WO1998019976A1

WO1998019976A1 - A cement slurry and a method for the production of such a cement slurry, as well as a use for a light weight filling material as an additive in a cement slurry

Info

Publication number: WO1998019976A1
Application number: PCT/NO1997/000286
Authority: WO
Inventors: John Jamth
Original assignee: Veba As; Dennert Poraver Gmbh
Priority date: 1996-11-06
Filing date: 1997-10-30
Publication date: 1998-05-14
Also published as: NO970379D0; BR9713496A; AU4795197A; NO306711B1; NO970379L

Abstract

A water insoluble material consisting of porous particles, preferably of glass, is used as a light weight filling substance additive for a cement slurry of the kind used in cementing operations within bore holes, especially oil and gas wells, for the main purpose of letting the porous glass particles accommodate water prior to the material's admixture into the cement slurry or subsequent to this admixture, so that extra water is held in readiness within the cement slurry admixed said filling substance. The cement slurry will then, upon hydration and deficiency of water, be able to absorb extra water from the pores of the porous particles, thus counteracting the cement slurry's liability to shrinkage.

Description

A CEMENT SLURRY AND A METHOD FOR THE PRODUCTION OF SUCH A CEMENT SLURRY, AS WELL AS A USE FOR A LIGHT WEIGHT FILLING MATERIAL AS AN ADDITIVE IN A CEMENT SLURRY

The present invention relates to a cement slurry for use in cementing operations taking place in bore holes, particularly in oil and gas wells. Also, the invention relates to a method for the production of such a cement slurry, e.g. immediately before the use thereof in connection with cementing operations in bore holes, etc. Likewise, the invention deals with a special use for a light weight material as additive/filling material in a cement slurry, in order to reduce the total specific weight of the finnished cement slurry and its tendency to shrink upon hydration.

Especially in offshore drilling for oil and gas, it often happens, particularly during preliminary drilling, that one encounters so bad and weak formation in the top hole portion that use of ordinary cement slurry with its relatively high specific weight might have unfortunate consequences: Due to the cement slurry weight, a hydraulically based fracturing of the formation might be started. The accumulated weight of the cement slurry locally may be so high that the surrounding weaker formation does not stand the weight load at all, but fractures and opens. This may result in the formation of enormous holes in the formation which may seem to be fathomless, and which might receive enormous amounts of cement slurry pumped down therein. In single cases, the conditions may be so hopeless that one does not receive any cement slurry in return up to the seabed, irrespectively of how large amounts of cement slurry that are pumped down through the bore hole.

In order to remedy such dramatic situations, especially during the preliminary drilling operations, it has been suggested to add filling materials having a very low specific weight to the cement slurries used, thereby lowering the total density and specific weight of the finnished cement slurry.

Thus, as light weight filling materials to be added to cement slurries for the purpose of lowering the specific weight thereof, it is known to use balls of ceramic material mixed with large amounts of quartz dust. This known filling material has a low specific weight, to which i.a. the enclosed air volumes in the balls contribute. However, the accompanying amounts of quartz dust are dangerous to health and very unpleasant to work with.

In a HMS-DATABLAD (magazine concerning data) FOR W-6 DATED 24th May, 1996, it has been stated among the most serious danger moments associated with this light weight material/ filling material: (quote) Serious danger to health when subjected to it for a considerable period. Cancer risk upon inhalation. Concerning handling of the same material, the following is stated in the data magazine: Avoid handling resulting in the formation of dust. Should not be used in narrow rooms without good ventilation and/or the use of breathing protection.

The known light weight additive material containing ceramic balls mixed with large amounts of quartz dust would be very difficult to handle without the formation of dust, and would be impossible to handle during some ventilation conditions required in order to satisfy other needs. Good ventilation is recommended when working with materials associated with dust formation, but strong flows of air during the handling av such materials favour the dispersion of dust in general. Upon the handling of this known light weight material, the use of protection gloves, dust-tight protective glasses and also in addition suitable protective clothes, as well as thorough washing of all exposed skin at the end of every working shift is stipulated.

Such cement slurries of the kind concerned are liable to shrink quite significantly upon hydratization. However, the shrinking liability is not improved upon the admixture of the known light weight filling material. This problem is generally due to the fact that one has not been in a position to add to the cement slurry surfficiently large amounts of water originally and/or during the cementing operations.

On the other hand, said shrinkage is favoured by crushing some of the ceramic balls during the pumping operations from surface position, down into the bore hole wherein the cementing operations take place.

The shrinking is also a result of the hydrostatic pressure. During the hydratization of the cement slurry, a large shrinkage takes place because the slurry, as mentioned, suffers from shortage of water. This condition is especially unfortunate if the cementing does not include existing narrow gas pockets. When the cement slurry hydrate and a shortage of water takes place, underpressure conditions (vacuum) originate in the slurry, trying to absorb formation fluid, e.g. liquid gas. If one encounters such gas, this may prove very critical, as an uncontrolled gas blow out may take place.

It is an object of the present invention to provide a cement slurry to which is added a light weight filling material of such a nature that it, on the one hand, at least to a substantial extent, counteracts said shrinking occurrences in the cement slurry upon hydration, and that the light weight filling material, on the other hand, not at all represents any danger to health or involves disadvantages upon handling, so that the above-mentioned deficiencies, disadvantages and restrictions of uses and applications of prior art techniques are eliminated or reduced to a substantial degree, respectively.

To this end, a cement slurry contains light weight filling material in the form of porous bodies, e.g. ball-shaped bodies/particles, preferably of glass. Thus, the filling material may consist of a blow glass granulate - return glass of lower glass quality - which, according to an examination conducted by StBG Steinbruchs-Berufsgenossenschaft in Langenhagen, 19th February, 1996, was found to be amorphous (non-crystalline) . Further, this investigation showed that in the light weight filling material in question, no free crystalline silicic acid Siθ2 was present therein and that the orkers thus were running no health hazard of contracting e.g. silicosis. The light weight filling material in question as additive to cement slurries of the present kind is also quite undangerous to health, and blow glass granulates of this kind do not involve uncomfortable handling or other disadvantages either.

The chemical composition was as follows (statements in mass - %, about) CaO 11, Siθ₂ 69, Al₂0₃ 2, MgO 2, K₂0 1 Na₂0 14 according to a "sikkerhets datablad" (security data magazine) in EG-Richtlinie 91/155/EWG 1st version in 1995, from which it also appears that the material does not involve any dangers, and that first aid precautions are not required. Neither, environmental protective efforts are considered to be necessary. According to this security data magazine, this blow glass granulate consisting of porous, preferably ball- shaped/-like bodies/particles, should be protected against moisture, and kept dry, but these terms are only valid when the described glass granulate is used as an insulation material on shore. The only object of application of this glass granulate known per se has till now been as an insulation material to be used on shore, where only its light weight and non-toxic properties can be utilized.

Hitherto, the material has not been utilized due to the porosity thereof, and the efficient shrinking-counteracting properties as a constituent part of cement slurries have been considered as surprisingly within the technical field in question.

According to the present invention, the porosity/cavities of the glass bodies are utilized for the accommodation of water at one point of time and for the liberation of the water at a later time.

The glass granulates may e.g. in a dry state be admixed into a cement slurry of special cement and water, where the porosity of the glass bodies will cause that water from the cement slurry is accommodated within the cavities forming the porosity. Thus, the cement slurry may be added and can accommodate more water as compared with known mixing proportions. Upon shortage of water upon hydration, the cement slurry will draw additive water out from the porous glass bodies, so that the previously mentioned shrinkage phenomenon iε overcome or reduced to a decisive degree. Alternatively, the porous, preferably -ballshaped bodies/particles can be moistened to saturation in water before being admixed into the cement slurry. This may take place in e.g. a water-tight silo during the storage of the glass granulate.

These porous, moistened bodies more or less saturated with water will, after being admixed into a cement slurry, hold on to its advance added water until a need for it arises, namely during the hydration in the cementing process, when the cement slurry starts to become drier. Upon hydration, the cement slurry absorbs water from the pores of the filling material and counteracts, thus, shrinkage, simultaneously as the glass granulate gives off water previously accommodated within the pores thereof. Thereafter, this causes the granulate to additionally constitute a light weight share of the cement slurry.

The glass granulate is cream-coloured, free of smell and has a pH-value of 9 - 12 at 20°C and 100 grams/litre, as well as exhibiting a softening temperature of from 600°C. The granular size may vary from e.g. 0,25 til e.g. 8 millimetres, the specific weight decreases with increasing granular size, because the cavities due to the porosity constitute a larger share according to percentage of e.g. a cubic metre of large grains/particles/bodies than of a cubic metre of smaller grains.

Compared to the known ceramic balls admixed dust of quartz, the light weight filling material according to the invention consisting of porous glass bodies is considerably stronger, they having a substantially higher compressive strength and will i.a. withstand a far less lenient treatment than ceramic balls without being crushed.

Of other advantageous properties of the glass granulate in question may be mentioned that it is chemical stable, that it does react with neither acids nor lye, that it is alkali- proof, so that it without disadvantages can be used in mixtures with cement; that it is durable with regard to environmental influences of any kind, that it is temperature-proof and that it is non-combustible.

A non-restricting example of a formula for a light weight cement slurry according to the invention is as follows:

a) 100 kilograms cement, b) 29% (based on the cement weight) light weight material/ glass granulate according to the invention, c) 38 litres microblock per 100 kilograms cement; microblock being a finely powdered filling material, d) 5 litres of a fluid loss agent per 100 kilograms cement. This agent prevents water from leaving the cement slurry, as the latter may be subjected to extraction of water it contains if the cement slurry comes into contact with a porous layer of the crust of the earth, e.g. a layer of salt, e) 0,75 litre thinner per 100 kilograms cement. The thinner is added in order to make the cement slurry pumpable and may e.g. consist of cellulose, f) 1,5 litre delaying agent per 100 kilograms cement. The delaying agent, e.g. in the form of lignosulfonate, is added in order to regulate the setting time of the cement, g) 0,2 litre anti-foam agent per 100 kilograms cement. The anti-foam agent is added in order to dampen formation of foam during the stirring of the cement slurry, and h) 73.646 litre water per 100 kilograms cement.

Claims

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1. A cement slurry for use in cementing operations within bore holes, especially within oil and gas wells, said cement slurry containing a light weight filling material in the form of bodies, e.g. ball-shaped bodies, insoluble in water, c h a r a c t e r i z e d i n that said light weight filling material comprises porous bodies, preferably of glass.

2. A cement slurry as set forth in claim 1, c h a r a c t e r i z e d i n that the porous bodies, etc., have a granular size within the range 0,25 - 8 millimetres.

3. A method for the production of a cement slurry as set forth in claim 1 or 2 , in which the cement slurry iε admixed a light weight filling material in the form of bodies insoluble in water, c h a r a c t e r i z e d i n that the light weight filling material in the form of porous dry bodies, preferably of glass, is added to the cement slurry, the porous nature thereof causing the accommodation of water from the cement slurry which, thus, can be added further water before possibly "saturation" is reached, the cement slurry during the hydration absorbing back water from the porous bodies.

4. A method for the production of a cement slurry as set forth in claim 1 or 2, in which the cement slurry is admixed a light weight filling material in the form of bodies insoluble in water, c h a r a c t e r i z e d i n that the light weight filling material in the form of porous bodies, preferably of glass, is moistened with water, e.g. to "saturation" and, possibly, is kept in a moistened condition in a water-tight silo or similar container, and that thiε moisten light weight filling material is admixed into the cement slurry proper, the latter, during hydration, absorbing water from the porous bodies.

5. Use of porous bodies, preferably consisting of glass, as water insoluble light weight filling material additive into cement slurries of the kind used during cementing operations in bore holes, especially in oil and gas wells.