WO2008071004A1

WO2008071004A1 - Drilling fluid compositions and methods of manufacturing

Info

Publication number: WO2008071004A1
Application number: PCT/CA2007/002291
Authority: WO
Inventors: Daniel Guy Pomerleau; Ronald Vertz
Original assignee: Engineered Drilling Solutions Inc.; Mcasphalt Industries Ltd.
Priority date: 2006-12-14
Filing date: 2007-12-13
Publication date: 2008-06-19
Also published as: CA2670233A1

Abstract

The present invention relates to drilling fluid compositions and methods of manufacturing drilling fluids using controlled processes in combination with a colloid mill. The methods of manufacturing drilling fluids including the use of a colloid mill enable a user to customize drilling fluid characteristics for specific drilling applications thereby maximizing the benefit of fluid and fluid additives and reducing over-application or addition of additives.

Description

DRILLING FLUID COMPOSITIONS AND METHODS OF MANUFACTURING

FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION

Drilling fluids are generally characterized as oil-based muds or water-based muds. Oil- based muds will generally include a hydrocarbon or synthetic oil component and a polar component together with an organophilic clay (OC) and one or more emulsifiers and/or salts. Generally, the hydrocarbon/synthetic component is intended to provide stability to the well bore and to prevent hydration of the formation and the polar component (usually water and a salt) is intended to de-hydrate the formation.

The emulsifiers are intended to enable the formation of an emulsion between the oil and water phases and to provide oil-wetting properties.

Organophilic clay is used as a viscosifier and emulsifier. More specifically, OCs are used to provide viscosity to and to strengthen the emulsion. The effectiveness of organophilic clays as emulsion strengthening agents is derived from the "platelet" structure of the clay particles and the exposed hydroxyl groups that loosely bond with water molecules between the platelets. By immobilizing greater amounts of water between the clay platelets, the shear strength of the emulsion is increased.

Presently, drilling fluids are manufactured using an eductor for additives and high pressure pumps with a pressure plate for mixing and emulsification. The eductor is a jet pump that uses a venturi system to create a low pressure zone or suction drawing the additive into the passing high velocity fluid. The fluid additive mixture is then directed into a pressure plate creating energy forcing the fluids and additives to mix and emulsify. The fluid additive mixture is then circulated with the pump until all the additive has been sucked into the system and the desired properties are obtained. This process is time intensive and generally does not have flexibility in controlling the drilling fluid properties. In addition, the drilling fluid product is generic often having poor end-use properties in many applications.

As is known, a drilling fluid is designed to provide a number of functions when drilling a well. These properties include: bottom hole cleaning, cuttings transport, borehole wall support, balancing formation pressure, cooling the drill bit, hydraulic power transmission, data transmission, reducing friction, torque and drag, aiding in solids removal and preventing loss circulation.

The usual engineering model used to describe a drilling fluid is the shear stress versus shear rate properties of the fluid. The Bingham Fluid calculation gives the Yield Point (YP) and Plastic Viscosity (PV) as well derived values of "n" (boundary layer profile) and "K" (Fluid consistency index) from Power Law fluid dynamics. Gel strength is another desirable characteristic that is usually measured by a rotational viscometer.

When a drilling fluid is delivered to a drilling rig, the fluid is stored in a mud tank. The drilling operators draw the drilling fluid from the mud tank as the rig starts to drill. As the drilling fluid passes through the drill bit it is subjected to high shear and generated heat as it passes through the drill bit nozzles with high energy. In the case of multi-phase drilling fluids (water-in- oil or oil-in-water) the high energy of drilling and circulating contributes to further emulsification of the dispersed internal phase and any colloid materials within the fluid such as organophilic clays (OC). As the fluid is returned to the surface, the fluid is tested for desired properties and any additives required to maintain desired properties are added. Typically, any additives are introduced to the mud tank using an eductor before re-circulation downhole. The time spent adjusting the drilling fluid at the surface to adjust the drilling fluid to obtain the desired properties is both time consuming and is often wasteful in the amount of additives utilized. In addition, if there is circulation loss into the formation, any new fluid that is added must be conditioned each time additional fluid is added.

As a result, there has been a need for improved methods of manufacturing drilling fluids in order to more efficiently impart desired drilling fluid properties for a specific application and that enable high shear mixing of drilling fluids without the need for circulating the drilling fluids downhole. SUMMARY OF THE INVENTION

In accordance with the invention, there is provided methods of manufacturing stable drilling fluids having improved rheological properties that may be mixed at a central plant and subsequently delivered to a well site.

More specifically, the invention provides a method of preparing an oil-based drilling fluid comprising the steps of: mixing a water component and an organophilic clay together; mixing the water component and organophilic clay mixture into an oil-component through a high shear mill to form an oil-based drilling fluid having improved rheological properties. The high shear mill is preferably a colloid mill that may be controlled by way of back pressure and rotor/stator gap to control residence time and particle sizes.

In further embodiments, the invention provides drilling fluid compositions prepared via the above methodologies having improved fluid property parameters including HT-HP, emulsion stability (volts), plastic viscosity and yield point.

In a still further embodiment, the invention provides a method of preparing a drilling fluid comprising the steps of preparing an oil-based part in a first tank; preparing a water-based part in a second tank; adding an organophilic clay to the oil-based part in a separate tank with an eductor to provide uniform dispersion of the organophilic clay in the oil-based part; and, introducing the organophilic clay mixture and the water-based part into a colloid mill and subjecting the mixtures to a high shear process. In further embodiments, the organophilic clay may be mixed with either or both of the oil-based part and/or water-based part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by the following description with reference to the drawing where:

Figure 1 is a schematic flow diagram of a method of the invention for creating a water- in-oil or oil-in-water drilling fluid. DETAILED DESCRIPTION

In accordance with the invention, improved drilling fluid compositions and methods of preparing such drilling fluids are described. Specifically, the present invention describes a process in which a colloid mill is utilized to introduce high shear to a drilling fluid comprised of water soluble and oil soluble components. Drilling fluids so prepared have improved functional characteristics as compared to conventional drilling fluid preparations.

In accordance with the invention, the effectiveness of organophilic clay as an emulsion strengthening agent is improved. Specifically, the invention provides a manufacturing method in which the particle size of the organophilic clay is decreased during drilling fluid manufacture which results in an improved platelet edge area for water immobilization. The results of the improved manufacturing method enable the use of less expensive OCs while simultaneously enhancing emulsion strength.

In addition, in the past, the use of OCs in oil-based drilling fluids typically required preconditioning prior of the OCs prior to use which resulted in additional costs. Such preconditioning included steps such as dehydrating, one or more sodium hydroxide washes and rehydration of the OC with a quartenary amine. In the present invention, these pre-conditioned OC products, known as wet process clays, are not required. Instead, less expensive un-conditioned OCs may be utilized whilst providing superior rheological properties in the drilling fluids.

Raw Material Preparation

The method of preparing drilling fluid compositions in accordance with the invention generally comprises two steps, namely raw material preparation and colloid mill shearing.

With reference to Figure 1, in the first step, the raw materials of the drilling fluids are blended in two parts, an oil-based part and a water-based part. In creating a dual-component solution, the water soluble components are blended in a treated water tank and circulated until fully dissolved. The OC is added to the water or oil phase in a separate tank by way of an eductor to provide rapid hydration and uniform dispersion. The OC is then circulated through the eductor in its primary storage tank and the tank is subjected to secondary agitation. Once the two solutions are conditioned, the solutions may be blended prior to injection through the colloid mill. Colloid Mill Shearing

Colloid mills generally include a rotor having blades separated by a narrow gap from a stator. Rotation of the blades adjacent the stator imparts tremendous shear energy on any fluids (oil and water phases) and solids passing through the mill which create tiny spheres of the liquid phases and solids that, depending on their properties, may be dispersed within one another. With respect to solids, such as OCs, the shearing action generates sufficient energy to over come the strong polar forces which bind the OC particles together. In addition, the colloid mill action may also break down the crystalline particles to smaller sizes.

Generally, as the particles or droplets of the dispersed phase in an emulsion (ie oil dispersed in water or water dispersed in oil) become smaller, progressively more energy is required to overcome the surface tension of the particles or droplets in order to keep the particles apart.

Preferably, a colloid mill of particular benefit in accordance with the invention has a rotor and a stator having an adjustable gap in order to allow the user to manage the particle size. The gap between the rotor and stator is typically kept between 0.001 and 0.125 inches and the speed at which the mill runs is controlled to generate the hydraulic shear at the rotor/stator interface. In some mills, speeds up to 3600 rpm can be required. The rotor and the stator are generally manufactured from an alloy with a low coefficient of thermal expansion as the heat generated by the milling action can be in excess of 70 degrees Celsius.

In the case of an oil based invert emulsion the oil-based material is typically 50 to 99.9% by weight of the total invert emulsion.

Once the materials are in their respective primary tanks, the pumps feeding the mill are turned on and valves opened forcing the material to the mill.

At the mill, the materials are metered in at the desired finished product ratios using meters and valves to control the product flows. In a preferred embodiment, the colloid mill includes an outflow valve that can be closed to restrict the flow of the product exiting the mill. It is preferred that the back pressure on the mill can be controlled in order to control the residence time of the fluids within the mill. By controlling the residence time within the colloid mill allows the operator to control the energy imparted by the shearing forces in the mixing chamber which controls both the particle size and heat within the chamber. Both actions aid in milling the emulsion to a desired particle size and uniformity. Heat generated within the mill promotes the interaction between the components and allows the emulsifiers to rapidly attach to the solid particles creating the electrostatic stabilization necessary to make the emulsion storable with materials not settling and the emulsion breaking.

Examples:

Three oil-based drilling fluids were prepared according to the following preparation methodologies and their rheological properties compared: Fluid A colloid mill preparation;

Fluid B standard vortex mixing pump with a shear plate; and

Fluid C standard vortex mixing pump with a shear plate and subsequent shearing of same fluid through a drill bit and nozzles.

The tested drilling fluids comprised 82% (w/w) oil, 12% water (w/w) and 1.2% (w/w) organophilic clay together with a calcium chloride, calcium hydroxide and super degummed canola as shown in Table 1.

Table 1-Drilling Fluid Composition, Fluids A, B and C

S.G Fluids A, B, C

Distillate 822 879 31590.0 kg

Water 1000 4597.0 kg

CaCl₂ 2350 1 160.0 kg

CaOH 2200 520.0 kg

Bentone 920 2500 475.9 kg

Super Degummed Canola 1000 209.0 kg

Total Volume (metric) 41.66 cu. m

Total Volume (US) 262.2 bbl

Total Weight 38551.9 kg

Fluid Density 925.3 kg/cu.m

Analysis

Component (parts per barrel)

Super Degummed Canola 1.76 ppb

CaOH 4.38 ppb

Bentone 920 4.01 ppb CaCl₂ 9.75 ppb

CaCl₂ 25.23%

Oil 88.72%

Water 1 1.28%

Funnel Viscosity 39 sec/1

As shown in Table 2, the rheological properties of each fluid were significantly different depending on the process by which they were made.

Table 2- Rheology Measurements, Fluids A, B and C

Rheology Measurement Fluid A Fluid B Fluid C

0600 31 10 1 1

0300 21 5 6

0200 16 3.25 4

0100 1 1 1.5 2

06 3.5 0 0

03 3 0 0

HT-HP @ 50° C 500 psi 11 ml 20.0ml 16.0ml

HT-HP @ 50° C 500 psi

< 1 mm < 1 mm < 1 mm

(cake)

Emulsion Stability 1 176 volts 200 volts 400 volts

Rheology Calculations

Bingham

Plastic Viscosity 10 m. Pas 5.0 m.Pas 5.0 m.Pas

Yield Point 5.5 Pa 0.0 Pa 0.5 Pa

Power-Law n (0600/0300) 0.562 1.000 0.874

K (0300) 0.632 0.010 0.026 n (0300/0200) 0.671 1.000 1.000

K (0200) 0.320 0.007 0.012 n (0200/0100) 0.541 1.000 1.000

K (0100) 0.684 0.005 0.012

0600 0300 0200 0100 06 and 03 are measurements of viscosity within a concentric cylinder viscometer at varying shear rates and show a higher viscosity for fluid A at each shear rate.

HT-HP is a measure of the ability of the fluid to seal a porous substrate under fixed pressure and temperature conditions and is a general measure of the quality of dispersion of both solids and liquids. The HT-HP (filtrate) measures the volume of filtrate that passes through a filter and the HT-HP (cake) measures the thickness of a filter cake against the filter. As shown, Fluid A showed the lowest value of HT-HP (filtrate) which indicates superior sealing of the filter paper and is an indication of the quality of the dispersion and emulsifϊcation of the solids and dispersed phase as well as a measure of the relative ability of the drilling fluid to seal off the borehole to prevent drilling fluid loss.

Emulsion stability (volts) or Critical electrical field (CEF) is a measure of the electric field strength required to induce the flow of current through an emulsion. CEF is a measure of the ability of the fluid to resist flocculation of the dispersed fluid phase to an increasing ionization field and is representative of the stability of the emulsion. As shown, Fluid A required a higher voltage to conduct electricity through the fluid thus demonstrating higher emulsion stability.

Bingham plastic viscosity is the slope of the shear stress/shear rate line above the yield point and represents the viscosity of the drilling fluid when extrapolated to infinite shear rate. As shown, fluid A showed the highest plastic viscosity.

Yield point is a measure of the yield stress extrapolated to a shear rate of zero. YP is used to evaluate the ability of a drilling fluid to lift cuttings out of the annulus. A high YP implies a non-Newtonian fluid and a fluid that carries cuttings better than a fluid of similar density but lower YP. As shown, fluid A had the highest yield point.

Other fluid parameters including power law parameters n and K were also determined, n is a measure of the fluid velocity profile and particularly the shape of the boundary layer. Fluid A showed the lowest n values indicating a flatter fluid velocity profile. Fluid A also showed the highest K values which confirm the yield point measurements.

In summary, the fluid prepared in accordance with the methods of the invention using a high shear device such as a colloid mill provided a drilling fluid having superior rheological properties as compared to a drilling fluid prepared in accordance with past methodologies. It is understood that within the context of the invention that the methods of drilling fluid preparation as described herein may be applied to other drilling fluid compositions in order to impart superior rheological properties to those drilling fluids as would be understood by those skilled in the art.

Claims

1. A method of preparing an oil-based drilling fluid comprising the steps of: a. mixing a water component and an organophilic clay together; b. mixing the water component and organophilic clay mixture into an oil- component through a high shear mill to form an oil-based drilling fluid having improved rheo logical parameters.

2. A method as in claim 1 wherein the high shear mill is a colloid mill.

3. A method as in claim 2 wherein the colloid mill includes an outlet valve for controlling the back pressure and residence time of the oil and water components in the colloid mill.

4. A method as in claim 2 or claim 3 wherein the colloid mill includes a rotor and stator having an adjustable gap.

5. A drilling fluid composition prepared in accordance with the method of any one of claims 1-4.

6. A drilling fluid composition as in claim 5 characterized by improved fluid property parameters including HT-HP, emulsion stability (volts), plastic viscosity and yield point.

7. A method of preparing a drilling fluid comprising the steps of: a. preparing an oil-based part in a first tank; b. preparing a water-based part in a second tank; c. adding an organophilic clay to the oil-based part in a separate tank with an eductor to provide uniform dispersion of the organophilic clay in the oil-based part; d. introducing the mixture from step c and the water-based part from step b into a colloid mill; and, e. subjecting the mixture from step d to a high shear process.

8. A method of preparing a drilling fluid comprising the steps of: a. preparing an oil-based part in a first tank; b. preparing a water-based part in a second tank; c. adding an organophilic clay to the water-based part in a separate tank with an eductor to provide uniform dispersion of the organophilic clay in the water-based part; and, d. introducing the mixture from step c and the oil-based part from step a into a colloid mill; and, e. subjecting the mixture from step d to a high shear process. A method as in claim 7 wherein step c further comprises adding organophilic clay to the water-based part in a separate tank with an eductor to provide uniform dispersion of the organophilic clay in the water-based part.