WO1999032573A1

WO1999032573A1 - Thermoviscosifying water based fluids; their synthesis and use in drilling fluids

Info

Publication number: WO1999032573A1
Application number: PCT/GB1998/003822
Authority: WO
Inventors: John William Chapman; Ian Christopher Ward
Original assignee: Bw Group Plc
Priority date: 1997-12-19
Filing date: 1998-12-18
Publication date: 1999-07-01
Also published as: AU1678299A; GB9726732D0

Abstract

A water based fluid in which the viscosity increases with temperature or remains essentially constant with temperature is described. The fluid is preferably a mixture of clay and a silicate. The fluid is suitable for a wide range of uses, including well drilling, and as other fluids used in the oil and gas industries.

Description

THERMOVISCOSIFYING WATER BASED FLUIDS; THEIR SYNTHESIS AND USE IN DRILLING FLUIDS

This invention relates to water based fluids in which the viscosity increases with temperature. In particular, it relates to water based drilling fluids in which the rheology increases as the mud is circulated downhole, and so increases in temperature, and spontaneously reverses on arriving at the surface and cooling.

In the drilling of a well into the earth, there is commonly employed a drill string having a drill bit connected to the lower end thereof. The drill string is rotated to rotate the drill bit and form a well or wellbore in the earth by cutting and breaking the earth formation which it contacts. Drilling fluid is conventionally circulated down the drill string and through ports provided in the drill bit and back to the surface through the annulus formed between the drill string and the wall of the well. The circulating drilling fluid performs numerous functions including removing the cuttings from the well, cooling the bit, and applying hydrostatic pressure upon the penetrated earth formation to control fluids contained under pressure therein.

Drilling "muds" having a water base are commonly employed in this situation. These muds are normally treated to provide the desired density and rheological properties. However, the search for oil and gas now requires the drilling of wells with complex geometry, eg horizontal or highly deviated rather than vertical, and highly inhibitive systems are required to stabilise the borehole once drilled. These factors, and others, place greater emphasis on the hole cleaning capabilities of the mud for successful completion.

A mud having improved hole cleaning and suspending properties at downhole temperatures is therefore desired, and thermoviscosifying properties can be conferred to the fluid by mixing a soluble silicate and a clay type mineral under controlled conditions.

In this regard it is already known that most water based fluids decrease in viscosity as the temperature increases. In many applications, eg paints and drilling fluids, additives such as polymers and clays are added to increase the viscosity of the fluid. In drilling fluids these include polyanionic cellulose, starch, xanthan gum and clay, used to give suspending and hole cleaning characteristics.

Recent references, eg EP0620649A1 and EP0583814A1 suggest that thermoviscosifying synthetic polymers suitable for use in oil wells may be synthesised. These water soluble polymers possess a low critical solution temperature ("LCST" property) and are based on so called "graft copolymers" of an organic nature.

However, this can be disadvantageous. In the present state of the art, drilling fluids (and fluids in general) formulated with conventional additives have the serious drawback of losing their suspending properties when the temperature rises. The use of conventional agents for viscosification thus creates the risk of pumping acceptable performing fluid at the surface, but finding that severe settlement and ineffective cleaning of the hole occurs downhole.

Moreover, "graft polymers" are likely to be expensive organic molecules susceptible to degradation and polluting effects.

Thus, according to one preferred aspect of the present invention there is provided a water based (drilling) fluid comprising clay gel and soluble silicate having thermoviscosifying properties over the range of temperature from 75 °F to 175°F.

Preferably the soluble silicate solution is 2:1 Si0₂ :Na₂0.

According to a second aspect of the present invention, there is provided a process for preparing a water based (drilling) fluid in which viscosity increases with temperature, the process comprising treating a clay gel with a solution of soluble silicate.

Preferably the clay gel is formed from a smectite (Bentonite) clay.

Preferably the clay is allowed to pre-hydrate in water to allow gelation to occur.

Preferably the resulting clay gel is treated with reagents chosen from the group comprising caustic soda, soluble salt and deflocculant .

Preferably the soluble salt is a monovalent ion, eg potassium chloride or sodium chloride.

Preferably the deflocculant is a low viscosity polyanionic cellulose.

Preferably the process comprises adding the soluble silicate solution to the clay gel and "activating" the mix by heat ageing.

Preferably the heat ageing is carried out at a temperature of between 50°C, more preferably 80°C, and 130°C.

Preferably the heat ageing is carried out for between 8 and 24 hours.

The viscosifying effect of the present invention is considered to be due to the formation of either a clay silicate complex, or a complex silicate that interacts with certain types of clay and that has varying solubility characteristics with temperature. Such a complex network may contain an associated component, capable of aggregating in response to an increase in temperature, coupled to a hydrophilic component or backbone.

The fluid of the present invention, when used as a drilling fluid, will be pumped normally, but at the bottom of the hole the suspending properties will be optimised such that the fluid will be capable of supporting drill cuttings that are produced. The fluid will be able to bring the cuttings to the surface more effectively. But when the fluid is passed through the shaker screens the cooled fluid will have lost a significant part of its suspending properties and so allow the separation of cuttings to be facilitated.

It will also be noted that the invention provides a means of overcoming other problems, particularly relating to deposition, found in other industries and products and where a temperature differential exists in applications, eg paint industry, where paint may be stored or transported at high temperature. Other industries where such thermoviscosification products may find application include the coatings industry, cosmetic, food processing, lacquer and varnish industries, papermaking and cementation industries as well as in other areas of the oil and gas production and drilling industries.

Other possible uses for a fluid of the present invention are described in 098/29487 of Medlogic Global Corporation. These include medical and pharmaceutical uses such as exemplary drugs or therapeutics delivery systems, including controlled release operations, industrial and automotive uses of oils and lubricants, especially at high temperatures, cleaning products which are intended to act at high temperatures, electrical and optical wire protection, binding agents in ceramics, and other cementing applications, clothing, including footwear, as well as the further uses suggested in 098/29487.

The present invention allows an inexpensive means of producing an "inorganic" and pollution free thermoviscosifying fluid with wide application.

Further advantages are: a. A drilling fluid in which low shear rheology is generated only or in large part by the abovementioned thermoviscosifying behaviour, thus avoiding or minimising the use of special and expensive viscosifying polymers.

b. A drilling fluid in which the thermoviscous rheology is developed by activation prior to use. This allows the drilling fluid to be made onshore in a mud plant and then shipped offshore with the necessary properties for drilling.

c. Use of a said thermoviscosifying fluid in combination with a non-ionic polymer viscosifier such as a waxy starch or conventional starch incorporated for fluid loss control.

While further modifications and improvements may be made without departing from the scope of this invention, the following is a description of examples (only) of the present invention, with reference to the accompanying graphs, in which:

Graph 1 shows viscosity v. shear rate of a mud prepared using silicate solution at different temperatures (initial viscosity before 93 °C) ;

Graph 2 shows viscosity v. temperature of the mud of graph 1;

Graph 3 shows viscosity v. shear rate at different temperatures of the same mud after storage of 16 hours at 93 °C; and

Graph 4 shows viscosity v. temperature of the mud, again after 16 hours' storage at 93°C. A water based drilling fluid was produced by treating a clay gel with a solution of soluble silicate. The clay had been allowed to prehydrate in water to allow gellation to occur. The clay was a "Bentonite" type clay. The clay gel was treated with Caustic Soda, a soluble salt (Potassium Chloride or Sodium Chloride) and a deflocculant (low viscosity polyanionic cellulose) . A soluble silicate solution (eg 2:1 Si0₂:Na₂0, s.g.1.50) was added to the mixture after which the fluid was "activated" by heat ageing at 93 °C (200°F) for approximately 16 hours.

The fluid so formed was found to have thermoviscosifying properties over the range of temperature 75° to 175°C. This is thought to be due to the formation of a clay silicate complex with varying solubility characteristics. A reversible effect on the fluid viscosity via a flocculation-deflocculation mechanism leads to thermoviscosification.

Example 1

Typical thermoviscosifying formulations are shown in Table 1. The components were mixed for 30 minutes in a mixing device such as a Hamilton Beach mixer and then "aged" for 16 hours in a hot roll oven. The viscosity was determined after ageing on a Fann 35 viscometer. Table 2 shows the results obtained at three temperatures. The viscosities were found to increase as the temperature increased giving temperature coefficients (175/75°F) with positive values. The important rheological parameters used to indicate the useful rheology for antisettle and hole cleaning, the yield point and 6rpm reading, were found to increase as the temperature increased. The Newtonian component (plastic viscosity) was found to decrease slightly over this range. Upon cooling the fluids were found to lose their viscosity. Further measurements at a fixed shear rate on similarly produced fluids show the completely reversible nature of the viscosity generated, as shown in Graphs 1 to 4.

Graphs 1 and 2 indicate that, even before storage for 16 hours at 93 °C, some structure is beginning to form. The thermoviscosifying trend seems to be temperature activated and is most apparent at 170°F. From Graphs 3 and 4, it can be seen that the thermoviscosifying effect, which was starting to form at 170°F, has now been magnified. The viscosity values have increased considerably from the initial values obtained for the mud.

Fluids such as above may be used as drilling fluids or form the basis of systems used as drilling fluids or in other applications.

Table 1 : Formulations

Notes

1. 30 ppb (lb/barrel) prehydrated gel (85.7g/1000ml) Clay Gel A is European Bentonite Clay Gel B is Wyoming Bentonite

Table 2 : Rheology Profiles

Notes:

2. PV = Plastic Viscosity (cP) YP - yield point (lb/100ft²⁾

3. Fann 35 rheometer measurements.

Example 2

An unweighted mud with 15 ppb KCl brine and a < 10.0 ml fluid loss, and suitable for drilling top hole sections of wells, was prepared as follows:

Freshwater 0.02091 bbl

BW Eurogel (30 ppb pH) 245 ppb Caustic Soda 0.5 ppb Potassium Chloride 17.5 ppb Polyanionic Cellulose 1.0 ppb Sodium Silicate Solution 50.0 ppb Starch 4.0 ppb

A six laboratory barrel batch of mud according to the above formulation was made up in a Silverston mixer at 6000 rpm over 30 minutes. The mud was thermally activated by static ageing in stainless steel cells at 50°C overnight, after which one of the laboratory aliquots was contaminated with 35 ppb OCMA clay, one with 10% seawater and one with 35 ppb Barite. The muds were aged by hot rolling for 16 hours at 175°F. An additional barrel of base mud was hot rolled at 200°F. Muds were tested for rheology at 80°, 49° and 23°C before and after ageing and the API fluid loss determined.

Table 3 gives the performance data on the base mud before and after contamination with the standard contaminents . All the muds were tested before and after hot rolling at 175°F (typical ageing test to simulate downhole conditions) .

The present invention makes it possible to design drilling fluids with suspending and hole cleaning properties that meet downhole requirements. Table 3 : Contamination Tests on Activated TV Mud

Claims

1. A water based fluid in which the viscosity increases with temperature or remains essentially constant with temperature .

2. A fluid as claimed in Claim 1 in which the fluid comprises a mixture of clay, or other particulate, and a soluble or partially soluble silicate.

3. A luid as claimed in Claim 2 in which the soluble silicate solution is Si0₂:Na₂0 in the ratio 2:1.

4. A fluid as claimed in any one of Claims 1-3 in which the fluid has thermoviscosifying properties over the range of temperature from 75°F to 175°F.

5. A fluid as claimed in any one of Claims 2-4 in which the clay is a natural smectite (Bentonite) clay or a clay derived from drilled formations.

6. A fluid as claimed in Claim 5 in which the clay is pregelled in water.

7. A fluid as claimed in any one of Claims 2-6 in which the mixture includes a soluble salt of a monovalent ion.

8. A fluid as claimed in Claim 7 in which the soluble salt is potassium chloride or sodium chloride.

9. A fluid as claimed in any one of Claims 2-8 in which the mixture includes a caustic alkali or other pH affecting component.

10. A fluid as claimed in Claim 9 in which the caustic alkali is sodium hydroxide or potassium hydroxide.

11. A fluid as claimed in any one of Claims 2-10 in which the mixture includes a thinner or deflocculant .

12. A fluid as claimed in Claim 11 in which the thinner or deflocculant is a low viscosity polyanionic cellulose or tetrasodium pyrophosphate or terapotassium pyrophosphate.

13. A fluid as claimed in any one of the preceding Claims in which the mixture is activated by heat ageing.

14. A fluid as claimed in Claim 13 in which the heat ageing is carried out at a temperature of between 50°C and 130°C.

15. A drilling fluid or mud wholly, substantially or partially comprising a thermoviscosifying fluid as claimed in any one of the preceding Claims .

16. A drilling fluid as claimed in Claim 15 which includes one or more weighting agents.

17. A drilling fluid as claimed in Claim 16 in which the weighting agent is barium sulphate.

18. A drilling fluid as claimed in any one of Claims 15-17 which includes a water soluble polymer to increase the viscosity and control fluid loss properties.

19. A drilling fluid as claimed in Claim 18 in which the water soluble polymer is polyanionic cellulose, carboxymethyl cellulose, xanthan or natural gum, starch, or a viscosifying starch or an additional clay gellant.

20. A fluid as claimed in any one of Claims 1-14 for use in the oil industry at the completion stage of drilling wells, or as a "drill-in" fluid, or other fluid used at the production stage in oil or gas bearing formations.

21. A fluid as claimed in any one of Claims 1-14 for use in the formulation of a highly viscous "pill", "plug", "sweep", "spotting fluid" or "milling fluid" used in oil well drilling.

22. A fluid as claimed in any one of the preceding Claims being a solid material, and able to provide thermoviscosifying properties to a suitable aqueous base fluid when admixed therewith.

23. A process for preparing a water based drilling fluid in which the viscosity increases with temperature, the process comprising treating a clay gel with a solution of soluble silicate.

24. A process as claimed in Claim 23 in which the clay is pre-hydrated in water.

25. A process as claimed in Claim 23 or Claim 24 in which the clay gel is treated with one or more reagents selected from the group comprising caustic soda, a soluble salt, and a deflocculant.

26. A process as claimed in any one of Claims 23 to 25 in which the clay gel and silicate solution mix are activated by heat ageing.

27. A fluid whenever prepared by a process as claimed in any one of Claims 23 to 26.

28. A water based fluid substantially as hereindescribed with reference to the Examples.