the fluids. Each core was first saturated with a mixture of oil and brine, to simulate field conditions, and then mounted in a conventional core holder. As summarized in Table I, the cores were then exposed to the test fluids, under a driving force of p.s.i.,differential pressure.

TABLE I Filtrate invasion rate, milliliters per minute Coring Fluid: after five minutes exposure 2 parts Nitrex 2620, 1 part natural latex, 4.4%

silica flour 0.02

2 parts Naugatex 2001, 1 part natural latex,

4.4% silica flour 0.02 50/50 (vol.) Dispersite 1685-natural latex 0.01 Dispersite 1685 0.01

Dispersite 1685 is a trademark of Naugatuck Chemical Company, a division of the US. Rubber Co., Naugatuck, Connecticut. The product is a rubber-in-water dispersion prepared from first quality whole tire reclaim, and having a total solids content of about 60 weight percent.

Nitrex 2620 is a latex prepared by the emulsion polymerization of 65 weight percent butadiene and 35 Weight percent acrylonitrile in the presence of a persulfate catalyst and about 8 weight percent of potassium rosin soap emulsifier. It has a 40 weight percent solids content and an average particle diameter of 0.07 microns.

Naugatex 2001 is an SBR latex the elastomer of which contains 46 percent bound styrene. The latex has a total solids content of 42 percent by weight, and a particle size of about 0.10 micron.

In another series of tests, cores were drilled from blocks of porous sandstone using conventional rotary core-drilling equipment. The sandstone blocks measured 12 inches square by 24 inches deep, and were prepared for the tests by replacing the natural fluids contained therein with carefully measured amounts of oil and brine. A typical block contained 60 percent oil and 40 percent brine. The oil employed was a 12 centipoise white paraflinic hydrocarbon oil. The brine contained 2,500 parts per million of calcium ion, 1,000 parts per million magnesium ion, and 26,000 parts per million sodium ion, present as the chloride salts, which is typical of oil fie-ld brines.

The sandstone block, the core bit and the core barrel were encased in a pressure-tight chamber to permit the simulation of high formation pressures. The coring fluids were circulated from a reservoir through the drill pipe, core barrel, and core bit by a high pressure pump. The cuttings were lifted by the fluids through the annulus surrounding the drill string, after which the fluids were freed of cuttings and recirculated. The coring fluids were circulated at a pressure differential of about 75 p.s.i. in excess of that maintained within the sandstone block. The circulation rate was about 38 gallons per minute. This particular equipment and these conditions were selected because earlier tests had shown that the results obtained were comparable to those obtained in actual field operations. The results are summarized in the following table.

TABLE II Goring Fluid 50/50 (vol) 50/50 (vol.) 2 Parts Nitrex Dispersite Dispersite 26:20, 1 Part 1G85Natural 1685Natural Natural Rubber Latex Rubber Latex Rubber Latex Total Solids, percent- 64. 8 64. 8 51 Bit, r.p.m 30 30 30 Bit Weight lbs 10, 000 10,000 10,000 Inches eore(l. l5. 7 16. 6 16.8 Goring Time, min 6. 5 5. 3 5. 6 S0 in Rock, percent PV 59. 4 45. 2 62. 2 So in Core, percent PV 52.0 35. 4 46. 4 Difference, percent The data summarized in Table II further demonstrate the superiority of reclaimed rubber dispersions over the natural and synthetic rubber latices.

Additional tests were conducted, in which a core sample, or series of core samples, was drilled with conventional field-scale rotary core-drilling equipment from an octagonal block of Berea sandstone measuring four feet in length and ten inches between parallel sides. Each block was first cemented inside a length of 11% inch diameter steel casing which was equipped with suitable fittings to :permit the simulation of high formation pressures while drilling. The results are summarized in Table III.

TABLE III [Goring fluidDispersite D-735] Dispersite D-735 is an aqueous reclaimed rubber dispersion containing -65% by weight of oil-extended first quality whole tire reclaim.

These data further indicate the superiority of reclaimed rubber dispersions as coring fluids in the recovery of core samples of substantially unaltered fluids content.

What is claimed is:

1. A process for the recovery of core samples from a borehole in the earth which comprises advancing a rotary core-bit into the earth at the bottom of said borehole, while circulating downhole a fluid comprising a dispersion of finely divided reclaimed rubber in water, whereby the sample recovered are sealed substantitally as cut, thereby capturing the original fluids contained therein.

2. A process as defined by claim 1 wherein the dispersed phase of said dispersion comprises first quality whole tire reclaim.

3. A process as defined by claim 1 wherein the rubber content of said dispersion is 35 to by weight.

4. A process as defined by claim 1 wherein the dispersed phase of said dispersion comprises reclaim rubber plus natural latex, and the combined rubber content thereof is 35 to 70% by Weight.

5. In the recovery of core samples from a borehole in the earth by rotary-core-drilling wherein a sealing fluid is circulated downhole, the improvement which comprises circulating as said fluid a composition comprising a dispersion of finely divided reclaimed rubber in water.

6. A process as defined by claim 5 wherein said dispersion contains first quality whole tire reclaim.

7. A process as defined by claim 5 wherein the dispersed phase of said composition consists essentially of first quality whole tire reclaim.

8. A process as defined by claim 5 wherein the rubber content of said dispersion is in the range of 35% to 70% by weight.

References Cited by the Examiner UNITED STATES PATENTS 3/1964 Ga'llus 59 11/1964 Gallus 175-59

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3123158 *Mar 3, 1964 sealing porous sukfaces
US3158209 *Jul 30, 1962Nov 24, 1964Jersey Prod Res CoMethod of sampling underground formations
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5546798 *May 12, 1995Aug 20, 1996Baker Hughes IncorporatedMethod and composition for preserving core sample integrity using a water soluble encapsulating material
US6283228Dec 15, 2000Sep 4, 2001Baker Hughes IncorporatedMethod for preserving core sample integrity
US8757293Jan 24, 2008Jun 24, 2014J. I. Livingstone Enterprises Ltd.Air hammer coring apparatus and method
US20100084193 *Jan 24, 2008Apr 8, 2010J.I. Livingstone Enterprises Ltd.Air hammer coring apparatus and method
U.S. Classification175/59
International ClassificationE21B25/08, E21B25/00
Cooperative ClassificationE21B25/08
European ClassificationE21B25/08