Use of wax in oil-based drilling fluid

Abstract

This invention relates to compositions and methods for improving the performance of invert drilling fluids. In particular, the invention relates to the use of waxes in drilling fluid compositions to improve the performance of organophilic clays within a drilling solution as well as improving seepage control.

Claims  (OCR text may contain errors)

  1. A method for controlling the viscosity of an oil and water emulsion comprising the step of introducing an effective amount of an emulsifier to an oil and water emulsion containing organophilic clay (OC) to produce a desired viscosity in the emulsion wherein the emulsifier is selected from any one of: beeswax, candelilla wax, camauba wax, ceresine wax, Montan wax, and shellac.
  2. A method as in claim 1 wherein the amount of emulsifier and organophilic clay are selected to maximize the performance of the organophilic clay for the desired viscosity.
  3. A method as in any one of claims 1 and 2 wherein the amounts of organophilic clay and emulsifier are balanced to minimize the amount of organophilic clay for a desired viscosity and the amount of emulsifier is sequentially increased to produce the desired viscosity.
  4. A method as in any one of claims 1-3 wherein the emulsifier is selected to improve the seepage control properties of the emulsion.
  5. A method as in any one of claims 1-4 wherein the emulsifier is Montan wax.
  6. A method as in any one of claims 1-5 further comprising the step of blending an effective amount of gilsonite into the emulsion for seepage control.
  7. A method as in claim 6 wherein greater than 90% of the gilsonite has a particle size of greater than 150 mesh.
  8. A method as in claim 6 wherein greater than 80% of the gilsonite has a particle size of smaller than 200 mesh.
  9. A method as in claim 6 further comprising the step of blending an effective amount of a leonardite into the emulsion as a secondary seepage control agent.
  10. A method as in claim 9 wherein the leonardite is any one of or a combination of a lignite or a coal dust.
  11. A method as in any one of claims 1-10 wherein the emulsifier is beeswax.
  12. A method as in claim 11 further comprising the step of blending an effective amount of gilsonite into the emulsion for seepage control.
  13. A method as in claim 12 wherein greater than 90% of the gilsonite has a particle size of greater than 150 mesh.
  14. A method as in claim 12 wherein greater than 80% of the gilsonite has a particle size of smaller than 200 mesh.
  15. A method as in any one of claims 11-14 further comprising the step of blending an effective amount of a leonardite into the emulsion as a secondary seepage control agent.
  16. A method as in claim 9 wherein the leonardite is any one of or a combination of a lignite or a coal dust.
  17. A drilling fluid emulsion comprising: a hydrocarbon continuous phase; a water dispersed phase; an organophilic clay; and, an emulsifier selected from beeswax, candelilla wax, carnauba wax, ceresine wax, Montan wax, and shellac to produce a desired viscosity in the emulsion.
  18. A drilling fluid emulsion as in claim 17 wherein the amounts of emulsifier and organophilic clay maximize the performance of the organophilic clay for the desired viscosity.
  19. A drilling fluid emulsion as in any one of claims 17-18 wherein the organophilic clay and emulsifier are balanced to minimize the amount of organophilic clay to produce the desired viscosity.
  20. A drilling fluid emulsion as in any one of claims 17-19 wherein the emulsifier is Montan wax and the emulsion further includes a gilsonite seepage control agent.
  21. A drilling fluid emulsion as in claim 20 wherein greater than 90% of the gilsonite has a particle size of greater than 150 mesh.
  22. A drilling fluid emulsion as in claim 20 wherein greater than 80% of the gilsonite has a particle size of smaller than 200 mesh.
  23. A drilling fluid emulsion as in claim 20 further comprising a leonardite as a secondary seepage control agent.
  24. A drilling fluid emulsion as in claim 23 wherein the leonardite is any one of or a combination of a lignite or a coal dust.
  25. A drilling fluid emulsion as in claim 17 wherein the emulsifier is beeswax and the emulsion further includes a gilsonite seepage control agent.
  26. A drilling fluid emulsion as in claim 25 wherein greater than 90% of the gilsonite has a particle size of greater than 150 mesh.
  27. A drilling fluid emulsion as in claim 25 wherein greater than 80% of the gilsonite has a particle size of smaller than 200 mesh.
  28. A drilling fluid emulsion as in claim 25 further comprising a leonardite as a secondary seepage control agent.
  29. A drilling fluid emulsion as in claim 28 wherein the leonardite is any one of or a combination of a lignite or a coal dust.

Description  (OCR text may contain errors)

USE OF WAX IN OIL-BASED DRILLING FLUID

FIELD OF THE INVENTION

This invention relates to compositions and methods for improving the performance of invert drilling fluids. In particular, the invention relates to the use of waxes in drilling fluid compositions to improve the performance of organophilic clays within a drilling solution as well as improving seepage control.

BACKGROUND OF THE INVENTION

Oil based drilling fluids and advances in drilling fluid compositions are described in applicant’s co-pending application PCT CA2007/000646 filed April 18, 2007 and incorporated herein by reference. This co-pending application describes the chemistry of organoclays and primary emulsifiers for use in various applications including oil-based drilling fluids and various compositions wherein the viscosity of the compositions may be controlled.

By way of background and in the particular case of oil muds or oil-based drilling fluids, organophilic clays have been used in the past 50 years as a component of the drilling fluid to assist in creating drilling fluids having properties that enhance the drilling process. In particular, oil-based drilling fluids are used for cooling and lubrication, removal of cuttings and maintaining the well under pressure to control ingress of liquid and gas. A typical oil-based drilling mud includes an oil component (the continuous phase), a water component (the dispersed phase) and an organophilic clay (hereinafter OC) which are mixed together to form a gel (also referred to as a drilling mud or oil mud). Emulsifiers, weight agents, fluid loss additives, salts and numerous other additives may be contained or dispersed into the mud. The ability of the drilling mud to maintain viscosity and emulsion stability generally determines the quality of the drilling mud.

The problems with conventional oil muds incorporating OCs are losses to viscosity and emulsion stability as well drilling progresses. Generally, as drilling muds are utilized downhole, the fluid properties will change requiring the drill operators to introduce additional components such as emulsifiers into the system to maintain the emulsion stability. The ongoing addition of emulsifiers to the oil mud increases the cost of drilling fluid during a drilling program. Compounding this problem is that the addition of further emulsifying agents to the oil mud has the effect of impairing the ability of OC to maintain viscosity within the drilling fluid which in turn requires the addition of further OCs which a) then further adds to the cost of the drilling fluid and b) then requires the addition of further emulsifiers.

As a result, there continues to be a need for oil-based drilling solutions that have superior viscosity and emulsion stability properties such that the viscosity and emulsion stability of the drillings solutions is both high and stable throughout the drilling program.

The current state-of-the-art in drilling fluid emulsifiers are crude tall oil fatty acids (CTOFAs). Crude tall oil is a product of the paper and pulping industry and is a major byproduct of the kraft or sulfate processing of pinewood. Crude tall oil starts as tall oil soap which is separated from recovered black liquor in the kraft pulping process. The tall oil soap is acidified to yield crude tall oil. The resulting tall oil is then fractionated to produce fatty acids, rosin, and pitch.

The main advantage of CTOFAs is that they are relatively inexpensive as an emulsifier. However, the use of CTOFAs as emulsifiers within oil muds does not produce high and stable viscosity and emulsion stability and does not allow or enable the control of viscosity while optimizing the performance of the organophilic clay.

As a result, there continues to be a need for a class of emulsifying agents that effectively increase or decrease the viscosity and stability of organoclay/water/oil emulsions to provide a greater degree of control over the fluid properties of such emulsions. More specifically, there has been a need for methods and compositions that reduce the costs associated with traditional oil-based drilling fluids whilst providing control over the properties of the composition.

Other emulsifiers as described in Applicant’s co-pending application include saturated fatty acids, blends of saturated fatty acids, blends of saturated and unsaturated fatty acids, a vegetable oil selected from any one of safflower oil, olive oil, cottonseed oil, coconut oil, peanut oil, palm oil, palm kernel oil, and canola oil and tallow oil. In addition to the design of the drilling fluid for its viscosity and emulsion stability, it is necessary that drilling fluid engineers factor into the drilling plan the cost of drilling fluid losses to the formation due to the porosity and fractures within the formation as well as fluid losses caused by the removal of drill cuttings from the well that have been coated with drilling fluid.

In many drilling fluid systems, fluid loss may cost an operator $700-$1 ,000 per m3 of drilling fluid lost based on an average drilling fluid cost of $700-$1000/ m3. As a result, in a typical 2000m drilling program, an operator may expect fluid losses in the range from 70 – 100 m3 which would cost the operator approximately $49,000 to $100,000 simply in lost fluid.

Seepage losses can be reduced, by varying degrees by adding foreign solids to the fluid. Most of the products in use today are cellulose-based, refined asphalts, calcium carbonates or specially constructed solids. The general objective in preventing seepage control is to plug or build a mat of material in, on, or near the well bore to create a seal between the drilling fluid and underground formations.

As is known, there can be many undesired side effects from solid seepage control additives that affect both the well bore and the drilling fluid properties. For example, solids added to a hydrocarbon/water emulsion may reduce the emulsion stability of the drilling fluid by consuming emulsifiers. The loss of emulsifier must then be offset with the addition of emulsifiers to maintain the desired fluid properties which results in higher fluid costs. It is also known that seepage control agents, such as calcium carbonates, have a relatively high density (typically in the range of 2600 kg/m3) that will increase the overall density of the drilling fluid. The higher density drilling fluid will increase the hydrostatic pressure against the formation and often increase the rate of losses. Further still, solid seepage control agents can degrade during the drilling process, and affect the plastic viscosity and yield point and thereby contribute to a reduction in the particle size distribution (PSD). Other seepage control agents may require that oil wetting chemicals be added to ensure the seepage control agents are oil wet also increasing the cost. Thus, while various formulations are effective in reducing some fluid losses, there continues to be a need for improved technologies to reduce seepage losses. SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a method for controlling the viscosity of an oil and water emulsion comprising the step of introducing an effective amount of an emulsifier to an oil and water emulsion containing organophilic clay (OC) to produce a desired viscosity in the emulsion wherein the emulsifier is selected from any one of: beeswax, candelilla wax, camauba wax, ceresine wax, Montan wax, and shellac.

The amount of emulsifier and organophilic clay are preferably selected to maximize the performance of the organophilic clay for the desired viscosity. The amounts of organophilic clay and emulsifier may also be balanced to minimize the amount of organophilic clay for a desired viscosity wherein the balance is achieved by sequentially increasing the amount of emulsifier to produce the desired viscosity.

The emulsifier may also be selected to improve the seepage control properties of the emulsion. Emulsifiers for improved seepage control are Montan wax and beeswax. Seepage control may also be enhanced by blending an effective amount of fine or coarse gilsonite into the emulsion for seepage control.

Seepage control may also be affected by blending an effective amount of a leonardite into the emulsion as a secondary seepage control agent. The leonardite may be any one of or a combination of a lignite or a coal dust.

The invention also provides a drilling fluid emulsion comprising: a hydrocarbon continuous phase; a water dispersed phase; an organophilic clay; and, an emulsifier selected from beeswax, candelilla wax, carnauba wax, ceresine wax, Montan wax, and shellac to produce a desired viscosity in the emulsion. In one embodiment, the amounts of emulsifier and organophilic clay maximize the performance of the organophilic clay for the desired viscosity. In another embodiment, the organophilic clay and emulsifier are balanced to minimize the amount of organophilic clay to produce the desired viscosity. Both Montan wax and beeswax are effective emulsifiers for seepage control. Seepage control may also be enhanced by additionally incorporating fine or coarse gilsonite. A secondary seepage control agent including leonardite may also be utilized. The leonardite may be any one of or a combination of a lignite or a coal dust.