DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the invention, improved drilling fluid compositions and methods of preparing the drilling fluid compositions are described. The compositions in accordance with the invention have rheological properties that enable their use as effective drilling fluid compositions.
In the context of this description, the compositions and methods described all relate to oil-based drilling solutions that, as described below, include a hydrocarbon continuous phase, a water dispersed phase, an organophilic clay and an emulsifier. The amount of hydrocarbon phase and water phase in a given emulsion may be varied from as low as 50:50 (hydrocarbon:water (v/v)) to as high as 99:1. At the lower end of this range, emulsion stability is substantially lower and the ability to alter viscosity requires that large amounts of organophilic clay be added to the mixture. Similarly, at the upper end, the ability to control viscosity within the emulsion is more difficult. As a result, an approximate hydrocarbon:water ratio of 80:20 to 90:10 (v/v) is a practical ratio that is commonly used for drilling solutions.
In this description, a representative drilling solution having a hydrocarbon:water ratio of 90:10 (v/v) was used as a standard to demonstrate the effect of emulsifiers on the organophilic clay performance, viscosity and emulsion stability. In addition, a relatively narrow range of organophilic clay ratios relative to the total mass of solution was utilized. Each of these amounts was selected as a practical amount to demonstrate the effect of altering the amount of organophilic clay and/or emulsifier relative to the other components. While experiments were not performed across the full range of ratios where such compositions could be made, it would be understood by one skilled in the art that in the event that one parameter was changed that adjustment of another parameter to compensate for the change in other parameters would be made. Thus, in the context of this description, it is understood that the change in one parameter may require that at least one other parameter be changed in order to optimize the performance of the composition. For example, if the stated objective in creating a composition for a given hydrocarbon:water ratio is to minimize the usage of organophilic clay in that composition, the worker skilled in the art would understand that adjustment of both the amount of organophilic clay and emulsifier in the composition may be required to obtain a composition realizing the stated objective and that such an optimization process, while not readily predictable, is understood by those skilled in the art.
- Experimental a) Base Solution
A base drilling fluid solution was created for testing whereby individual constituents of the formulation could be altered to examine the effect on drilling fluid properties. The base drilling fluid solution was a miscible mix of a hydrocarbon, water, organophilic clay and emulsifier. The general formulation of the base drilling solution is shown in Table 1.
Table 1 – Base Drilling Solution
*unless otherwise noted
- b) Preparation
The oil, water, calcium chloride and organophilic clay were mixed at high speed to create a highly dispersed slurry. Mixing was continued until the slurry temperature reached 700C. Emulsifiers were added to individual samples of each solution and again mixed at high speed for 3 minutes. Lime (CaO) was then added and blended for 2 minutes at high speed. The calcium chloride was added in accordance with standard drilling fluid preparation procedures as an additive to provide secondary fluid stabilization as is known to those skilled in the art. Prior to testing, the samples were subsequently heat aged in hot rolling cells for 18 – 24 hours to simulate downhole conditions.
- c) Fluid Property Measurements
Viscosity measurements were made using a Fann Variable Speed concentric cylinder viscometer and is the dial reading on the viscometer at the indicated rpm. Data points were collected at 600, 300, 200, 100, 6, and 3 RPM points.
Emulsion stability (ES) was measured using an OFI emulsion stability meter. Each measurement was performed by inserting the ES probe into the solution at 1200F [48.90C]. The ES meter automatically applies an increasing voltage (from 0 volts) across an electrode gap in the probe. Maximum voltage that the solution will sustain across the gap before conducting current is displayed as the ES voltage.
HT-HP (high temperature-high pressure) volume was measured in an HT-HP pressure cell (500 psi and 1200C) over 30 minutes. The HT-HP measurement provides a relative measurement of the permeability of a solution passing through a standard filter and provides a qualitative determination of the ability of the solution to seal a well bore and formation.
Plastic viscosity (PV) (mPa.s) was measured by a Bingham viscosity rotational viscometer. Plastic viscosity is a function of the shear stress exerted to maintain constant flow in a fluid. With drilling fluids, the plastic viscosity of the fluid provides a qualitative indication of the flow characteristics of the fluid when it is moving rapidly. In particular, plastic viscosity provides an indication of the ability of the fluid to disperse solids within the solution. Generally, a lower plastic viscosity (i.e. a lower slope in a shear vs. shear-stress plot) is preferred to optimize the hole cleaning parameters for a drilling fluid. That is, the lower the PV relative to its YP produces a greater shear thinning fluid and as a result improves hole cleaning while at the same time reducing bit viscosities and increasing rate of penetration (ROP).
Yield point (YP) is the y axis intercept of the plastic viscosity plot (shear-rate (x-axis) versus shear-stress (y-axis) plot) and describes the flow characteristics of a drilling solution when it is moving very slowly or at rest. The yield point provides a qualitative measurement of the ability of a mud to lift cuttings out of the annulus. A high YP implies a non-Newtonian fluid and a fluid that carries drill cuttings better than a fluid of similar density but lower YP.
Filter cake is the measurement of the thickness of the filter residue in an HT-HP filter press. Generally, it is preferred that the drilling fluid causes the formation of a thinner filter cake.
- Effect of Montan Wax on Fluid Parameters
A base fluid was prepared as above and increasing amounts of Montan wax added as primary emulsifier as shown in Table 2. Montan wax is a fossilized plant wax comprising non-glyceride long-chain (C24-C30) carboxylic acid esters (62-68 weight %), free long- chain organic acids (22-26%), long-chain alcohols, ketones and hydrocarbons (7-15%) and resins. It has a melting point of approximately 82-95 0C.
Table 2 – Effect of Montan Wax as Primary Emulsifier
The results shown in Table 2 indicate that with increasing Montan wax:
- the HT-HP volume is reduced;
- emulsion stability increased;
- yield point dropped; and, • the filter cake thickness decreased.
Thus, Montan wax is effective as a primary emulsifier while maintaining good fluid properties, particularly in reducing filter cake.
- Effect of Different Waxes on Fluid Parameters
A base fluid was prepared with Drillsol™ (Enerchem) as the primary phase. Drillsol is a middle distillate hydrocarbon drilling fluid. Different waxes were added to the base fluid as primary emulsifier in the amounts as shown in Tables 3 and 4. The waxes included plant, animal and mineral derived waxes including Beeswax, Candelilla, Carnauba, Ceresine, Montan, Shellac, and Crude Canola. In the past crude Canola has been successfully as an Emulsifier, HT-HP fluid loss control agent, and as a Rheology Modifier. As such, its use in this work was to provide a benchmark against which the waxes could be compared. The formulations shown in Table 3 included additional drilling fluid additives namely water, calcium chloride and lime. Table 4 shows fluid formulations as in Table 3 but without water, calcium chloride and lime.
Table 3 – Effect of Different Waxes as Primary Emulsifier within an Oil-based Drilling Fluid
Table 4 – Effect of Different Waxes on Oil/Wax Mixture
The results shown in Tables 3 and 4 indicate that each wax provided acceptable fluid properties; as compared to either the baseline fluid or to Canola Oil, for use as an oil- based drilling fluid. In particular, each of Beeswax, Candelilla, Carnauba, Ceresine, Montan, Shellac and Crude Canola showed acceptable viscosity, emulsion stability, and plastic viscosity. In the case of ceresine and crude canola, yield point, HT-HP filtrate and filter cake values were higher than normally accepted values. D. Effect of Waxes and Coal Powders as Seepage Control Agents
In addition, compositions including wax and various low density powders and blends were investigated for their effectiveness as seepage control agents.
- a) Experimental
The effectiveness of various additives as seepage control agents was measured in an API press. Mixtures were prepared and 350 ml samples of each mixture were pushed through a porous media (API Filter Paper) over a maximum 30 minute time period. The volume of filtrate passing through the porous media was measured together with the time taken. If the full volume of the mixture did not pass through the mixture, a maximum 30 minute time period was recorded. The volume of the filtrate was also recorded. A lower filtrate volume (less than 50 ml) indicated that the mixture was effective in sealing the porous media. A high filtrate volume and time period less than 30 minutes indicated that the mixture was not effective as a seepage control agent.
The additives were compared to a similar 350 ml solution containing calcium carbonate as a seepage control agent. The full volume of the calcium carbonate solution passed through the porous media in approximately 10 seconds.
The following waxes and powders were investigated as shown in Table 5:
Table 5 – Waxes/Powders
- b) Gilsonite
Gilsonite is a class of solid bitumens known as asphaltites. The properties of gilsonite include a high asphaltene content, a high solubility in organic solvents, a high molecular weight and a high nitrogen content.
Gilsonite is available in different grades generally categorized by softening point. The softening point is used as an approximate guide to its melt viscosity and behaviour in solution. The chemical differences are generally small between gilsonite grades, with only subtle variations in average molecular weight and asphaltene/resin-oil ratios. Gilsonite includes a significant aromatic fraction and most of the aromatics exist in stable, conjugated systems, including porphyrin-like structures. The remainder of the product consists of long, paraffinic chains.
The particle sizes of the fine and coarse gilsonite are shown in Figure 6A.
Table 6B shows the typical component analysis (wt %) for different gilsonites and the corresponding softening points.
Table 6A – Gilsonite Particle Size Distribution
Table 6B – Component Analysis and Softening Points of Gilsonites
Typical Component Analysis (wt %)
Asphaltenes 57 66 71 76
37 30 27 21 (Maltenes)
Oils 6 4 2 3
Total 100 100 100 100
290 320 350 375 0F
A notable feature of gilsonite is its high nitrogen content (3.3 wt%, typical), which is present mainly as pyrrole, pyridine, and amide functional groups. Phenolic and carbonyl groups are also present. The low oxygen content relative to nitrogen suggests that much of the nitrogen has basic functionality and likely accounts for the surface wetting properties and resistance to free radical oxidation. The average molecular weight of Gilsonite is about 3000. This is high relative to other asphalt products and to most synthetic resins and likely contributes to gilsonite’s “semi-polymeric” behaviour when used as a modifying resin in polymeric and elastomeric systems. There is some reactive potential in gilsonite and crosslinking and addition type reactions have been observed.
- c) Leonardites
Leonardites (also referred to as humates and lignites) include mined lignin, brown coal, and slack and are an important constituent to the oil well, drilling industry. Leonardites, as known to those skilled in the art and within this description refer to the general class of compounds. Lignite is technically known as a low rank coal between peat and sub- bituminous and is given to products having a high content of humic acid. The lignite used in the following tests was from the Dakota Deposit.
With reference to Tables 7a-7f, the effectiveness of various blends of oil, waxes and powders as seepage control agents was compared. Table 7a shows Runs 1-4 that included various blends of Montan wax, coarse or fine gilsonite, and lignite.
The results shown in Table 7a (Runs 1 and 2) compare the effectiveness of coarse and fine gilsonite as a seepage control agent in a blend including Montan wax, coarse or fine gilsonite, and lignite. The results of runs 1 and 2 show that there was no significant difference using coarse or fine gilsonite.
Runs 3 and 4 compare the effectiveness of coarse and fine gilsonite as a seepage control agent in blends including an increased amount of Montan wax and coarse and fine gilsonite in the absence of lignite. The results indicate that both coarse and fine gilsonite are very effective as a seepage control agent when blended with Montan wax. The results show that coarse gilsonite was significantly better.
Table 7b – Seepage Control Blends and Results
The results shown in Table 7b (Runs 5-10) compare the effectiveness of various waxes blended with coarse gilsonite and black earth super fine as a seepage control agent. The results indicate that those blends including Beeswax and Montan wax in a blend including coarse gilsonite and black earth super fine are effective as a seepage control agent. Blends with Carnauba, Ceresine and Candellila were not effective.
Table 7c – Seepage Control Blends and Results
The results shown in Table 7c (Runs 11-16) compare the effectiveness of blends with Montan wax together with various combinations with coarse and fine gilsonite and/or coal dusts. The results indicate that blends including coarse gilsonite and C07-392 cyclone dust, C07-393 coal dust or lignite were the most effective blends.
Table 7d – Seepage Control Blends and Results
The results shown in Table 7d (Runs 17-19) compare the effectiveness of blends of shellac together with coarse Gilsonite and various coal powders. The results indicate that blends incorporating shellac were not effective as seepage control agents.
Table 7e – Seepage Control Blends and Results
The results shown in Table 7e (runs 20-24) compared the effectiveness of blending various coal powders with Distillate 822 and no additional additives. The results show that coal powders in the absence of other additives are not effective as a seepage control agent.
Table 7f – Seepage Control Blends and Results
The results shown in Table 7f (runs 25-28) compared the effectiveness of blends including Montan wax, coarse, fine or no gilsonite and/or lignite powder or C07-393 DC- 90 coal dust. The results show that coarse or fine gilsonite together with lignite or coal dust were not effective as a seepage control agent. The results show that blends including Montan wax with lignite or coal dust were also not effective as seepage control agents. E. Results
In summary, the results show that:
- the combination of Montan wax and coarse or fine gilsonite (Runs 3 and 4) provide good SC;
- If lignite is added, SC decreases (Runs 1 and 2);
- Both Beeswax and Montan wax combined with black earth super-fine and coarse gilsonite provide good SC (Runs 5 and 9); and,
- Montan wax combined with coarse gilsonite and coal powders provide good SC (Runs 12-16).
The results show that Montan wax and Beeswax are effective seepage control agents when combined with coarse or fine gilsonite and/or various coal powders. Unexpectedly, blends including coarse gilsonite provided superior SC compared to fine gilsonite. It is believed that the compositions are effective as seepage control agents as a result of the interactions between the long-chain waxes, the plastically deformable gilsonites and insoluble coal powders. The larger gilsonite particles may provide better SC as the plastic deformation and swelling of the larger particles in the hydrocarbon phase is higher thus providing a firmer or solid matrix of particles against which insoluble coal particles can interact with. The long chain wax particles may also provide a web into which the coal particles may seat. This is contrasted with calcium carbonate that does not swell or plastically deform in the hydrocarbon phase.
A comparison of the properties of a 50/50 Montan wax/gilsonite mixture, lignite, calcium carbonate and paraffin wax are shown in Table 7.
Table 7 – Property Comparison
Importantly, the compositions in accordance with the invention enable the operator to ameliorate the cost of seepage control agents by incorporating into drilling solutions less expensive additives that are effective in seepage control. Generally, both gilsonite and Montan wax are “medium” cost products. By introducing cheaper cost coal powders, the amounts of gilsonite and Montan wax can be reduced thus lowering the overall cost of the drilling fluid while still providing an effective seepage control product.
Still further, by eliminating high density calcium carbonate, the overall density of the drilling fluid is substantially reduced thus reducing the seepage control losses due to hydrostatic pressure. By using lower density SC agents in small concentrations in base oils that have ASG’s of 760 kg/m3 to 870 kg/m3 the increase in fluid density is marginal when compared to calcium carbonate. Also these materials present advantages by their lighter density as they will remain suspended when subjected to solids separation equipment (such as centrifuges and hydrocyclones) that are used to remove high density materials drilled solids.
- Field Results
A blend of Montan wax, lignite and coarse gilsonite was field tested. Prior to introduction of the mixture, the well was observing fluid losses at approximately 2.5 m3 / hr. After the addition of the blend, fluid losses were 0.6 m3/hr. Over the course of the drilling program, it was estimated that the operator saved $200,000 in drilling fluid costs.
Although the present invention has been described and illustrated with respect to preferred embodiments and preferred uses thereof, it is not to be so limited since modifications and changes can be made therein which are within the full, intended scope of the invention.
Oil Based Mud
Oil based muds & Synthetic-Based muds:
Through this memo, we expect:
-To present the materials oil-based muds (OBMs) or synthetic-based muds (SBMs) are made of (most of the time,such muds are water-in-oil, invert, emulsions),
-To give information and field habits to effectively solve formulating problems.
Same of these information are also included in an XL-based program (currently under development) to design drilling fluids.
1-Applications Of OBMs.
OBM offers many advantages over water muds. Cost and environmental disposals can be factors in not selecting this type of mud system.
2-OBMs Basic Chemistry.
Invert emulsions (the most common OBMs)are formulated to contain moderate to high concentrations of water (up to 60% in extreme ocnditions).
Special emulsifiers are added to emulsify the water as the internal phase and prevent the water from breaking out and coalescing into larger droplets.
These water droplets,if not tightly emulsified, can water-wet the already oil-wet solids and ddramatically affect the emulsion stability.
The balanced activity concept is shortly described in annex 1.Shale swelling is a required notion to expain the need of this concept : it is briefly explained in annex 2.
BHT=bottom Hole Temperature
Oil muds require special products to ensure that the emulsion is extremely stable and can withstand conditions of HT and contaminants. Every single product must be dispersible in the external oil phase.
3-Synthetic-Based Fluids For Oil Muds Replacement.
The first use of oil as a drilling fluid is not know. It is likely,however, that someone thought of using produced crude to drill the well, assuming that would eliminate wellbore damage that can occur with water contact.
Crude oils were difficult to use as drilling fluids, so refined oils and processed asphalts replaced them .A number of mud products came into ,being to control the normal mud properties of viscosity and fluid loss and to emulsify water.