Characterization of crude oil and its fractions by thermogravimetric analysis

Abstract

A system and a method are provided for calculating the cetane number, pour point, cloud point, aniline point, aromaticity, and/or octane number of a crude oil and its fractions from the density and thermogravimetric analysis (TGA) of a sample of the crude oil.

Claims

1. A system for evaluating a crude oil sample and calculates an indicative property of a gas oil or naphtha fraction of the crude oil sample without first distilling said gas oil or naphtha fraction, the system comprising: a thermogravimetric analyzer; a non-volatile memory device that stores calculation modules and data, the data including density of the crude oil sample and TGA data from an analysis of the crude oil sample as determined by the thermogravimetric analyzer; a processor coupled to the non-volatile memory; a first calculation module that retrieves the TGA data from the non-volatile memory device, calculates a crude oil thermogravimetric analysis index from a weighted mean of mass loss percentage versus heating temperature as indicated by the TGA data, and transfers the calculated crude oil thermogravimetric analysis index into the non-volatile memory; and a second calculation module that calculates the indicative property for the gas oil or naphtha fraction of the crude oil from a two-variable polynomial equation with predetermined constant coefficients developed using linear regression techniques, and that stores the indicative property into the non-volatile memory device; wherein the two variables of the two-variable polynomial equation are the crude oil thermogravimetric analysis index and the density of the crude oil sample.

2. The system of claim 1, wherein the indicative property is a cetane number.

3. The system of claim 1, wherein the indicative property is a pour point.

4. The system of claim 1, wherein the indicative property is a cloud point.

5. The system of claim 1, wherein the indicative property is an aniline point.

6. The system of claim 1, wherein the indicative property is an aromaticity.

7. The system of claim 1, wherein the indicative property is an octane number.

8. The system of claim 1, wherein a temperature range for the TGA analyzer is 20-1000 C.

9. The system of claim 1, wherein the heating rate is in a range of 0.1-100 C./minute.

10. The system of claim 1, wherein the thermogravimetric analysis index of the crude oil is calculated at a 50 W % point of the TGA data.

11. The system of claim 1, wherein the thermogravimetric analysis index of the crude oil is calculated by taking an average of temperature data.

12. The system of claim 1, wherein the thermogravimetric analysis index of the crude oil is calculated by taking a weighted average of temperature data.

13. The system of claim 1, wherein the thermogravimetric data is obtained directly from core and/or drill cuttings material.

14. A method for evaluating a crude oil sample to determine an indicative property of a gas oil or naphtha fraction of the crude oil sample without first distilling said gas oil or naphtha fraction, the method comprising: obtaining a density of the crude oil sample; subjecting said crude oil sample to a TGA analysis using a thermogravimetric analyzer; calculating a crude oil thermogravimetric analysis index for the crude oil sample from a weighted mean of mass loss percentage versus heating temperature as indicated by a TGA data; and calculating and recording the indicative property for the gas oil or naphtha fraction of the crude oil from a two-variable polynomial equation with predetermined constant coefficients developed using linear regression techniques; wherein the two variables of the two-variable polynomial equation are the crude oil thermogravimetric analysis index and the density of the crude oil sample.

15. The system of claim 14, wherein the indicative property is a cetane number.

16. The system of claim 14, wherein the indicative property is a pour point.

17. The system of claim 14, wherein the indicative property is a cloud point.

18. The system of claim 14, wherein the indicative property is an aniline point.

19. The system of claim 14, wherein the indicative property is an aromaticity.

20. The system of claim 14, wherein the indicative property is an octane number.

21. The system of claim 1, wherein a temperature range for the TGA analyzer is 20-1000 C.

22. The system of claim 14, wherein the heating rate is in a range of 0.1-100 C./minute.

23. The system of claim 14, wherein the thermogravimetric analysis index of the crude oil is calculated at a 50 W % point of the TGA data.

24. The system of claim 14, wherein the thermogravimetric analysis index of the crude oil is calculated by taking an average of temperature data.

25. The system of claim 14, wherein the thermogravimetric analysis index of the crude oil is calculated by taking a weighted average of temperature data.

26. The method of claim 14, wherein the thermogravimetric data is obtained directly from core and/or drill cuttings material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features of the present invention will become apparent from the following detailed description of the invention when considered with reference to the accompanying drawings in which:

(2) FIG. 1 is a graphic plot of typical thermogravimetric data for typical crude oil samples with different API gravities;

(3) FIG. 2 is a block diagram of a method in which an embodiment of the invention is implemented;

(4) FIG. 3 is a schematic block diagram of modules of an embodiment of the invention; and

(5) FIG. 4 is a block diagram of a computer system in which an embodiment of the invention is implemented.

DETAILED DESCRIPTION OF INVENTION

(6) A system and a method are provided for determining one or more indicative properties of a hydrocarbon sample. Indicative properties (e.g., cetane number, pour point, cloud point, and aniline point) of a gas oil fraction and ozone number of a naphtha fraction in a crude oil sample are assigned as a function of the density and thermogravimetric measurement of the crude oil sample. The indicative properties provide information about the gas oil and naphtha properties without fractionation/distillation (crude oil assays) and help producers, refiners, and marketers to benchmark the oil quality and, as a result, valuate the oils without performing the customary extensive and time-consuming crude oil assays.

(7) The systems and methods are applicable for naturally occurring hydrocarbons derived from crude oils, bitumens, heavy oils, shale oils and from refinery process units including hydrotreating, hydroprocessing, fluid catalytic cracking, coking, and visbreaking or coal liquefaction.

(8) In the system and method herein, thermogravimetric analysis is obtained by a suitable known or to-be-developed process. Thermogravimetric analysis measures a sample's weight as it is heated or cooled in a controlled atmosphere to provide volatility information of the oil sample under investigation. TGA requires a high degree of precision in the mass change and temperature. A thermogravimetric analyzer is used, comprising a furnace that contains a sample pan that is supported by a precision balance. A sample purge gas controls the sample environment. This gas may be inert or a reactive gas that flows over the sample and exits through an exhaust. In one experiment, TGA was conducted with TA Instruments (New Castle, Del.) Model #2050, equipped with the company's Universal Analyst and Thermal Advantage software. Similar equipment can be used.

(9) The temperature range for the TGA analyzer can extend from ambient temperature (e.g., 20 C.) to an upper limit of up to 1000 C. Heating can be at a rate in the range of about 0.1-100 C./minute.

(10) The thermogravimetric analysis index used is calculated from TGA data of a sample of whole crude oil or in certain embodiments oil well drilling cuttings. In a preferred embodiment, the thermogravimetric analysis index can be calculated at the 50 W % point of the TGA data.

(11) In one embodiment, the thermogravimetric analysis index can be calculated by taking the average of temperature data. In a preferred embodiment, the thermogravimetric analysis index can be calculated by taking the weighted average of temperature data.

(12) In one embodiment, the thermogravimetric data can be obtained directly from core and/or drill cuttings material.

(13) FIG. 1 shows a graphic plot of typical thermogravimetric data for typical crude oil samples with different API gravities.

(14) FIG. 2 shows a process flowchart of steps in a method according to one embodiment herein, in which crude oil samples are prepared and analyzed by TGA according to the method 200 described below.

(15) In step 210 a sample of 15-25 mg is placed via a pipette in a commercial platinum sample pan. No sample dilution or special sample preparation is required. TGA is conducted under a nitrogen atmosphere from ambient temperature to 600 C. at 10 C./minute and a gas flow of 905 ml/min through the furnace using calibrated rotameters. A continuous flow of nitrogen (101 ml/min) through the balance chamber is also maintained.

(16) In step 215, the thermogravimetric data is arranged so that weight loss percentages (from 0 to 100) are calculated.

(17) In step 220, a Thermogravimetric analysis index (TGAI) is calculated from the mass loss percentage and the temperature according to equation (1):

(18) $\begin{array}{cc}\mathrm{TGAI}=\frac{\left[\begin{array}{c}5*T_5+10*T_{10}+20*T_{20}+30*T_{30}+40*T_{40}+50*\\ T_{50}+60*T_{60}+70*T_{70}+80*T_{80}+90*T_{90}+95*T_{95}\end{array}\right]}{\left[5+10+20+30+40+50+60+70+80+90+95\right]};& \left(1\right)\end{array}$
where T.sub.x is the temperature at individual mass loss percentage

(19) The indicative properties (e.g., the cetane number, pour point, cloud point and aniline point) of the gas oil fraction, e.g. boiling in the range of 150-400 C. and in certain embodiments in the range of 180-370 C., the octane number of the naphtha fraction, and the aromaticity for the whole crude oil (WCO), can be assigned as a function of the density and the TGAI of crude oil. That is,
Indicative Property=f(density.sub.crude oil,TGAI.sub.crudeoil)(2);

(20) Equation (3) is a detailed example of this relationship, showing the cetane number, pour point, cloud point and aniline point that can be predicted for the gas oil (GO) fraction of the crude oil, as well as the aromaticity that can be predicted for the whole crude oil (WCO), as well as the octane number that can be predicted for the naphtha fraction.

(21) In steps 235, 240, 245, and 250, respectively, the properties of a cetane number, pour point, cloud point and aniline point for the gas oil (GO) fraction of the crude oil are calculated, in step 253 the aromaticity for the whole crude oil (WCO) is calculated, and in step 255 the property of an octane number for the naphtha fraction of the crude oil is calculated. While FIG. 2 shows the steps performed sequentially, they can be performed in parallel or in any order. In certain embodiments, only one or more steps 235, 240, 245, 250, 253, 255 are carried out. In these steps, the one or more indicative properties are determined as follows:
Indicative property=K+X1*DEN+X2*DEN.sup.2+X3*DEN.sup.3+X4*TGAI+X5*TGAI.sup.2+X6*TGAI.sup.3+X7*DEN*TGAI(3);

(22) where:

(23) DEN=density of the crude oil sample; and

(24) K, X1-X7, are constants for the properties to be predicted that are developed using linear regression analysis of hydrocarbon data from TGA.

(25) FIG. 3 illustrates a schematic block diagram of modules in accordance with an embodiment of the present invention, system 300. Density and raw data receiving module 310 receives the density of a sample of crude oil and thermogravimetric analysis data derived from the crude oil.

(26) Thermogravimetric analysis index calculation module calculates the thermogravimetric analysis index from the TGA data.

(27) Cetane number calculation module 335 derives the cetane number for the gas oil fraction of the crude oil as a function of the thermogravimetric analysis index and density of the sample.

(28) Pour point calculation module 340 derives the pour point for the gas oil fraction of the crude oil as a function of the thermogravimetric analysis index and density of the sample.

(29) Cloud point calculation module 345 derives the cloud point for the gas oil fraction of the crude oil as a function of the thermogravimetric analysis index and density of the sample.

(30) Aniline point calculation module 350 derives the aniline point for the gas oil fraction of the crude oil as a function of the thermogravimetric analysis index and density of the sample.

(31) Aromaticity calculation module 352 derives the aromaticity for the whole crude oil as a function of the thermogravimetric analysis index and density of the sample.

(32) Octane number calculation module 355 derives the octane number for the naphtha fraction of the crude oil as a function of the thermogravimetric analysis index and density of the sample.

(33) FIG. 4 shows an exemplary block diagram of a computer system 400 in which the partial discharge classification system of the present invention can be implemented. Computer system 400 includes a processor 420, such as a central processing unit, an input/output interface 430 and support circuitry 440. In certain embodiments, where the computer system 400 requires a direct human interface, a display 410 and an input device 450 such as a keyboard, mouse or pointer are also provided. The display 410, input device 450, processor 420, and support circuitry 440 are shown connected to a bus 490 which also connects to a memory 460. Memory 460 includes program storage memory 470 and data storage memory 480. Note that while computer system 400 is depicted with direct human interface components display 410 and input device 450, programming of modules and exportation of data can alternatively be accomplished over the input/output interface 430, for instance, where the computer system 400 is connected to a network and the programming and display operations occur on another associated computer, or via a detachable input device as is known with respect to interfacing programmable logic controllers.

(34) Program storage memory 470 and data storage memory 480 can each comprise volatile (RAM) and non-volatile (ROM) memory units and can also comprise hard disk and backup storage capacity, and both program storage memory 470 and data storage memory 480 can be embodied in a single memory device or separated in plural memory devices. Program storage memory 470 stores software program modules and associated data, and in particular stores a density and raw data receiving module 310, thermogravimetric analysis index calculation module 315, cetane number calculation module 335, pour point calculation module 340, cloud point calculation module 345, aniline point calculation module 350, aromaticity calculation module 352, and octane number calculation module 355. Data storage memory 480 stores results and other data generated by the one or more modules of the present invention.

(35) It is to be appreciated that the computer system 400 can be any computer such as a personal computer, minicomputer, workstation, mainframe, a dedicated controller such as a programmable logic controller, or a combination thereof. While the computer system 400 is shown, for illustration purposes, as a single computer unit, the system can comprise a group of computers which can be scaled depending on the processing load and database size.

(36) Computer system 400 preferably supports an operating system, for example stored in program storage memory 470 and executed by the processor 420 from volatile memory. According to an embodiment of the invention, the operating system contains instructions for interfacing computer system 400 to the Internet and/or to private networks.

EXAMPLE 1

(37) A set of constants K and X1-X7 was determined using linear regression for the indicative properties cetane number, pour point, cloud point, aniline point, octane number, and aromaticity. These constants were determined based on known actual distillation data for plural crude oil samples and their corresponding indicative properties. These constants are given in Table 3.

(38) TABLE-US-00003 TABLE 3 Constants Cetane Number Pour Point Cloud Point Aniline Point Octane Number WCO-AROM K 3.4440824E+06 4.8586818E+06 2.9180642E+05 1.5741617E+06 3.1407161E+05 1.2131981E+05 X1 1.1648748E+07 1.6445177E+07 9.9096539E+05 5.3253923E+06 1.1079386E+06 4.1952545E+05 X2 1.2971167E+07 1.8314457E+07 1.1102599E+06 5.9279491E+06 1.2925048E+06 4.7011378E+05 X3 4.7663268E+06 6.7294243E+06 4.1141986E+05 2.1769469E+06 5.0229227E+05 1.7360561E+05 X4 3.4781476E+02 5.1784158E+02 2.4644626E+01 1.6833776E+02 2.1800822E+01 3.0649367E+01 X5 3.0996298E01 4.9994583E01 2.4183985E02 1.6081980E01 6.9721231E02 6.2885397E02 X6 3.1335567E04 5.0732788E04 2.4017172E05 1.6443813E04 7.3440477E05 6.4167386E05 X7 2.8259387E+02 4.0725036E+02 1.9062052E+01 1.3337068E+02 0 1.1934777E+01

(39) The following example is provided to demonstrate an application of equation (3). A sample of Arabian medium crude with a 15 C./4 C. density of 0.8828 Kg/l was analyzed by TGA, using the described method. The tabulated results follow in Table 4:

(40) TABLE-US-00004 TABLE 4 API = 27.4 W % Temperature, C. 0 21 1 23 2 28 3 34 4 40 5 46 6 51 7 56 8 61 9 66 10 71 11 76 12 81 13 86 14 90 15 95 16 100 17 104 18 109 19 114 20 118 21 123 22 127 23 132 24 136 25 141 26 145 27 150 28 154 29 158 30 163 31 167 32 171 33 176 34 180 35 184 36 188 37 193 38 197 39 201 40 205 41 209 42 214 43 218 44 222 45 226 46 230 47 235 48 239 49 243 50 247 51 252 52 256 53 260 54 264 55 269 56 273 57 277 58 282 59 286 60 291 61 295 62 300 63 304 64 309 65 314 66 319 67 324 68 329 69 334 70 339 71 344 72 350 73 355 74 360 75 366 76 372 77 380 78 392 79 411 80 423 81 434 82 444 83 450 84 457 85 464 86 471 87 481 88 496 89 516 90 530 91 539 92 547 93 553 94 559 95 564 96 569 97 574 98 579 99 584 100 595

(41) Applying equation (1), TGAI was calculated to be:

(42) $\begin{array}{c}\mathrm{TGAI}=\frac{\left[\begin{array}{c}5*T_5+10*T_{10}+20*T_{20}+30*T_{30}+40*T_{40}+50*\\ T_{50}+60*T_{60}+70*T_{70}+80*T_{80}+90*T_{90}+95*T_{95}\end{array}\right]}{\left[5+10+20+30+40+50+60+70+80+90+95\right]}\\ =[5*46+10*71+20*118+30*163+40*205+50*247+\\ 60*291+70*339+80*423+90*530+95*564]/\\ \left[5+10+20+30+40+50+60+70+80+90+95\right]\\ =205,060/550\\ =372.8363\end{array}$

(43) The TGAI was therefore calculated to be 372.8363.

(44) Applying equation (3) and the constants from Table 3:
Cetane Number.sub.GO(CET)=K.sub.CET+X1.sub.CET*DEN+X2.sub.CET*DEN.sup.2+X3.sub.CET*DEN.sup.3+X4.sub.CET*TGAI+X5.sub.CET*TGAI.sup.2+X6.sub.CET*TGAI.sup.3+X7.sub.CET*DEN*TGAI=(3.4440824E+06)+(1.1648748E+07)(0.8828)+(1.2971167E+07)(0.8828).sup.2+(4.7663268E+06)(0.8828).sup.3+(3.4781476E+02)(372.8363)+(3.0996298E01)(372.8363).sup.2+(3.1335567E04)(372.8363).sup.3+(2.8259387E+02)(0.8828)(372.8363)=59
Pour Point.sub.GO(PP)=K.sub.PP+X1.sub.PP*DEN+X2.sub.PP*DEN.sup.2+X3.sub.PP*DEN.sup.3+X4.sub.PP*TGAI+X5.sub.PP*TGAI.sup.2+X6.sub.PP*TGAI.sup.3+X7.sub.PP*DEN*TGAI=(4.8586818E+06)+(1.6445177E+07)(0.8828)+(1.8314457E+07)(0.8828).sup.2+(6.7294243E+06)(0.8828).sup.3+(5.1784158E+02)(372.8363)+(4.9994583E01)(372.8363).sup.2+(5.0732788E04)(372.8363).sup.3+(4.0725036E+02)(0.8828)(372.8363)=10
Cloud Point.sub.GO(CP)=K.sub.CP+X1.sub.CP*DEN+X2.sub.CP*DEN.sup.2+X3.sub.CP*DEN.sup.3+X4.sub.CP*TGAI+X5.sub.CP*TGAI.sup.2+X6.sub.CP*TGAI.sup.3+X7.sub.CP*DEN*TGAI=(2.9180642E+05)+(9.9096539E+05)(0.8828)+(1.1102599E+06)(0.8828).sup.2+(4.1141986E+05)(0.8828).sup.3+(2.4644626E+01)(372.8363)+(2.4183985E02)(372.8363).sup.2+(2.4017172E05)(372.8363).sup.3+(1.9062052E+01)(0.8828)(372.8363)=11
Aniline Point.sub.GO(AP)=K.sub.AP+X1.sub.AP*DEN+X2.sub.AP*DEN.sup.2+X3.sub.AP*DEN.sup.3+X4.sub.AP*TGAI+X5.sub.AP*TGAI.sup.2+X6.sub.AP*TGAI.sup.3+X7.sub.AP*DEN*TGAI=(1.5741617E+06)+(5.3253923E+06)(0.8828)+(5.9279491E+06)(0.8828).sup.2+(2.1769469E+06)(0.8828).sup.3+(1.6833776E+02)(372.8363)+(1.6081980E01)(372.8363).sup.2+(1.6443813E04)(372.8363).sup.3+(1.3337068E+02)(0.8828)(372.8363)=66
Aromaticity.sub.WCO(AROM)=K.sub.AROM+X1.sub.AROM*DEN+X2.sub.AROM*DEN.sup.2+X3.sub.AROM*DEN.sup.3+X4.sub.AROM*TGAI+X5.sub.AROM*TGAI.sup.2+X6.sub.AROM*TGAI.sup.3+X7.sub.AROM*DEN*TGAI=(1.2131981E+05)+(4.1952545E+05)(0.8828)+(4.7011378E+05)(0.8828).sup.2+(1.7360561E+05)(0.8828).sup.3+(3.0649367E+01)(372.8363)+(6.2885397E02)(372.8363).sup.2+(6.4167386E05)(372.8363).sup.3+(1.1934777E+01)(0.8828)(372.8363)=18
Octane Number(ON)=K.sub.ON+X1.sub.ON*DEN+X2.sub.ON*DEN.sup.2+X3.sub.ON*DEN.sup.3+X4.sub.ON*TGAI+X5.sub.ON*TGAI.sup.2+X6.sub.ON*TGAI.sup.3+X7.sub.ON*DEN*TGAI=(3.1407161E+05)+(1.1079386E+06)(0.8828)+(1.2925048E+06)(0.8828).sup.2+(5.0229227E+05)(0.8828).sup.3+(2.1800822E+01)(372.8363)+(6.9721231E02)(372.8363).sup.2+(7.3440477E05)(372.8363).sup.3+(0)(0.8828)(372.8363)=55

(45) Accordingly, as shown in the above example, indicative properties including cetane number, pour point, cloud point, aniline point, and aromaticity can be assigned to the crude oil samples without fractionation/distillation (crude oil assays).

(46) In alternate embodiments, the present invention can be implemented as a computer program product for use with a computerized computing system. Those skilled in the art will readily appreciate that programs defining the functions of the present invention can be written in any appropriate programming language and delivered to a computer in any form, including but not limited to: (a) information permanently stored on non-writeable storage media (e.g., read-only memory devices such as ROMs or CD-ROM disks); (b) information alterably stored on writeable storage media (e.g., floppy disks and hard drives); and/or (c) information conveyed to a computer through communication media, such as a local area network, a telephone network, or a public network such as the Internet. When carrying computer readable instructions that implement the present invention methods, such computer readable media represent alternate embodiments of the present invention.

(47) As generally illustrated herein, the system embodiments can incorporate a variety of computer readable media that comprise a computer usable medium having computer readable code means embodied therein. One skilled in the art will recognize that the software associated with the various processes described can be embodied in a wide variety of computer accessible media from which the software is loaded and activated. Pursuant to In re Beauregard, 35 U.S.P.Q.2d 1383 (U.S. Pat. No. 5,710,578), the present invention contemplates and includes this type of computer readable media within the scope of the invention. In certain embodiments, pursuant to In re Nuijten, 500 F.3d 1346 (Fed. Cir. 2007) (U.S. patent application Ser. No. 09/211,928), the scope of the present claims is limited to computer readable media, wherein the media is both tangible and non-transitory.

(48) The system and method of the present invention have been described above and with reference to the attached figures; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.