WO1993018111A1

WO1993018111A1 - Materials incorporating cellulose fibres, methods for their production and products incorporating such materials

Info

Publication number: WO1993018111A1
Application number: PCT/GB1993/000491
Authority: WO
Inventors: Paul Douglas Maxfield Gullett; Philip Frederick Head
Original assignee: Stirling Design International Limited
Priority date: 1992-03-09
Filing date: 1993-03-09
Publication date: 1993-09-16
Also published as: GB9205085D0

Abstract

Pulp residue waste is treated by reducing the water content below 7 % and is then milled in a ball mill and classified to remove particles of the inorganic filler greater than 1000 microns. When this material has a particle of the inorganic filler size below 20 microns, it can be used as a filler in plastics materials. When the particle size of the inorganic filler is between 50 microns and 1000 microns, it can be used as a lost circulation material in oil wells, where it gives excellent control of seepage or loss.

Description

MATERIALS INCORPORATING CELLULOSE FIBRES. METHODS FOR THEIR PRODUCTION AND PRODUCTS INCORPORATING SUCH MATERIALS

The invention relates to materials including cellulose fibres, methods for producing such materials and products incorporating such materials. In particular, the cellulose fibres to which the invention is directed are those incorporated in the waste from paper mills.

Pulp residue waste from paper mills is derived from processing used paper, used paper and virgin cellulose, or virgin cellulose and it is the material remaining after the pulp has been removed for making into new paper. It is produced in the United Kingdom in substantial quantities - up to 500,000- tons per annum. The waste contains inorganic fillers, which are largely kaolin clays and calcium carbonate, as well as cellulose fibres and some latex. In addition, where the used paper includes oil bound inks (such as colour printed paper), the waste will also include organophilic bentonite. As a result of processing, the cellulose fibres are highly fibrillated and it is believed that the clay particles are trapped in the fibres, giving a particularly homogeneous composition.

The principal solid components of the waste are the inorganic fillers and the cellulose fibres and these are held in water. Typical pulp residue waste may be 70% water and 30% dry mattex by weight. Of the dry matter, the inorganic fillers may represent 27%-70% by weight and are typically 30% by weight with the cellulose fibres being not less than 30% by weight.

There have been a number of proposals for utilizing such waste to make useful materials. For example, EP-A1-0169946 describes mixing the waste with a surfactant and then de-watering the waste and drying the semi-dry mass by means of a screw, thus granulating the material. Such a granular . material can be used for liquid or shock absorption.

U-A-4721059 discloses the treatment of pulp residue waste by adjusting the moisture content of the waste until it is shreddable, reducing the fibre size of the waste, conglomerating the waste into granules which mimic the appearance of naturally occurring clay and then drying the granules. The disclosed use of such granules is as a filler for a cat box.

US-A-4356060 discloses the treatment of pulp residue waste comprising heating the waste to remove substantially all the water and to convert the waste into lipophilic or hydrophobic granules. Next the product is milled in a hammer mill, and forced out of the mill through a mesh screen. The resultant material is in the form of particulate soft fluffy aggregations which, on pressing, form loosely matted masses or can be compressed into batts.

PCT Application GB90/00475 discloses the treatment of pulp residue waste by de-watering the waste and then drying the resulting product to a residual water content of up to 1% by weight. The product can then be pelletized or otherwise comminuted. This produces a granular product that can be used as a filler for plastics material.

The materials produced by these disclosures may be useful for the purposes indicated but other structures are possible which have different ^• advantageous' properties. For example, at least some of the materials formed as described in the documents referred to above may not be able to be readily dispersed in a liquid and so cannot be used to modify the properties of liquids.

According to a first aspect of the invention, there is provided a particulate material having a dry matter content of up to 70% by weight of inorganic fillers and not less than 30% by weight of cellulose fibres, and having a free water content of not more than 70%, the inorganic filler being in particulate form and having a particle size of not greater than 1000 microns.

According to a second aspect of the invention, there is provided a method of producing a particulate material comprising drying a mixture of dry matter and water to⁰a free water content of less than 7% by weight, the dry matter including up to 70% by weight of inorganic fillers and not less than 30% by weight of cellulose fibres and then reducing the inorganic fillers to particulate form with a particle size of less than 1000 microns.

The material of the first aspect of the invention and the material produced by the second aspect of the invention have a variety of uses. For example, they can be used as fillers in plastics materials,- as a modifier in cements, in inks, they can be used in paints and as filter materials, replacing diatamaceous earth, or in a fluid transport medium.

They can also be used in oil wells to modify the properties of drilling muds. An important function of a drilling mud is the efficient removal of matter cut by a drill bit and the transport of such matter to the surface. The viscosity of the drilling mud must thus be such as to perform such a function and the mud must be thixotropic so that when circulation ceases cut material is held in suspension in the mud and does not fall to the bottom of the hole.

These and other known requirements of drilling muds require specific rheological properties for drilling muds. It is important that these .properties are not altered during drilling, since such alteration can have disadvantageous consequences.

A problem that occurs in the drilling of oil wells is the presence of formations that cause lost circulation of the drilling mud. This can arise because of fractured or cracked formations or because of porous formations such as sand. They can result in either partial or catastrophic loss of drilling mud, or in the reduction of the liquid content of the mud and a consequent disadvantageous increase in the viscosity of the drilling mud.

It is known to add to the mud various lost circulation materials whose stated purpose is to seal the formations and so reduce or prevent the loss of drilling mud or drilling mud liquid. For example, US-A-3,208,523 discloses the use of magnesia powders and filter aid powders for this purpose. US-A-3,574,099 discloses the use of asbestos fibres. US-A-4,853,465 discloses the use of organophillic polyphenolic materials. US-A-4,956,104 and 4,863,950 disclose the use of organophillic polymers including an anionic or cationic water soluble polymer and one or more phosphatides. US-A-4,404,107 discloses^' the use of water wettable cotton reacted with hydrochloric acid. US-A-4,737,295 discloses the use of polyphenolic materials and one or more phosphatides.

It has also been proposed to use cellulose fibres for this purpose. US-A-4,428,843 discloses the use of raw untreated cotton linters, peat fibres and bagasses. US-A-4,531,594 discloses the use of the combination of an organophilic cellulose material and an organophilic lignite material.

According to a third aspect of the invention, there is provided a drilling mud system for an oil well comprising a drilling mud and a material containing cellulose fibres and an inorganic filler.

The material is preferably a material according to the first aspect of the invention.

According to a fourth aspect of the invention, there is provided a method of treating lost circulation of drilling mud in an oil well comprising pumping into the well a drilling mud system. The following is a more detailed description of some embodiments of the invention, by way of example, reference being made to the accompanying drawings in which:-

Figure 1 is a schematic elevation of apparatus for treating pulp residue waste by drying and ball milling to produce a particulate material,

Figure 2 is a schematic view illustrating the circulation of drilling mud in an oil well rig,

Figure 3 is a schematic view of an apparatus for testing seepage of a drilling mud combined with a cross- circulation fluid formed using the apparatus of Figure 1,

The apparatus shown in Figure 1 is for treating pulp residue waste. Such pulp residue waste has as its principal solid components cellulose fibres and inorganic fillers in the form of kaolin clays and calcium carbonate. In general, the dry matter of the waste comprises 20%-70% by weight of inorganic filler with not less than 30% by weight of cellulose fibres. Typically, there may be 30% by weight of inorganic fillers with the remainder being cellulose fibres. The apparatus shown in Figure 1 comprises in series a holding tank 10, a screw press 11, a dryer 12, a ball mill 13 and a classifier 14. The screw press 11 is of known type. The dryer 12 may be a louvred rotary dryer having typically an inlet temperature of 450 C and an outlet temperature of 15o°C. The ball mill 13 may be a Hardinge-type ball mill supplied by N.E.I. Derby Limited or British Rema and fitted with steel spherical balls 16. The classifier 14 may be a Delta Sizer air classifier.

The pulp residue waste is collected in the tank 10 and then passed to the screw press 11. The screw press 11 extracts water from the waste reducing the water content typically from 70% by weight of the pulp residue waste to 45% by weight of the pulp residue waste.

The partly de-watered waste is then passed to the dryer 12 where it is dried until the water content of the material is less than 7% by weight. In fact, the equilibrium moisture content of the material is about 6% by weight and so if the water content of the material is reduced significantly below 6% by weight, the material will absorb water over a period of time until the 6% by weight level is reached. When the material is required for compounding with plastics it should be less than 2% by weight free water, then the material may be passed through a twin-screw co-rotating compounder shown in broken line at 15 in Figure 1 supplied by, typically A.P.V. or Theysen and fitted with vacuum extraction to remove volatile moisture. A single screw compounder without vacuum extraction may be used when the free water level is less than 1% by weight in the material prior to processing by the compounder and when the inclusion level of the material in the compound is to be less than 25% by weight.

Where there is no compounder 15, it is advisable to have the moisture content below 7% by weight for the further ^•processing of the material in the ball mill 13. If the moisture content is significantly above 7% by weight, the material will form a paste in the ball mill 13 and will not be properly milled.

The dried material is then passed to the ball mill 13 where it is milled by the balls 16. The component of the material most amenable to milling is the inorganic fillers and milling is continued until the particle size of this component is less than 1000 microns. The cellulose fibres, not being so amenable to the ball milling process, may, of course, be longer than 1000 microns. The milled material is then presented to the air classifier 14. This classifies the milled material on the basis of the specific gravity of the organic filler particles (since these have a greater specific gravity than the cellulose fibres) and so classifies the material by particle size of the organic filler. The classifier 14 can be adjusted to allow any particular particle size to be drawn-off.

For example, if a material is drawn off at the point where 85% of the organic filter particles are less than 20 microns, a material is produced which can be useful as a filler in the plastics industry.

For one use as a lost circulation material in the oil industry, all particle sizes below 200 microns are removed and the remaining material classified by sieve analysis so that all components (both inorganic filler and cellulose fibres) above 1000 microns and below 200 microns are removed. The remaining material thus has a solid component which is a combination of inorganic filler which is up to 70% by weight of the solid component and cellulose fibres which are not less than 30% by weight of the solid component. The material also contains water of more than 7% by weight. Preferably, for use in oil well drilling, the fibre content of the dry matter is 66% by weight plus or minus 5% with the remainder being inorganic filler.

This higher percentage by weight of fibres to filler than is customarily found in the raw pulp residue waste is achieved due to the fact that the proportion by weight of fibres to inorganic filler is not constant across the classifier 14. Smaller particles in the classifier (the particles below 200 microns) tend to be predominantly inorganic filler. Accordingly, there is a greater concentration of fibres in the remaining material.

The material so formed is used in an oil well in the following way.

Referring to the schematic view of an oil well shown in Figure 2, the well comprises a drill pipe 25 carrying at a lower end thereof a drill bit 26. The drill pipe 25 is rotated and the drill bit 26 cuts a hole 27 in an underground formation. A drilling mud. in a tank 28 is pumped by a mud pump system 29 into the drill pipe 25. The mud passes down the drill pipe 25 to the drill bit 26 and then passes up the hole 27.

The function of the mud is to lubricate the drill bit 16 and to convey drilled cuttings from the drill bit 16 to the surface. In addition, the drilling mud lubricates and cools the rotating drill pipe and helps to maintain the integrity of the formations cut by the drill bit 26.

On emerging from the hole 27, the drilling mud is first deposited on a filter screen 31. This removes large particles carried by the drilling mud such as the drilled cuttings cut by the drill bit 26. Next, the drilling mud passes into a settling tank 32 where other particulates carried by the mud settle into the bottom of the tank. These are removed from the settling tank 32 through a waste 33.

The drilling mud is then passed into a degasser 34 where, under a reduced pressure, entrained gases are extracted from the drilling mud. Gas and air in the drilling mud reduce both the density of the drilling mud (and hence its protection against kicks and blow-outs) and the effectiveness of additives. Their presence also increases corrosion and wear.

The de-gassed mud is then passed into a further tank 35 from which it is pumped to a cyclone separator 36 to remove sand and silt. This may be combined with finer screening. From the cyclone separator 36, the mud passes into a further tank from which it is pumped to a centrifuge 37 to remove further particles. From the centrifuge, the- mud .is returned to the -tank 28 for re-supply to the drill pipe 25.

The formations through which the drilling mud passes can affect adversely the performance of the drilling mud. For example, in some porous formations, the base liquid of the mud (whether oil or water) can be absorbed by the formation. This reduces the liquid content of the drilling mud so increasing its viscosity and so increasing the power required from the mud pump system 29. In addition, the drill bit 26 can drill into fractured or cracked formations which allow the drilling mud to leak away. This will cause a sudden loss of pressure at the surface and can have disastrous effects on the functioning of the drill. • (since the drilling mud is no longer

« functioning effectively) . It can also - affect very adversely the formations penetrated by the drilling mud - since it is very difficult to remove drilling mud from the formations and so the passage out of the formations of oil may be reduced or prevented.

In general, losses of drilling mud of this kind are dealt with by adding to the drilling mud a loss circulation fluid. In the past, these lost circulation fluids have included fine mica and fine nut hulls. The function of these lost circulation fluids is to provide a barrier at the formation which prevents the mud seeping into the formation. It is important, however, that while they do this they do not affect adversely the properties of the drilling mud.

It has been found that by adding the material described above with reference to the drawings to the drilling mud, useful loss circulation fluid is obtained. The material disperses thoroughly throughout the drilling mud. The

3 material may be added at up to 66 kg per 0.159m (30 lbs per US barrel) of drilling mud.

A test has been developed to determine the efficiency of lost circulation fluids. The test utilizes the apparatus shown in Figure 3. This apparatus comprises a conventional low pressure API test cell 50 having a lid 51 at an upper end connected to a source 52 of air under pressure. A screen 54 closes a lower end of the cell and is arranged above a container 55. A timing device 56 is also provided.

In this test, a permeable sand medium is created to replicate a formation of a kind in which losses may occur. 200 grammes of 20-40 mesh spherical sand particles are prepared and placed in the cell 50 on the screen 54 (without paper) . The sand 56 is wetted with water and the water is allowed to seep through until the water has drained completely. A pressure of 100 psi is then applied to the cell 50 by the source 52 to eliminate free water and the cell 50 is then bled to atmosphere.

The container 55 is then placed under the cell 50 and the material 57 to be tested is placed in the cell 50. The cell 50 is closed and pressurized to 690 kPA (100 psi) by the source 52.

The application of pressure drives liquid through the sand pack in a characteristic pattern in which there is immediately a flow of liquid which is continuous. After a time, the flow ceases to be continuous and becomes discrete drops. The volume of the continuous flow (called the "spurt loss") is then measured and the time of continuous flow (called the "spurt time") is also measured. The total liquid loss (i.e. the spurt loss and the amount of the subsequent discrete drops) over a period of time of 30 minutes is also measured. In general, at least a proportion of the spurt loss is liquid present in the sand pack.

As mentioned above, it is important that any lost circulation fluid does not affect adversely the rheological properties of the drilling mud. These are conveniently measured by the plastic viscosity and the yield point of the drilling mud or the drilling mud and loss circulation fluid combined.

Nine mud systems were tested using the apparatus described above with reference to Figure 3. These mud systems were as follows:-

Mud No.l. A basic drilling mud composed of one barrel of water, 55 kg (25 lbs) of bentonite, 4.4 kg (2 lbs) of chrome lignosulphonate, 2.2 kg (1 lb) of NAOH, 0.055 kg (0.025 lbs) of xantham gum polymer sold by Kelco and 2.65 kg (120 lbs) of Barite.

Mud No.2. The drilling mud of 1 together with 11 kg per

3 0.159m (51bs per US barrel) of the material described above with reference to the drawings and having a dry solids content of 66% plus or minus 5% by weight of fibres and not less than 33% plus or minus 5% by weight of inorganic filler.

Mud No.3. Mud No.l with 22 kg per 0.159m³ (10 lbs per US barrel) of the material of Mud No.2. Mud No.4. Mud No.l with 33 kg per 0.159m (15 lbs per

US barrel) of the material of Mud No.2.

Mud No.5. Mud No.l with 66 kg per 0.159m (30 lbs per US barrel) of the material of Mud No.2.

Mud No.6. Mud No.l with 11 kg per 0.159m³ (5 lbs per US barrel) of a known lost circulation fluid.

₃ Mud No.7. Mud No.l with 22 kg per 0.159m (10 lbs per

US barrel) of a known lost circulation fluid.

₃ Mud No.8. Mud No.l with 33 kg per 0.159 (15 lbs per

US barrel) of a known lost circulation fluid.

Mud No.9. Mud No.l with 66 kg per 0.159m³ (30 lbs per US barrel) of a known lost circulation fluid.

The results are shown in Table 1.

TABLE 1

Mud Concentration Rheology Properties Sand Pack Data Spurt Time Spurt Loss Total Loss

(lbs/bbl) Pv (Pas) Yp_ Sec, ml__. ml/30min kα/0.159m3

CFL = Complete Fluid Loss

It will be seen that the base mud has a spurt time of 12 seconds and a spurt loss of 200 millilitres. In 30 minutes, there is -complete fluid loss from the base mud. In comparison, the mud systems of tests 2, 3, 4 and 5 all exhibited distinctly decreasing spurt losses. In each case, the spurt time and spurt loss was significantly lower than the corresponding spurt time and loss of the known lost circulation fluid of the corresponding concentration.

Further, for equivalent concentrations, the material of muds nos. 2 to 5 had less adverse effect on the rheological properties of the mud than the corresponding concentrations of the known loss circulation fluid of muds nos. 6 to 9. In this regard, it should be recalled that a change in the rheological properties of the mud is undesirable.

Corresponding measurements were made of muds nos. 1, 3 and

7 after hot rolling the muds at 93° (200°F) for 16 hours. This is to simulate the temperatures found in oil wells. The results are shown in Table 2.

It will be seen that mud no.3 had less effect on the yield point of the mud than mud no.7. In addition, the spurt loss of mud no.3 was significantly better than the spurt loss of mud no.7.

In practice, the material of muds nos. 2 to 5 may be added to the basic drilling mud, such as mud no.l, in a variety of ways. First, the drilling mud can be circulated without the addition of any loss of control fluid. If the viscosity of the mud increases or there is partial loss of drilling mud, the material of muds nos. 2 to 5 may be added in a volume dependent on the viscosity change or mud loss. The minimum addition will usually be 11 kg per 0.159m³ (5 lbs per US gallon).

In the case of sudden and catastrophic losses of drilling mud, a tank of mud no.6 may be prepared and pumped down the hole 27. Alternatively, the drilling mud may be permanently conditioned with the material. For example, mud no.2 may be used. This stabilizes the characteristics of the drilling mud, reducing changes of viscosity and reducing the incidence of partial losses of drilling mud (which may be, for example, 0.159m 3 to 3.18m3 (1 to 20 US barrels) /hour) .

In the case of losses so catastrophic that they cannot be controlled by, say, mud no.6, it is possible to pass into the hole 27 untreated pulp residue waste i.e. a suspension in water of inorganic fillers of 20% to 70% by weight and cellulose fibres of not less than 30% by weight.

The mechanism by which the cellulose fibre-containing material acts to prevent mud loss in formations is not known precisely. It is believed however that the fibres form a thin mat over the surface of the formation. Penetrations as small as 200 microns have been measured. As a result of this low degree of penetration, the mat can subsequently be removed relatively easily to allow oil to be recovered from the formation. This removal can be by the use of hydrochloric acid. This mechanism may be assisted by the fact that the cellulose fibres in pulp residue waste are flattened as a result of their previous processing and so inactive - i.e. they will not absorb surrounding liquids. In addition, they have a high aspect ratio (e.g. a length/diameter ratio of more than 2:1 and preferably more than 5:1). This assists in the formation of a mat of fibres. They are also fibrillated, which allows them readily to interlock and to proivde sites in which the inorganic fillers are lodged.

This can be seen clearly in scanning electron micrographs of the material - it is seen as a dense mat of long hairy cellulose fibres with the inorganic filler particles lodged in the mat. Other cellulose fibre lost circulation materials such as those made from peanut hulls, are shown by SEM to have a much lower fibre density with the fibres being shorter.

As a result of the processing by the drier 12, the material is sterile or substantially sterile. This can be significant in oil wells, because any bacteria carried into the hole can multiply within the system. This can have an adverse effect on the formation and also on the drilling mud, possibly causing oil-based muds to emulsify.

It will be appreciated that the exact relative proportions of organic filler to cellulose fibre exemplified above may be varied as required. Additives of known type may be included to modify the properties as required. The lower limit of 200 microns is not essential for use in the oil industry. In some drilling mud applications the lower limit of particle size may be smaller, for example 50 or 100 microns.

Although the material of muds nos. 2 to 5 have a maximum of 71% by weight of cellulose fibres, the proportion of such fibres may be increased. For example, the proportion of cellulose fibres may be 80% by weight.

Claims

1. A particulate material having a dry matter content of up to 70% by weight of inorganic fillers and not less than 30% by weight of cellulose fibres, and having a free water content of not more than 70%, the inorganic filler being in particulate form and having a particle size of not greater than 1000 microns.

2. A material according to claim 1 wherein the cellulose fibres are between 60% to 80% by weight of the dry matter content, the inorganic filler being between 40% and 20% by weight of the dry matter.

3. A material according to claim 1 or claim 2 wherein the free water content is 6% or less.

4. A material according to claim 3 wherein the free water content is from 1% to 5%.

5. A material according to any one of claims 1 to 4 wherein the particle size of the organic filler and the cellulose fibres is from 50 microns to 1000 microns.

6. A material according to any one of claims 1 to 4 wherein the particle size of at least 85% of the inorganic filler is less than 20 microns.

7. A material according to any one of claims 1 to 6 wherein the inorganic filler comprises kaolinite clays and calcium carbonate.

8. A material according to any one of claims 1 to 7 and produced from pulp residue waste in which the cellulose fibres are fibrillated flattened and inactive and have a length: diameter ratio of greater than 2:1.

9. A method of producing a particulate material comprising drying a mixture of dry matter and water to a free water content of less than 7% by weight, the dry matter including up to 70% by weight of inorganic fillers and not less than 30% by weight of cellulose fibres and then reducing the inorganic fillers to particulate form with a particle size of less than 1000 microns.

10. A method according to claim 9 wherein the reducing step comprises milling the dried mixture in a ball mill.

11. A method according to claim 10 wherein, after reduction in the ball mill, the milled mixture is classified to remove particulate inorganic filler having a particle size greater than 1000 microns.