WO2014047319A1

WO2014047319A1 - Oil based flocculation mixing and dispersion system

Info

Publication number: WO2014047319A1
Application number: PCT/US2013/060663
Authority: WO
Inventors: Perry D. Lomond; Diana Garcia; Gabriela FRAGACHAN; Bojan MITRIC
Original assignee: M-I L.L.C.
Priority date: 2012-09-20
Filing date: 2013-09-19
Publication date: 2014-03-27

Abstract

A system for separating drilling waste includes a first dispersion vessel configured to receive drilling waste from a pump and configured to selectively receive a polymer from a polymer supply tank, a second dispersion vessel configured to receive drilling waste from the first dispersion vessel and configured to selectively receive a surfactant from a surfactant supply tank, and a separating device configured to receive drilling waste from the second dispersion vessel. A method for separating drilling waste includes pumping drilling waste to a first dispersion vessel, injecting a polymer into the drilling waste, dispersing the polymer into the drilling waste within the first dispersion vessel, transferring the drilling waste to a second dispersion vessel, injecting a surfactant into the drilling waste, dispersing the surfactant into the drilling waste within the second dispersion vessel, and separating the drilling waste into an effluent portion and a solids portion.

Description

OIL BASED FLOCCULATION MIXING AND DISPERSION SYSTEM

BACKGROUND

[0001] Various fluids are used when drilling or completing a well, and the fluids may be used for a variety of reasons. Common uses for well fluids include: lubrication and cooling of drill bit cutting surfaces while drilling generally or drilling-in (i.e., drilling in a targeted petroliferous formation), transportation of "cuttings" (pieces of formation dislodged by the cutting action of the teeth on a drill bit) to the surface, controlling formation fluid pressure to prevent blowouts, maintaining well stability, suspending solids in the well, minimizing fluid loss into and stabilizing the formation through which the well is being drilled, fracturing the formation in the vicinity of the well, displacing the fluid within the well with another fluid, cleaning the well, testing the well, transmitting hydraulic horsepower to the drill bit, fluid used for emplacing a packer, abandoning the well or preparing the well for abandonment, and otherwise treating the well or the formation.

[0002] When returned to the surface, the mud passes through solids control equipment to remove unwanted solids. While larger solids are removed by shale shakers and hydrocyclones, low gravity solids ("LGS") (less than about 7 microns) form colloidal suspensions in the fluid and will continue to circulate through the system unless special solids removal equipment is used. The difficulty of removing these small particles increases as the particle size decreases.

[0003] Due to increasing environmental concerns and escalating disposal costs, there is growing incentive to reduce the volume of drilling wastes. At many drilling locations reserve pits are used to store drilling waste during land-based drilling operations. In certain areas that primarily use invert-emulsion drilling fluids, the waste drilling fluids stored in the reserve pits may contain hydrocarbons, solids material including colloidal particles, and free-water. In certain reserve pits, weak oil-in-water emulsions might also be present. [0004] Typically, the fluids retained in the reserve pits are disposed of by removing the fluids from the drilling location. The process of removing the retained fluids from the drilling location may be expensive and time consuming. Additionally, because the retained fluids cannot be reused in drilling operations, the cost of drilling wells in the area may be further increased due to costs associated with acquiring additional materials for building new fluids.

[0005] Accordingly, there exists a continuing need for separation equipment to separate drilled solids, water, and oil, at drilling locations.

BRIEF DESCRIPTION OF DRAWINGS

[0006] FIG. 1 shows a diagram of a separating system in accordance with embodiments disclosed herein.

[0007] FIG. 2 shows a cross-section view of a dispersion vessel in accordance with embodiments disclosed herein.

[0008] FIG. 3 shows another diagram of a separating system in accordance with embodiments disclosed herein.

DETAILED DESCRIPTION

[0009] Embodiments disclosed herein relate generally to systems and methods for recovering oil from a used drilling fluid, or "drilling waste." More specifically, embodiments disclosed herein relate to systems and methods for recovering oil from a drilling waste using a combination of chemical additives and mechanical separators.

[0010] In one aspect, embodiments disclosed herein may relate to a system for separating drilling waste, the system including a first dispersion vessel configured to receive drilling waste from a pump and configured to selectively receive a polymer from a polymer supply tank, a second dispersion vessel configured to receive drilling waste from the first dispersion vessel and configured to selectively receive a surfactant from a surfactant supply tank, and a separating device configured to receive drilling waste from the second dispersion vessel.

[0011] In another aspect, embodiments disclosed herein may relate to a method for separating drilling waste, the method including pumping drilling waste to a first dispersion vessel, injecting a polymer into the drilling waste, dispersing the polymer into the drilling waste within the first dispersion vessel, transferring the drilling waste to a second dispersion vessel, injecting a surfactant into the drilling waste, dispersing the surfactant into the drilling waste within the second dispersion vessel, and separating the drilling waste into an effluent portion and a solids portion.

[0012] Referring initially to FIG. 1, a drilling waste supply tank (not shown) may include a used oil-based drilling fluid having a diesel, synthetic, or mineral base, chemical additives, and contaminants such as, for example, silt, LGS, etc. As discussed above, drilling waste supply tank may include a drilling waste reserve pit, in which spent fluid is stored. Drilling waste may be pumped through a separating system 100 to recover the oil contained therein using chemical additives and mechanical separators.

[0013] Initially, drilling waste may be pumped through a conduit 104 into a first dispersion vessel 106 using a feed pump 108, wherein feed pump 108 may be any pump known in the art such as, for example, a positive displacement pump. Pump 108 may be selected to provide a desired fluid flow rate, or range of flow rates, and may also be selected for durability. One having ordinary skill in the art will appreciate that a pump capable of pumping a fluid including contaminants and chemical additives may be used such that the pump requires minimal maintenance in the field.

[0014] In certain embodiments, water from a first water supply tank 110 may be injected into the drilling waste prior to the drilling waste entering first dispersion vessel 106 to dilute the drilling waste, thereby decreasing its density and viscosity. The optional water injection is shown in FIG. 1 with a dashed line.

[0015] Referring now to FIG. 2, a dispersion vessel 106 in accordance with embodiments disclosed herein is shown. Dispersion vessel 106 may include a lower end 202 and an upper end 204. Lower end 202 may include a port (not shown) configured to receive drilling waste from feed pump 108 and may include additional ports (not shown) on lower end 202 configured to receive injections of base oil from a base oil storage tank 112 and injections of flocculants from a flocculant supply tank 114. Base oil may be added to the drilling waste disposed in dispersion vessel 106 to dilute the drilling waste and to decrease the density and viscosity thereof. In certain embodiments, the type of base oil that may be added to the drilling waste, namely, diesel, synthetic, mineral oil, or the like, may be selected to match the type of base-oil contained within the drilling waste.

[0016] The flocculant injected from the flocculant supply tank 114 may include a polymer configured to flocculate contaminants dispersed within the drilling waste. The flocculant may include one or more carrier fluids such as, for example, mineral oil and synthetic oil. Flocculants such as, for example, EMR-707 and EMR-958, may be used. Flocculant EMR-707 may include a cationic flocculant making up between approximately 60 weight percent and approximately 100 weight percent of the flocculant, and may further include petroleum distillates making up between approximately 10 weight percent and approximately 30 weight percent of the flocculant. While any suitable flocculant and concentration may be used, the Applicant selected EMR-707 and tested the flocculant at multiple concentrations. A range of EMR-707 concentrations that may provide maximum benefits for separating drilling waste in separating system 100 was determined. The tests and results will be discussed in detail below.

[0017] Still referring to FIGs. 1 and 2, the polymer, optional base oil, and drilling waste may be kept in dispersion vessel 106 for a particular residence time to allow dispersion of the polymer and optional base oil into the drilling waste. In certain embodiments, a residence time of at least approximately 1.5 minutes in first dispersion vessel 106 may provide acceptable dispersion results; however, other residence times may also be used. In certain embodiments, a flow rate of drilling waste through separating system 100 may be controlled to vary residence time of the drilling waste within first dispersion vessel 106. [0018] Dispersion vessel 106 may include a motor (not shown) and the motor may be driven by an adjustable speed drive ("ASD") such as, for example, a variable frequency drive ("VFD"), or a variable speed drive ("VSD"). The motor may be connected to a central shaft 208 having a plurality of paddles 210 disposed thereon. The motor may rotate central shaft 208 and paddles 210, thereby mixing the drilling waste, polymer flocculant, and base oil. The motor (not shown) may rotate central shaft 208 and paddles 210 at a speed between approximately 40 to approximately 150 rotations per minute ("rpm"). In embodiments having an ASD, multiple settings may be included, each setting corresponding to a different rotational speed. For example, a low setting may correspond to approximately 43 rpm, a medium setting may correspond to approximately 90 rpm, and a high setting may correspond to approximately 147 rpm. Those of ordinary skill in the art will appreciate that other speeds may be used and that additional or fewer speed settings may be included.

[0019] As the drilling waste is stirred by paddles 210, baffles 212 may guide the drilling waste from lower end 202 to upper end 204 of first dispersion vessel 106. One of ordinary skill in the art will appreciate that although four semicircular baffles 212 are shown in FIG. 2, any number of baffles having any desired shape may be used. Drilling waste may exit first dispersion vessel 106 from upper end 204 into a conduit 118 after the desired residence time is reached. Those of ordinary skill in the art will appreciate that the residence time of the drilling waste within first dispersion vessel 106 may be controlled by the flow rate of the drilling waste and additives, the speed of the motor, and the design of baffles 212 and paddles 210. For example, a drilling waste having relatively high density and viscosity may take longer to pass through first dispersion vessel 106 than a drilling fluid having relatively low density and low viscosity. As discussed above, the density and viscosity of the drilling waste may be altered using water and/or base oil injections. Additionally, drilling waste passing through a dispersion vessel having a low speed motor, small paddles, and numerous baffles may reside within the dispersion vessel longer than a drilling waste passing through a dispersion vessel having a high speed motor, large paddles, and few baffles. Design variables such as motor speed, paddle size, paddle design, number of paddles, baffle size, baffle design, and number of baffles may be adjusted to control the residence time of a polymer and drilling waste. Additionally, flow rate of the drilling waste through the system may be adjusted to provide a particular residence time of the polymer and drilling waste within first dispersion vessel 106.

[0020] Polymer treated drilling waste may be pumped from first dispersion vessel 106, through conduit 118, to a second dispersion vessel 120. In certain embodiments, water from a second water supply tank 122 may be injected into the drilling waste mixture through conduit 118 to dilute the drilling waste and polymer mixture. The optional water injection is shown in FIG. 1 with a dashed line. In certain embodiments, water may be injected into conduit 118 from first water supply tank 110 such that one tank injects water at multiple points in separating system 100. In yet another embodiment, a single water supply tank may be configured to provide water at multiple locations in separating system 100. For example, in such an embodiment, the single water supply tank may be connected at either a first location or a second location as desired. When the single water supply tank is connected at the first location, a conduit segment may be installed at the second location such that continuity of the fluid flow path in separating system 100 is maintained. Similarly, when the single water supply tank is connected at the second location, a conduit segment may be installed at the first location.

[0021] Polymer treated drilling waste may be pumped from conduit 118 to second dispersion vessel 120 through a lower end thereof, as discussed above with respect to first dispersion vessel 106. Second dispersion vessel 120 may also include a port (not shown) disposed on a lower end allowing for the injection of a surfactant from a surfactant supply tank 124. In certain embodiments, second dispersion vessel 120 may include a second port connected to a spare base oil supply tank 126, the spare base oil supply tank 126 being configured to selectively inject a base oil into the drilling waste disposed in second dispersion vessel 120. As discussed above, the injected base oil may be selected to match the base oil contained in the drilling waste, such as, for example, diesel, synthetic, or mineral oil. [0022] Surfactant supply tank 124 may contain surfactants such as, for example, diester sulfosuccinate, sodium dodecylbenzenesulfonate, polyethoxylated polypropoxylated CI 2- 15 alcohols, other alkosylated fatty alcohols, poly (oxy-1,2- ethanediyl, C9-11, ethoxylated alcohol, other anionic or nonionic surfactants, alkyl polyglycosides, and combinations thereof. Tests to determine an optimum concentration of a selected surfactant, namely, E-4725 provided by Kemira of Atlanta, Georgia, were performed. The tests and results will be discussed in detail below.

[0023] As discussed above with respect to first dispersion vessel 106, second dispersion vessel 120 may include baffles and a motor configured to transfer rotation through a central shaft to a plurality of paddles, thereby stirring the polymer treated drilling waste disposed within second dispersion vessel 120. Polymer treated drilling waste and injected surfactant may be kept in second dispersion vessel 120 for a desired residence time such as, for example, at least about 1.5 minutes; however, those having ordinary skill in the art will appreciate that other residence times may be used. A given residence time of fluid within the dispersion vessel may be achieved by controlling motor speed, drilling waste density and viscosity, paddle and baffle design and size, and fluid flow rate through the dispersion vessel. Additionally, as discussed above, residence time of the drilling waste within second dispersion vessel 120 may be varied by controlling a flow rate of the drilling waste through separating system 100.

[0024] Drilling waste may be pumped from an upper end of second dispersion vessel 120 into a conduit 128 in fluid communication with a separating device 130. Separating device 130 may include an aging tank, a centrifuge, or a hydrocyclone. In a system having an aging tank, the drilling waste may be kept in the aging tank for any desired amount time such as, for example, between approximately 2 and approximately 24 hours, to allow polymer and surfactant additives to act and to allow settling of the drilling waste. In certain embodiments, separating device 130 may be used to separate drilling waste into a solids phase and an effluent phase, or alternatively, separating device 130 may be used to separate drilling waste into an effluent phase and an oil phase. In certain embodiments, the effluent phase may consist entirely of oil, and a separating device may not be necessary.

[0025] Tests were conducted to determine the effect of centrifuge speed and centrifuge residence time on separating the drilling waste fluid into a solids phase and an oil phase including base oil. In certain embodiments, the oil phase may also include water. The separation of solids from oil may be measured by determining a percentage of oil recovered from the sample and by determining a density of the recovered oil. The percentage of oil recovered from the sample provides information relating to the amount of oil entrained within the solids phase. For example, a high percentage of recovered oil may indicate that a low percentage of oil is entrained within the separated solids phase, while a low percentage of recovered oil may indicate that a high percentage of oil is entrained within the separated solids phase. The density of the recovered oil provides information relating to the amount of solids such as, for example, low gravity solids, suspended within the separated oil phase. For example, recovered oil having a density higher than the density of the pure base oil may be determined to include a relatively large quantity of solids suspended therein, while a recovered oil having a density approximately equal to the density of the pure base oil may be determined to include a relatively small amount of solids suspended therein. Tests and results will be discussed in detail below.

[0026] Referring now to FIG. 3, a separating system 300 in accordance with embodiments disclosed herein is shown. Drilling waste may be pumped through a conduit 306 into a first dispersion vessel 310 using a pump 304. In certain embodiments, water from a water supply tank 308 may be injected into the drilling waste before the drilling waste enters first dispersion vessel 310, as indicated by a dashed line. As discussed above, water may be injected to change the viscosity and density of the drilling waste. A polymer and a base oil may also be injected into first dispersion vessel 310 from polymer storage tank 314, and base oil supply tank 312, respectively. In certain embodiments, the polymer may include a polymer such as, for example, EMR-707. [0027] As discussed above, the drilling waste and polymer mixture may be kept in first dispersion vessel 310 for a particular residence time such as, for example, at least approximately 1.5 minutes, to allow dispersion of the polymer and the optional water and base oil into the drilling waste. A motor (not shown) may power a mixing system to agitate the mixture of drilling waste and polymer, thereby providing dispersion of the polymer into the drilling waste. First dispersion vessel 310 may further include a plurality of baffles, as discussed above, that may guide the polymer treated drilling waste from a bottom to a top of first dispersion vessel 310.

[0028] From first dispersion vessel 310, the polymer treated mixture may be pumped through a conduit 316 to a second dispersion vessel 318 where a surfactant may be injected from a surfactant supply tank 320. In certain embodiments, the surfactant may be injected into a bottom portion of second dispersion vessel 318 and may be dispersed within the polymer treated drilling waste over a particular residence time within second dispersion vessel 318. The polymer and surfactant treated drilling waste may exit a top portion of second dispersion vessel 318 into a conduit 322 and may be pumped into a third dispersion vessel 324. In certain embodiments, a secondary polymer may be injected into a lower portion of third dispersion vessel 324 from a second polymer supply tank 326 and may be dispersed within the polymer and surfactant treated drilling waste during a residence time within third dispersion vessel 324. In certain embodiments, residence times in second dispersion vessel 318 and in third dispersion vessel 324 may be at least approximately 1.5 minutes. As discussed above, a residence time may be adjusted by multiple balancing variables including, for example, flow rate of fluid through separating system 300, density, and viscosity of the drilling waste and additives, the speed of the motor, and the design of the dispersion vessel.

[0029] The drilling waste treated with a first polymer, a surfactant, and a second surfactant may exit third dispersion vessel 324 through a top portion thereof and may be pumped through a conduit 328 to an aging tank 330. The treated drilling waste may be allowed to settle in aging tank 330 for a particular time, until a desired separation of fluid phases is achieved. For example, in certain embodiments, the treated drilling waste may be left in aging tank 330 for between approximately 2 and approximately 24 hours until a relatively low density layer separates from a relatively high density layer. In certain embodiments, aging tank 330 may include a weir (not shown) dividing aging tank 330 into at least two compartments. A first compartment may be configured to receive treated drilling waste and a second compartment may be configured to collect a relatively low density component of the drilling waste that may flow across a top of the weir. In such an embodiment, the high density layer may be made up of high gravity solids having a size greater than approximately 7 microns. The high density layer may be removed from aging tank 330 and may exit separating system 300 as shown by arrow 332.

[0030] The low density layer may be pumped through a conduit 334 to a centrifuge 336 for further separating into a solids phase 338 and a liquid phase 340, wherein the solid phase may be primarily made up of low gravity solids having a size smaller than approximately 7 microns. In certain embodiments, the recovered low gravity solids may include weighting agents that may have been added to the drilling fluid during use in drilling operations. The residence time of the low density layer within centrifuge 336 may be varied and the speed at which centrifuge 336 operates may also be varied. Tests to determine an optimal range of centrifuge residence times and centrifuge speeds were conducted and will be discussed below in detail. In select embodiments, the liquid phase 340 may be pumped to a separation tank (not shown) and may be further separated into an oil component and a water component.

[0031] In certain embodiments, a separating system in accordance with embodiments disclosed herein may include a plurality of data collection devices such as, for example, temperature sensors configured to measure temperature, flow meters configured to measure flow rates, and probes configured to measure chemical content. Separating system 100 may further include control valves configured to control fluid flow. The data collection devices may be positioned at multiple locations within separating system 100 to gather, store, and/or send information characterizing the drilling waste at multiple points within separating system 100. [0032] In select embodiments, the information obtained from the data collection devices and multiple control valves may be used to automate separating system 100. The injection of polymer and surfactant into the drilling waste may be controlled by a programmable logic controller ("PLC"). The PLC may regulate the dispersion of the polymer into the first dispersion vessel by controlling a polymer injection pump and a surfactant injection pump. Those of ordinary skill in the art will appreciate that a pump such as, for example, a positive displacement pumps and/or a diaphragm pump may be used. In alternate embodiments, the PLC may also control other processes and/or equipment in the system, such as, for example, a pump responsible for controlling the flow rate of the drilling waste through the separating system.

EXAMPLES

[0033] Several tests were conducted to obtain data characterizing the separating capabilities of a system using different drilling muds, polymer concentrations, surfactant concentrations, flow rates, and motor speeds.

Example 1 : Synthetic Drilling Fluid Tests and Results

[0034] In a first set of tests, waste samples of a low-viscosity synthetic drilling fluid,

NOVAPLUS®, commercially available from M-I L.L.C., Houston, Texas, were treated using a separating system in accordance with embodiments disclosed herein. The pure base oil included in NOVAPLUS® has a density of approximately 6.58 pounds per gallon ("ppg"). The polymer EMR-707 was injected into a first dispersion vessel and the surfactant E-4725 was injected into a second dispersion vessel. Thus, the polymer was introduced into the drilling waste before the surfactant. Polymer concentrations of 1.5% and 3% were tested with surfactant concentrations of 1.5% and 3%, respectively. Additionally, a VFD was tested at low, medium, and high speeds corresponding to approximately 40 rpm, 93 rpm, and 147 rpm, respectively. Tests varying the flow rate of drilling waste from 1.0 gallons per minute ("gpm") to 0.5 gpm were also conducted. Results of the tests can be seen in Table 1 below:

[0035] As seen in Table 1, Test 6, using EMR-707 at a concentration of 1.5%, E-4725 at a concentration of 1.5%, flow rate at 1 gpm, and motor speed at 93 rpm, yielded both the highest oil recovery percentage at 95.20%) and the lowest recovered oil density at 6.8 ppg. Thus, of the tests performed, Test 6 provided optimum separation of the drilling waste sample into a solids phase and an oil phase. Test 6 removed the highest amount of solids from the drilling waste sample and the removed solids included the lowest quantity of retained oil.

Example 2: Diesel Drilling Fluid Tests and Results

[0036] In a second set of tests, samples of VERSADRIL® drilling fluid, a diesel-based mud commercially available from M-I L.L.C., Houston, Texas, were treated using combinations of a polymer and a surfactant at different concentrations. In these tests, polymer EMR-707 and surfactant E-4723 were used. Polymer and surfactant concentrations of 1.5% and 3% were tested, and a motor having an ASD was used to determine the effect of mixing speed on recovered oil percentages and densities. A flow rate of 1 gpm was used throughout the testing. The pure base oil of the sample used in the tests below had a density of approximately 7.00 ppg. Test variables and results are shown in Table 2, below, in terms of percent oil recovered and density of the recovered oil. TABLE 2: VERSADRIL® Drilling Fluid Test Results from Stage 6 Test Set-up

[0037] As can be seen in Table 2, Test 3, having polymer and surfactant concentrations of 3% and a motor speed of 147 rpm, yielded the highest oil recovery percentage at 96.38%, while Test 1, having polymer and surfactant concentrations of 3% and a motor speed of 40 rpm, produced the lowest recovered oil density at 7.08 ppg. Thus, the parameters of Test 3 provided the highest amount of recovered oil while the parameters of Test 1 provided the highest amount of recovered solids. In the tests having polymer and surfactant concentrations of 1.5%, motor speed did not affect oil recovery percentages.

[0038] In certain embodiments of separating system 100, drilling waste may be diluted with a pure base oil. Tests were performed to determine the effect of dilution on drilling waste separation. Multiple tests were performed with variables including polymer and surfactant concentrations, motor speed, and percentage of oil dilution. Because VERSADRIL® is a diesel-based drilling fluid, diesel oil was used to dilute the drilling waste samples. Test parameters and results are shown in Table 3 below:

TABLE 3: VERSADRIL® Drilling Fluid Test Results including Diesel Oil Dilution

%

Motor Recovered

Test Polymer Surfactant Diesel % Oil

Polymer Surfactant Speed Oil Density No. Concentration Concentration Oil Recovery

(rpm)

Dilution (ppg)

1 EMR-707 2% E-4723 2% 10.0 93 65.05 7.52 2 EMR-707 2% E-4723 2% 15.0 93 74.30 7.49 3 EMR-707 2% E-4723 2% 20.0 93 76.54 7.48

4 EMR-707 3% E-4723 2% 10.0 93 74.43 7.62 5 EMR-707 3% E-4723 2% 15.0 93 70.39 7.31 6 EMR-707 3% E-4723 2% 20.0 93 76.70 7.54

7 EMR-707 3% E-4723 3% 10.0 93 55.99 7.41 8 EMR-707 3% E-4723 3% 15.0 93 61.17 7.35 9 EMR-707 3% E-4723 3% 20.0 93 56.72 7.31

[0039] Results of dilution tests show that separating system 100 using parameters of Test

6, namely, an EMR-707 polymer at a concentration of 3%, an E-4723 surfactant at a concentration of 2%, and a diesel oil dilution of 20%, yielded the highest percent of recovered oil at 76.7%; however, the 76.7% of recovered oil had the second highest density of the dilution tests at 7.54 ppg. Thus, while relatively little oil was trapped in the recovered solids phase, a relatively high solids content was left in the oil phase.

[0040] Tests 5 and 9 having EMR-707 polymer concentrations of 3%, E-4723 surfactant concentrations of 2% and 3%, respectively, and diesel oil dilution percentages of 15% and 20%), respectively, provided oil having the lowest density at 7.31 ppg. Based on these results, it can be determined that a relatively low solids content was left in the separated oil phases of the Test 5 and 9 drilling waste samples. However, looking to the percent of oil recovered for Test 9, it can be seen that a relatively small percentage of oil was recovered, indicating that the solids phase of the Test 9 drilling waste sample includes a high percentage of oil.

[0041] A final set of tests was conducted to determine the effect of centrifuge speed and centrifuge residence time on oil recovery percentage and recovered oil density. Samples of VERSADRIL® drilling waste were processed using a centrifuge at five different speeds, and the samples were kept in the centrifuge for times ranging from approximately 1.5 to 10.5 minutes. Results of the tests are shown in Table 4 below.

[0042] Tests 1, 2, and 3 were conducted using centrifuge speeds of 2200 rpm, 2450 rpm, and 2739 rpm, respectively, and recovered oil data was collected after 7, 8, 9, and 10 minutes in the centrifuge. Tests 4 and 5 were conducted using centrifuge speeds of 3000 rpm and 3450 rpm, respectively, and recovered oil data was collected after 1.5, 2, 2.5, 3, and 10.5 minutes in the centrifuge.

[0043] As seen in Table 4, at the lowest centrifuge speed, recovered oil percentage gradually increased over a 10 minute residence time in the centrifuge. At speeds of 2450 rpm and 2739 rpm, recovered oil percentage increased in minute 7 of the centrifuge residence time and leveled off in the remaining three minutes. Samples treated using high centrifuge speeds, namely, the 3000 rpm and 3450 rpm centrifuges, experienced a rapid increase in percent of oil recovered within the first 2 minutes of residence time and percent of oil recovered remained constant over the remaining 8 minutes of residence time. However, the additional residence time in the high speed centrifuges continued to lower the density of the recovered oil slightly.

[0044] While the highest percentage of recovered oil was achieved using the 3000 rpm and 3450 rpm centrifuges after a short residence time, the lowest recovered oil density was measured after 7 minutes in the 2200 rpm centrifuge. Thus, a high centrifuge speed may provide a separated solids phase containing a relatively low quantity of oil while a high residence time may provide an increased quantity of solids recovered from a drilling waste sample.

[0045] Embodiments disclosed herein provide for a separating system that effectively disperses chemicals such as polymers and surfactants in a drilling waste fluid, thereby allowing the chemicals to interact with the drilling waste fluid. Embodiments disclosed herein provide the dispersion and interaction using low maintenance, low cost dispersion vessels which may reduce down time of the system in the field. Additionally, in contrast to conventional separating processes known in the art, embodiments disclosed herein indicate that it may be advantageous to inject a flocculant into the drilling waste fluid before injecting a surfactant.

[0046] Although a few example embodiments have been described in detail above those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this disclosure. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words 'means for' together with an associated function.

Claims

CLAIMS What is claimed:

1. A system for separating drilling waste, the system comprising:

a first dispersion vessel to receive drilling waste from a pump and to selectively receive a polymer from a polymer supply tank;

a second dispersion vessel to receive drilling waste from the first dispersion vessel and to selectively receive a surfactant from a surfactant supply tank; and a separating device to receive drilling waste from the second dispersion vessel.

2. The system of claim 1, wherein the first dispersion vessel and the second dispersion vessel comprise a plurality of baffles.

3. The system of claim 1, wherein the first dispersion vessel is to provide a first residence time for the drilling waste and the polymer, and wherein the second dispersion vessel is to provide a second residence time for the drilling waste and the surfactant.

4. The system of claim 3, wherein the first residence time and the second residence time are at least approximately 1.5 minutes.

5. The system of claim 1, wherein the separating device is one selected from an aging tank and a centrifuge.

6. The system of claim 1, further comprising a water supply in selective fluid communication with at least one of the first dispersion vessel and the second dispersion vessel.

7. The system of claim 1, further comprising an oil supply in selective fluid communication with at least one of the first dispersion vessel and the second dispersion vessel.

8. The system of claim 1, further comprising: a plurality of temperature sensors to measure temperature of the drilling waste at a plurality of points within the system;

a plurality of flow meters to measure flow rate of the drilling waste at a plurality of points within the system;

a plurality of probes to measure chemical content of the drilling waste at a plurality of points within the system; and

a plurality of control valves to control a flow of the drilling waste through the system.

9. The system of claim 8, wherein the polymer injection and the surfactant injection are automated based on the temperature measurements, the flow rate measurements, the chemical content measurements.

10. A method for separating drilling waste, the method comprising:

pumping drilling waste to a first dispersion vessel;

injecting a polymer into the drilling waste;

dispersing the polymer into the drilling waste within the first dispersion vessel;

transferring the drilling waste to a second dispersion vessel;

injecting a surfactant into the drilling waste;

dispersing the surfactant into the drilling waste within the second dispersion vessel; and separating the drilling waste into an effluent portion and a solids portion.

11. The method of claim 10, wherein the polymer is injected directly into the first dispersion vessel and wherein the surfactant is injected directly into the second dispersion vessel.

12. The method of claim 10, wherein the polymer is injected into the drilling waste before the surfactant is injected into the drilling waste.

13. The method of claim 10, further comprising providing a first residence time for dispersing the polymer into the drilling waste within the first dispersion vessel.

14. The method of claim 13, wherein the first residence time is at least approximately 1.5 minutes.

15. The method of claim 10, further comprising providing a second residence time for dispersing the surfactant into the drilling waste within the second dispersion vessel.

16. The method of claim 15, wherein the second residence time of the surfactant and the drilling waste within the second dispersion vessel is at least approximately 1.5 minutes.

17. The method of claim 10, wherein pumping the effluent portion to a separating device comprises pumping the effluent portion to one selected from the group consisting of an aging tank and a centrifuge.

18. The method of claim 10, further comprising selectively injecting into the drilling waste at least one selected from the group consisting of water and base oil.