US2941594A - Method of controlling solids in fluids from wells - Google Patents

Description

June 21, 1960 J, LADD ETAL 2,941,594

METHOD OF CONTROLLING SOLIDS IN FLUIDS FROM WELLS I Filed Oct. 22, 1956 INVENTORS.

- BYWM arrow/5Y5 Byrle J. Ladd and Julous C. Philippi, Houma, La., as-

signors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed on. 22, 1956, Ser. No. 611,375

9 Claims. (Cl. 166-12) The invention relates to methods of treating fluidproducing wells. It more particularly relates to a method of treating wells producing from formations containing, or contiguous to, unconsolidated or incompetent strata and resulting in objectionable detritus in the fluid being produced. it especially relates to a method of preventing the passage of the resulting detritus into. the well.

lnthe production of fiuids such as natural gas, water, brine, and petroleum, producers thereof are frequently confronted. with the presence of detrital' material, e.g., float-sand or marl, which has become. detachedfrom disintegrating reservoir rock. and is carriedinto the well bore by the force of the fluid being produced. The problem is particularly troublesome in petroleum producing wells which produce from incompetent formations. Some of such detached material is carriecl'up with the petroleum and must be removed therefrom by centrifugation or otherwise; Due to the abrasive character of the material, it causes excessive wear on pumping and transfer equip.- ment. An appreciable portion of such detached material accumulates in the lower. portions of the well bore thereby causing loss in efliciency of the well. Such. accumula tionsfrequently cause a shut-down of the well for lack of fluid fi'ow, necessitating a Well-cleaning job. If is. common for wells producing from incompetent formations to require frequent cleaning due to such detrital. accumulations. i

There has long existed a need for. a satisfactory method of overcoming the problems associated with the detrital material which migrates into well bores or is carried therein by the fluids being produced. Numerous attempts have been made to overcome the problems. Among such attempts are underreaming below the tubing to increase the hole size and employing. a limiting choke which re:- duces the rate of flow from the well so that the movement of the flow toward the well bore is greatly reduced. Other methods include the use of a gravel pack or a pebble screen which comprises forms of coarse filter beds andthe ing fine sandtadjacent. to the Well here into. a. more or less monolithic conglomeration. None of these attempts has been satisfactory except in those instances where the amount of detrital material present was small and the control problem therefore not acute. There exists, therefore, a desideratum in the art of providing a method of substantially preventing detrital material, detached from incompetent producing formations, from being carried into the well bore by the fiuid being produced. Accordingly, the principal object of the invention is to fulfill this need. Other objects and advantages of the invention will become apparent as the description thereof proceeds.

The invention is predicated upon the discovery that an elfective fluid permeable barriert'o the passage of detrital particles can be positioned in a well by inserting a liner into the well, substantially concentric with the well casing, for the purpose of retaining in position while hardening, a barrier-forming composition which consists "ice essentially of resin-coated. particulate solids suspended in a carrier liquid.

The invention then comprises inserting into a Well, having a casing, therein andpenetrating a fiuid-bearing formation, a Well liner, positioning the liner to define an annulus with said casing, coating particulate solids with a. settable resin capable of'susp'ension. in a carrier liquid, suspending the thus resin-coated particulate solids in the carrier to form a slurry, and injectingthe thus-formed slurry into the well. The thus-injected slurry is held in position in the annulus by the liner while the resin suspended therein sets in situ to form a rigid fluid-permeable barrier to the passage of detrital particles. The casing may be perforated or unperforated. In the treatment of a well in which the casing is unperforated and the fluid being produced gains access to; the well tubing by passing beneath the lowerend'of the casing, an annulus having. a somewhat irregular outer periphery is formed between the liner and wall ofthewell bore in the formation. The fluid-permeablebarrier is formed in the annulus thus formed in a similar manner to that formed in. the aforementioned annulus formed between the liner and easing.

In carrying out the invention, the liner selected may be either perforated or slotted; it may be plain or blank, i.e., the liner need have no perforations or slots in it; or it may be a fine meshed screen, the openings therein being sufficiently small to prevent passage therethrough of the slurry. A perforated or slotted liner is preferred sinceit may be'left in the well after the resin has set. If a blank liner is used, it may be partially or completely dissolved, after the resin has set, as by use of a solvent chemical, e;g=, a 10 to 25 percent aqueous solution of HCl, or mechanically rendered permeable, as by removing portions or all of it by drilling, before the well is ready for use after treatment. Perforated or slotted liners may be either shop-perforated or perforated after insertion in the well by a knife or shot perforator. Shot-perforated or slotted liners are usually used. The perforations or slots may vary widely in shape and number. The opeuings in the perforations or slots must be sufficiently small to retain the slurry used in treating the well but sufficiently large to permit passage therethrough of the fluid produced by thewell. The slotted liners having elongated slots are preferred to those having perforations which tend to be rectangular or circular in shape. A typical slotted lineris one in which the slots are generally lateral in relation to the liner, i.e. form a series of interrupted horizontal rings running circumferentially around the liner. Although the slots may follow any arrangement or pattern, they are generally between 1 and 3 inches long, between 1 and 2 inches apart laterally, i.e., along the circumferential rings, and from 0.5 to 1.5 inches apart measured longitudinally along the liner. The openings in the'slots are usually from between 0.1 and 0.03 or 0.4 inch wide. The liner may be of iron, aluminum, magnesium, copper or their alloys. A gauge of 0.1 to 1.0 inch is usually used.

The length of the liner is governed by the depth of the pay zone or zones in the well bore which are located in incompetent formations. It is not necessary that the liner extend completely through each of such zones but it should extend sufiici'ently therethrough to retain the mass of resin-coated particles substantially in place While the resin is hardening or setting. The length of the liner may, therefore, be from 4 to 5 feet to several hundred feet. casing. When so placed its inside diameter must be sufiiciently greater than that of the well tubing to allow for its later being run into the well, and its outside diameter must be sufliciently smaller than that of the casing to permit its insertion therein. As an alternative method of practicing the invention, the liner may be placed out- The liner is usually placedinside of the side of the casing to provide an annulus radially exterior of the casing between the casing and the liner. Such placement, however, offers a number of disadvantages and is therefore a less desirable arrangement than the placement of the liner inside of the casing.

The particulate solids to be used in the invention may be selected from various fragmented materials among which are crushed nut shell, e.g., walnut shell, gilsonitc, ground coke, sand, and ground resinous solids, such as. phenol-formaldehyde, furfuryl alcohol-aldehyde" and epoxy resins. They must be insoluble in the liquid resin used to cement the particles together and insoluble in the suspending oil of the slurry. I p Exceptionally coarse and exceptionally fine particles are to be avoided. The range of particle size of the fragmented material is to be controlled so that the difierence between the coarser and finer particles present does not permit packing of the particles in the barrier to such an extent that a monolithic structure of low fluid-permeability is formed. A range of sizes of particles is selected that permits sufficient interstitial space for the passage of the fluid being produced in the well. To obtain the desired particlesize range, the solids to be used are crushed so that a minimum of very coarse and very fine particles are formed and thereafter by two or more screening operations of the crushed solids, a substantial portion of those particles which are very coarse or very fine compared to the average particle size are eliminated. For desirable results, the particles composing a mass of particulate solids to be employed in treating a well according to the invention should be such that not over percent are sufficiently fine to pass through a No. 100 sieve nor over 10 percent sufliciently coarse to be retained on a No. 10 sieve (United States Bureau of Standards Sieve series). Table I below shows the permeability of the various particle-size ranges of test samples of fragmented walnut shells.

. Table I shows that the permeability sharply decreases 4 The phenol-formaldehyde resins are particularly effective because by variations in the formulation of the monomeric mixture, as hereinafter described, setting times may be adjusted to meet various temperature conditions in the well at levels at which the barrier is to be located. This property is highly advantageous because it permits easy handling of the plastic mass of plasticcoated particles prior to and during the injection into the; well and because the period of set may be adjusted to permit adequate time for coating the particles, preparing the suspension in the carrier liquid, and injecting the in the well, as by dissolving, subsequent to injection, a suitable catalyst in a carrier liquid and circulating the liquid, containing the catalyst thus dissolved, in the well.

Slower acting catalysts are usually used when added prior to injection of the slurry whereas a faster acting catalyst may be employed when used after the slurry has been injected.

essary.

as the range in particle size of the test sample widens.

The resin suitable for binding the particulate solids in the practice of the invention is one which is sufiiciently adhesive to coat the solid particles when brought in c011 tact therewith and to bind the coated particles together.

It must not fill the interstices between the particles and 7 thereby seriously impair the fiuid-permeability of the mass thereby formed. It must be sufficiently viscous to remain substantially uniformly dispersed. It must resist being removed by the carrier liquid into which the coated solid articles are sus ended for in'ectin into the anp p 1 g caused to set to a hard strong solid by means of a suitnulus provided therefor in the well. It must also resist being dislodged from the particles during the resin-setting period in the well. The resin must be of a class described as settable, that is, one that sets or hardens either by its merely being reteained in place for a limited time period or one in which the hardening-process is initiated or accelerated by such hardening agents as heat or a chemical catalyst. It must be of a durable nature and resistant to attack by materials normally present in the rock formations or in well-treating agents commonly used.

Resins which may be employed in the invention are liquid-stage polyesters, such as a polymer of a polyhydric alcohol, e.-g., propylene glycol, and a polybasic acid, e.g., adipic or phthalic acid, vinyl-modified polyesters, epoxy resins, melamine-formaldehyde resins, urea-formal- .hyde resins, and phenol-formaldehyde resins.

Examples 1 to 3 are illustrative of the preparation of liquid phenol-formaldehyde resins capable of setting in the earth formation within various ranges of temperatures, as indicated, when suitably catalyzed.

Example I An adhesive resin for use in the temperature range of 200 to 280 F. is prepared as follows: Mix together 1538 pounds of formaldehyde solution (37 percent formalde hyde, balance water), 1179 pounds of phenol, and 35 pounds of 20 B. hydrochloric acid. Heat the mixture to a temperature of F. until it becomes cloudy. This heating usually requires about 15 to 20 minutes. After the cloudy stage is reached, continue heating for an additional 30 minutes. At the end of this heatingperiod, admix 16 pounds of sodium hydroxide into the mixture. As a result, the mixture separates into two liquid phases which. are allowed to stratify. The resulting upper layer is largely water and is discarded. The resulting bottom layer, which has a volume of about 150 gallons, is a thick partially condensed phenol-formaldehyde liquid resin having a viscosity of about 700 to 950 cps. at 80? E, a pH between 4.8 and 5.2, and a density of 9.9 pounds per gallon. This liquid plastic is stable at ordinary temperatures for about 6 to 8 months. During this time, it may be An adhesive resin for use in the temperature range of to 220 F. is prepared as follows:

Mix together 390 pounds of phenol, 506 pounds of formaldehyde solution (37 percent by weight of formaldehyde, balance water) and 50 pounds of a 50 percent solution of sodium hydroxide in water. Hold the mixture at about F. for about 2.5 hours, allowing the phenol and formaldehyde to partially react together. Then mix the so-obtained reaction mass with sufiicient hydrochloric acid to lower the pH to between about 4 and 6. This usually requires about 6.4 gallons of 32 percent, or the equivalent, of aqueous hydrochloric acid solution. As the acid is added, the mixture separates into two phases which are allowed to stratify. The upper layer, which constia ssnso'a An adhesive resin for use in the temperature range of 7 0 to 170 F. is composed of two liquid resins. One of the two liquid resins is prepared by adding 410 pounds of resorcinol to the liquidprepared in Example 2 and mixing until dissolved. A liquid plastic resin is thereby obtained which is an aqueous, partially condensed, phenol-formaldehyde-polyhydroxy benzene resinous liquid. It has a viscosity of about 150 cps. and a density of about 10.2 pounds per gallon. It may be stored at room temperature for as long as 6 to 8 weeks before it becomes ineffective. The other of the two liquid resins is made by mixing together 1116 pounds of cresylic acid, 1068 pounds of an aqueous solution of formaldehyde (37 percent by weight formaldehyde, balance water), 534 pounds of paraformaldehyde, and 67 pounds of a 50 percent aqueous solution of sodium hydroxide. The mixture is heated to a temperature of 125 F. and maintained at this temperature until the mixture becomes clear. This clarification takes place usually in about 30 minutes. To the product soobtained is added 26 gallons of 15 percent hydrochloric acid solution. The addition of the acid brings about the formation of two liquid phases which are allowed to stratify into two layers. The upper layer is largely Water and is discarded. After discarding the upper layer, the remaining lower layer is heated at about 175 F. for from 1 to 1.5 hours so as to'bring the viscosity, as measured at 30 F., to about 200 cps. The resulting liquid plastic has a pH between 3.7 and 4.3, and density of 9.5 pounds per gallon. The amount obtained is about 205 gallons. The two liquid resins thus made are mixed together in equal volumes when they are to be used. The mixture gradually hardens as it ages. However, a hardening or catalyst, e.g. NaOH within the ranges suggested in Tables 2 and 3, is usually used.

The fragmented material, e.g., crushed or ground Waliiut shell, is graded as to size in accordance with the procedure set out hereinbefore, and a suitable liquid resin binder, e.g., a phenol-formaldehyde resin prepared according to Example 1, 2, or 3 above, are mixed to coat the particles with the resin. The coating may be efiected according to any method appropriate to the materials at hand. One efiective method is to tumble the mixed particles and resin in a barrel-type mixer, e.g., a concrete mixer, until the particles are substantially completely coated.

Th amount of liquid resin required is dependent upon the size and nature of the particles used. The required amount can be readily determined by a trial as by mixing various proportions of the particulated material and liquid resin together and noting the appearance of the resulting mass. Particles properly coated exhibit an adhering film of liquid resin which clearly coats the particles but is not of such thickness as to be obviously flowable in respect to the particles. A more certain test is to determine the fluid permeability of the mass after the coated particles are ag lomerated and the resin has set as by placing a 's-am-ple of the coated-particle mass in an open-end tube,

allowing it to set, and measuring the permeability. The

.perrneability drops off sharply when too much resin is used. lnsufiicient resin is indicated by a lack of tensile mixed into the resin as a final 'stepin its preparation or to the mass of resin coated particles after or during the mixing thereof. Suitable hardening. agents for phenolforma'ldehyde resins, such as those in Examples 1 to 3, are alkalis, e.g., sodium hydroxide, potassium carbonate, potassium hydroxide, and amines such as monoisopropylamine, monoethanolamine, triethanolamine, and phenylethanolamine.

Table II shows operable ranges of some hardening agents and mixtures thereof with liquid resins made according to Examples 1 to 3.

TABLE II Fluid Temp, Ounces Liquid Resin Range, Hardening agent of Agent Adhesive F. per

Gallon of Resin Example 3.." 7 to 120 h/Ionoisopropylamine ,0 to 5 Example 3.-.. 120 to 170 NaOH 50% aqueous solution to 3.2 Example 160 to 220 Aqueous solution of 43% 0 to 19 Emmi-5.5% l ZOH. Example 1;: 200 to 250 50% aqueous solution off 1:00 0 to 19 1 Other concentrations, down to or percent but containing equivalenl: amounts of the agent, may be used.

An alternative practice for introducing the hardening agent or catalyst is to coat the particles with the resin without the addition of such agent and insert the thus resin-coated particles into the well free from any added hardening agent and thereafter to treat the agglomerated resin-coated particles in the Well with a hardening agent as by pumping a liquid vehicle containing the agent into the well so as to cause its contacting the mass of coated articles in situ.

A suitable hardening agent to use in this manner is an aqueous solution of a mineral acid, e.g., a 5 to 35 percent by weight aqueous solution of P101 or preferably a 10 to percent HCl solution.

The choice and amount of hardening agent to use will depend upon conditions and circumstances. The state of condensation of the resin and the ambient temperature both at the well head and in the formations in the well to be treated are conditions of importance for consider tion. A circumstance of particular importance, which aifects the choice and amount of agent to be added to the mixture when it is added to the mixture before it is placed in the well, is the anticipation of the period of time to elapse: between addition of the hardening agent and the completion of the steps of making the mixture of the solid particles and resin, suspending the resulting mixture in a suitable carrier liquid, and injecting the thus-suspended mixture in place in the well. Provision must be made for a period sufiiciently long to insure the adhesive property of the resin being substantially unimpaired when the resincoated particles are placed in the annulus provided therefor in the well.

Table III sets forth maximum surface working periods for two different temperatures at the well head and the setting or hardening periods required in the well at three different well temperatures. Three different concentrations of sodium hydroxide in a mixture consistingof fragmented walnut shell of to 40 mesh and a resin prepared according to Example 3- are shown.

TABLE III Fluid Ounces Surface Workof 25% I? ing Time in Shut-iu ".irse in Hours Series No. Solution For Hours allon of Resin F. F. F. ll. 169 F.

Table IV below contains data illustrative of the effect of particle size on theamount of adhesive resin required,

7 the particles being ground walnut shell and the adhesive being the partially condensed phenol-formaldehyde resin of Example 3. As much as about 10 percent by weight of ofif-size particles may be present without serious adverse eifect on the permeability.

The amounts of resin given in Table IV represent generally operativ amounts. Since the amounts of resin recommended are directly related to particle size and comprise a gradual change in amounts, the amounts required for other particle sizes can be ascertained by projecting the relationship of amounts of resin and particle sizes shown in Table IV. Preferred amounts comprise a narrower range than the proportions given. For example, for 20 to 40 mesh particles, 2.4 to 4.0 gallons of resin are a preferred amount to use per 10 pounds of walnut shell.

The liquid phenolic, partially condensed resins which are capable of setting under the temperature conditions in the earth formation to be treated are especially advantageous when used as a coating upon walnut shell because the latter easily becomes wetted by the liquid resin which has substantially no tendency to be washed ofiin the vehicle during injection into the well formations.

Once the resin coating has hardened and the particulated solid is thereby held in a rigid fluid-permeable mass in the earth, earth particles are held back while the fluid produced from the adjacent earth formation passes through the interstices of the cemented mass readily to the well. The permeability obtainable in a mass of particles of ground walnut shell when coated by admixing therewith increasing amounts of phenol-formaldehyd resin are shown in Table V. 7

From the data of Table V, it is manifest that too small a proportion of resin to particulate solid results in a low tensile strength where-as too high a proportion of resin results in low permeability. Therefore it can be seen that the ratio of volume of resin to that of the particles is an important consideration to obtain optimum results but is readily determined by trial when necessary. In Table V, for the combination of the walnut shell and resin used, which produced maximum permeability consistent with high strength was the ratio of resin to nut shell by volume of 7.3 to 50.

Tests have shown that fine sand in suspension in kerosene did not pass through a mass of nut shell particles cemented together by phenol-formaldehyde resin Where the suspension was put under pressure against the mass so that the kerosene passed through. In these tests, the

nut shell was coated with the liquid resin of Example 3 in the proportion of 2.9 gallons per pounds of the particulate shell. The freshly coated particles were agglomerated together and held at 150 F. under petroleum oil for 24 hours until the coating hardened, thereby cementing the particles into a rigid fluid-permeable mass. The petroleum oil was then flushed out of the mass with kerosene and the mass was then dried to remove the kerosene. In one of these tests the nut shell was ground to 20 to 30 mesh; in another it was ground to 20 to 40 mesh. The permeability of each mass so prepared after drying was 500 and 400 millidarcys respectively. When the suspension of sand in'kerosene was brought in contact with the thus-prepared masses and pressure applied to the suspension, the 500 millidarcy mass held back all sand particles coarser than mesh and the 400 millidarcy mass held back all particles coarser than mesh while permitting the kerosene to pass through.

As was stated hereinabove, the hardening agent or catalyst may be withheld from the resin-coated particulate solid mixture and added thereto after the mixture is in position in the well. Withholding the hardening agent or catalyst from the resin-coated particles and bringing it in contact with the resin-coated mixture after it is in position is illustrated by the demonstration set out in the following paragraph in which aqueous HCl was used as a hardening agent for an oil-suspended mass of particulate walnut shell treated with liquid phenol-formaldehyde resin.

Particulate solids consisting of 20 to 40 mesh walnut shell were divided into three portions which are designated A, B, and C, in Table VI. Portions A and B were coated with resin prepared according to Example 3 and portion C was coated with resin prepared according to Example 2 to meet the temperature requirements which were set up. For every 100 gallons of particulate walnut shell, 14.6 gallons of resin were used. The thus-coated shell was then suspended in crude oil to make a pumpable slurry. The slurry was then run into a vertical open-end tube provided with a strainer near the bottom end. The coated particles were thereby retained in the samples of the prepared mass were tested for compres sive strength after aging; the results are tabulated in Table VI.

TABLE VI P.s.i. Compressive Strength Temp. After Aging Portion of hlgss,

' 0.5 Hr. 24 Hr. 12 Br.

Example 4 To illustrate the method of the invention, the following treatment was performed on an oil well. At the time of treatment, the well was closed in, i.e'., was inoperative because sand and other detrital accumulations had lodged in the well bore to the extent that oil could not be pumped or otherwise be made to flow from the well in a sufiicient quantity to justify its operation by an method known to the art.

The depth of the well bore was 6875 feet. The pay zone extended between 6854 and 6862 feet in Miocene sand. The temperature of the Well at the pay zone was P. The casing had a. diameter of 7 inches and g the tubing 2 /2 inches. The casing was perforated with 4 shots per foot through that portion which penetrated the pay zone.

An aluminum shop-slotted cylindrical liner of a diameter'of 4 inches was used. The liner contained in addition to the slots (item 12 of the attached drawing) sixteen inch ports (item 19 of the drawing) arranged in two closely spaced rows extending in a ring-like manner about that portion of the liner which was just above the pay zone of the formation when the liner was positioned in the well.

The slots were cut so that each extended 2 inches circumferentially about the liner. They were about 1.2 inches apart and comprised a series of broken or interrupted rings about the liner which were 11 inch apart longitudinal of the liner, i.e., vertically after the liner was in the well. The slots were aligned longitudinally so that they formed four longitudinal or vertical rows, the rows therefore being about 1.2 inches apart along the liner. The 2-inch long openings in the slots were 0.02 inch wide.

Twenty-two hundred pounds of 20 to 30 mesh particulate walnut shell were placed in a concrete mixer. The mixer was started rotating and 66 gallons of liquid resi prepared according to Example 3, and 20 ounces of 25 percent aqueous sodium hydroxide were added. The mixing was continued minutes to coat the shell particles with a thin film of the resin. The thus-coated shell particles were then mixed with 66 barrels of a viscous refined oil which had a viscosity of 200 cps. The total volume of resin-coated particles and oil was about 3000 gallons. This was a ratio of about 0.73 pound of resin- ,coated particles per gallon of slurry.

The following description of treating a well according to the invention will be best understood by reference to the drawing.

The well penetrating formation 16 to be treated was prepared for treatment by flushing it out with diesel oil 13. Liner 1, having slots as described above, was provided with friction shoe 11 and check valve assembly S at its lower end. Check valve assembly 8 was provided with a threaded recessed slot to engage tubing 2. Tubing 2 was screwed into check valve assembly '8 and liner 1 and tubing 2 thus attached were lowered into the well in substantial alignment with casing 3. There were thus formed two annuli: outer annulus 4 between casing 3 and liner 1 and inner annulus 5 between liner 1 and tubing 2. When liner 1 was in position in the well,

friction shoe 11 rested on the bottom of the well bore and check valve assembly 8 was adjacent to and immediately above friction shoe l1. Checlc valve assembly 8 consisted of an inner and outer part. The inner part, adapted to seat well tubing 2 as stated above, containefd an unidirectional flow control means therein. The outer part thereof was an annular spacer designed to completely close off annulus 5 formed between liner 1 and tubing proper alignment with liner 1 at the upper end of the liner. Check valve assembly 8, therefore was in such position, at the foot of tubing 2 and annulus 5, to direct the slurry from tubing 2 into annulus 4 through outlets 6 but not from annulus 4 into tubing 2 and to prevent passage of slurry from tubing 2 to annulus 5; it also prevented any passage from annulus 4 into annulus 5.

Tubing 2 was then filled with diesel oil 13 and packer 7 set in the well between tubing 2 and casing 3 above the formation to be treated. An additional. three barrels of diesel oil were then added under pressure to force some of the diesel oil out into the formation. Packer 7 was then opened. Four barrels of heavy fuel oil were then added to the well to serve as a buffer between the diesel oil which preceded it and the resin-coated nutshell oil slurry 9 which was to follow it. This relatively high viscosity fuel oil substantially prevented any shell which might drop out of the slurry from falling into the oil below and possibly continuing down to cause bridging at the bottom of the well.

Transfer of the above prepared slurry 9 into tubing 2 by pumping was started. As the pumping continued, shell slurry 9 completely displaced the diesel oil 13 from tubing 2, forcing it out through outlets 6 into the lower end of annulus Packer 7 being open, the necessary displacement of diesel oil from annulus 4, to accommodate diesel oil entering from tubing 2, was provided for by diesel oil passing up and around open packer 7 from annulus 4. By calculations based upon the capacity of tubing 2 and measurement of slurry 9 pumped into the tubing the amount of slurry necessary to fill tubing 2 was determined, pumping was stopped when this amount of slurry had been pumped and packer 7 was again set.

Pumping of slurry 9 was resumed, some of it thereby being forced out through outlets 6 into annulus 4 where it in turn forced the diesel oil 13 remaining therein out through perforations 14 in the casing 3 and back into the formation. Slurry was prevented from entering annulus 5 because of the spacer arrangement in check valve assembly 8. Some of slurry 9 passed out through perforations 14- and into the formation adjacent to the well bore as shown in the drawing.

After fifty-three barrels of slurry were pumped into the well, pumping was stopped, packer 7 opened and tubing 2 disengaged from liner 1 and raised fifty-two feet to a point just above ports 10 in liner 1 which were near its top and located a few feet above formation 16, as shown in Fig. 2. As tubing 2 was raised, since packer 7 was open, oil from the formation together with some of diesel oil 13 filled the entire space within liner 1 below ports 10. The packer was reset and. the pumping of the shell slurry was resumed. The slurry was largely diverted out through ports 10, due to the presence of the oil below ports 10, and into annulus 4 between the casing and the liner. It continued to pass out through ports 10 and into annulus 4, thereby continuing to fill annulus 4 from the top as shown in Fig. 2. After twelve more barrels, a total of sixty-five barrels of slurry 9 had been pumped into the well, operations indicated that annulus 4 was completely filled. Injection of slurry was stopped and packer 7 opened.

The tubing was then lowered so that its lower end was positioned a short distance above valve assembly 8 near the bottom of the well as shown in Fig. 3. Tubing 2 was now in a position to permit passage of slurry under its lowest end from annulus 5 into tubing 2, in the manner explained in the next following paragraph. This arrangernent permitted a reversal of the direction of flow in tubing 2. Fluids could therefore now be pumped down annulus 5 and out tubing 2. Valve assembly 8 prevented passage from annulus 4 into either annulus 5 or tubing 2.

Packer 7 was continued open thus providing passage through the annular space between tubing 2 and casing 3 above the upper end of liner 1. Crude oil 17 as a chaser oil was pumped into this space. The chaser oil passed down the space, entered annulus 5' by way of ports 10, and proceeded down annulus 5 forcing the oil therein, together with any residual slurry in annulus 5, into tubing 2 through the clearance at the bottom of the tubing. This oil in turn displaced upwardly the residual oil and any residual slurry in tubing 2. Substantially all residual oil containing any slurry which had remained in annulus 5 and tubing 2 was thus removed by the reversed direction of flow imparted to the flushing or chaser crude 16.

11 The settable resin in slurry 9 was thereby left to set in situ in annulus 4 and portions of the formation 16 adjacent perforations 14.

The well was shut in for twelve hours to cause the resinous mass to set into a fluid-permeable barrier.

After the shut-in period, the well was put back in production. After treatment it produced 120 barrels per day of crude oil, substantially free from suspended detritus.

The fluid-permeable barrier thus formed acted as an effective filter to remove detrital material from the oil in the formation as it passed intothe well bore.

Reference to Example 4 shows the high degree of control of the detrital material which was attained by thus positioning the fluid-permeable barrier in the well bore according to the method of the invention.

'Modiflcations of the treatment set out in detail in Example 4 may be employed within the scope of the invention. Excellent results may be obtained by injecting the resin-coated shell slurry entirely through the check valve at the lower end of the tubing and hence filling the annular space about the well bore entirely from the bottom. Forming the fluid-permeable barrier in two 'stagesrfirst, by building it up from the bottom and second, completing the forming of the barrier from the top according to the example is merely an optional safeguard tojimpart added assurance of having obtained a fully formed barrier.

Various resin compositions may be employed dependent upon the conditions. Oils of different viscosities and different API gravities may be used in preparing the slurry. A liner without slots or perforations may be used which may be removed by dissolution with an acid of suitable strength. As an alternative method to remov ing the liner by chemical action, all or portions of the liner may be removed mechanically as by drilling with an appropriate bit operated by conventional well-drilling apparatus.

Having thus described the invention, what is claimed and desired to be protected by Letters Patent is:

1. The method of forming a fluid-permeable barrier to the passage of detrital material from a fluid-bearing earth formation into a well penetrating said formation, said well having a casing therein which extends at least a part of the distance to the bottom of the well, which comprises: inserting into the well a string of tubing and a substantially cylindrical screen liner exterior of and substantially concentric with the tubing to form an inner annulus with said tubing and an outer annulus with said casing, forcing into said outer annulus, via said string of pension in a hydrocarbon carrier liquid of particulate organic solid material of such size that not over 10 percent will pass through a number 100 standard screen and not over 10 percent will be retained on a number 10 standard screen coated with a settable resin in suificient amount to form a fluid-permeable unitary mass of such coated particulate material when thus forced into said annulus, said liquid being inert to said particulate material and resin, until said outer annulus is substantially filled; raising the tubing sufficiently to permit passage of slurry around the lower end thereof; reversing the direction of flow in said tubing; pumping a chaser oil down said inner annulus to flush out the inner annulus and tubing; and causing said settable resin to set in situ.

2. The method according to claim 1 wherein the particulate solid'material is ground nut shell.

3. The method according to claim 2 wherein the nut shell is walnut shell.

4. The method according to claim 1 wherein the carrier liquid is an oil derived from petroleum.

5. The method according to claim 1 wherein said so table resin is apartially condensed product of phenol and an aldehyde.

6. The method according to claim 1 wherein the rate of setting of said settable resin in situ is accelerated by incorporating into the resin a hardening agent prior to its injection into the well.

7. The method according to claim 1 wherein the rate of setting of 'said settable resin is accelerated by contacting said resin in situ with a liquid hardening agent.

8. The method according to claim 7 wherein said hardening agent is a 5 to 25 weight percent aqueous solution of HCl.

9. The method of forming a fluid-permeable barrier to the passage of detrital material from a fluid-bearing earth formation into a well penetrating said formation, said well having a casing therein which comprises: inserting inside of the casing a string of tubing and a substantially cylindrical liner exterior of and substantially concentric with the tubing to form an inner annulus with the tubing and an outer annulus with the casing, said liner having a fluid-flow control means secured to the lower end thereof and a series of openings near the upper end thereof for directing fluids from the tubing into the said outer annulus; forcing into the tubing a slurry consisting essentially of a substantially homogeneous suspension in a hydrocarbon carrier liquid of particulate organic solid material of such size that not over 10 percent will pass through a number standard screen and not over 10 percent will be retained on a number 10 standard screen coated with a settable resin in suflicient amount to form a coating over said particles of a sufficient thickness to form a unitary mass of said particles and resin when set but not of a thickness sufiicient to completely fill the interstices between the particles, said resin-coated particulate solid material being insoluble in the carrier liquid and in the fluid of the formation; forcing the slurry out through said fluid control means into said outer annulus at a point near the bottom thereof to partially fill the outer annulus from the bottom upward; raising the tubing to a point above the series of openings in said liner; forcing the slurry out through said series of openings into the outer annulus to complete the filling thereof from the top of said outer annulus downward; lowering the tubing to a point near the bottom of the well to allow for passage of slurry below its lower end; reversing the direction 'of flow in the tubing; pumping a chaser oil down said inner annulus to flush out the inner annulus and tubing; causing said settable resin to set in situ in the outer annulus; and thereafter perforating said liner to render it permeable to fluids.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,941.594 June 21 1960 Byrle J. Ladd et al.

It is. hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, line 1, and in the heading to the printed specification line 7, name of co-inventor, for "Julous C. Philippi", each occurrence read Julius C. Philippi column 2, line 54, for "0.1 and 0.03 or 0.4" read 0.01 and 0.03 or 0.04 column 3, line 63, for "reteained" read retained Signed and sealed this 20th day of December 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

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