GB2161269A - Determination of hydrocarbons in rock samples - Google Patents

Abstract

A method of determining quantitatively and qualitatively the hydrocarbons present in a sample in which the sample is pyrolyzed, the off stream split into two with one stream analyzed for total hydrocarbons present and the other stream passed through traps to separate the oil range hydrocarbons from the gas range hydrocarbons. Comparison of the gas range hydrocarbons to total hydrocarbons gives the amount of oil range hydrocarbons present. The trapped oil range hydrocarbons are then analyzed to give a "fingerprint" of the oil range hydrocarbons.

Description

SPECIFICATION Method of analyzing hydrogen and carbon containing materials This invention relates to the analysis of hydrogen and carbon containing materials.

The invention has a principal usefulness in the analysis of source rock and reservoir rock for petroleum and will be disclosed primarily in such field, although it is useful in any instance where it is desired to analyze a substance for its hydrogen and carbon containing compounds. For instance, any polymeric material may be analyzed. Specific examples of materials which might be analyzed are paints and plastics.

The petroleum industry utilizes sophisticated technology to explore for oil and gas. In frontier areas, geological studies are performed to evaluate the conditions most favorable for abundant hydrocarbon accumulations. The regional geology is assessed by methods which accurately define the areal distributions of reservoirs, traps, seals, and source rocks. Source rocks are evaluated by petroleum geochemical methods designed to identify the stratigraphy containing thermally mature, oilprone organic matter and responsible for sourcing commercial hydrocarbon accumulations.

The source rock evaluation is needed to plan the immediate exploration strategy in a frontier area.

Favorable source rock results will enhance the area 5 hydrocarbon potential and influence lease acquisition decisions. Frequently, the source rock geochemistry will be used with geophysical information to select the most favorable area for the next drilling location.

Previous methods for evaluating source rocks utilizing hydrocarbon evaluation required extensive laboratory facilities and analytical instrumentation.

A suite of analyses is performed on large amounts of rock samples by several highly trained chemical technicians. Results are usually not available for several weeks because the analytical process is time consuming and labor intensive.

The only known rapid process for rock sample analysis has compared hydrocarbons with oxygen containing compounds, such as CO2 in a sample, This is not believed to be as accurate as the present method which by direct analysis determines the oil range and gas range hydrocarbons present in a sample and the oil range and gas range hydrocarbons that can be obtained by pyrolysis of the rock after the petroleum products trapped in the rock have been evolved.

In the past, "fingerprints" of oil range hydrocarbons in a sample of source rock and reservoir rock have been obtained. These have been limited quantitatively, however, to the "fingerprint" of compounds containing up to about twenty-two carbon atoms. This is believed to be due to a lack of temperature control coupled with materials of the apparatus in contact with the evolved hydrocarbons. By this invention the quantitative "fingerprint" of a sample may be obtained including compounds having in excess of about forty carbon atoms.

The method of this invention provides for a rapid source rock assessment using pyrolysis and trapping techniques. In addition, quantitative data about oil and gas shows are obtained which can be used to identify possible production zones in reservoir quality rocks. Detailed "fingerprints" of oil and pyrolysis products are obtained for geological correlations by high resolution gas chromatography. Correlations of oil-to-oil, oil-to-source rock, and source rock-to-source rock are made by comparisons of the appropriate "fingerprints".

The high sensitivity of the analytical method permits quantitative oil and gas data and detailed "fingerprints" analysis to be performed on small amounts of rock ranging from 0.010 to 0.500 grams. Other geochemical methods such as solvent extraction and liquid chromatography require about 100 grams of material for routine analysis.

An object of this invention is to provide a method of analyzing a sample for hydrocarbons in which the total hydrocarbons and gas range hydrocarbons are directly obtained from a small sample in a short period of time.

Another object is to provide a method of analyzing a sample in which a "fingerprint" of the oil range hydrocarbons in the sample is obtained which "fingerprint" includes substantially all hydrocarbons in the sample.

Another object is to provide a method of analyzing a sample of source or reservoir rock by heating the sample to a temperature at which substantially all of the organic material in the sample is removed and total hydrocarbons and gas range hydrocarbons are directly measured from a small sample in a short period of time to provide for a determination of the oil range hydrocarbons by a direct comparison of total hydrocarbons to gas range hydrocarbons.

Another object is to provide a method as in the preceding object in which a "fingerprint" of the hydrocarbons contained within the sample, as well as a "fingerprint" of the hydrocarbons resulting from pyrolysis of the organic material in the sample are obtained in which substantially all of the hydrocarbons in the sample are included in the "fingerprint".

Another object is to analyze a sample for its hydrocarbon containing compounds in which the total of said compounds is compared to selected heavy molecular weight compounds.

Another object is to analyze a sample as in the preceding object in which the comparison is made at time-temperature intervals.

Other objects, features and advantages of the invention will be apparent from the drawings, the specification and the claims.

In the drawings wherein like reference numerals indicate like parts and wherein an illustrative embodiment of this invention is shown; Figure 1 is a schematic diagram of the equipment and flow therethrough during thermal extraction of the hydrocarbons contained within the sample; Figure 2 is a view similar to Figure 1 showing flow during pyrolysis of the parent kerogens of the sample; Figure 3 is a view similar to Figure 1 showing flow during "fingerprinting" of the oil range hydrocarbons from the sample; Figure 4 is a typical pyrogram plotting the gas and total hydrocarbons obtained during linear heating of the sample between ambient temperature and about 600" C from a reservoir rock sample; Figure 5 is a view similar to Figure 4 illustrating a typical pyrogram of the gas and total hydrocarbons obtained from a source rock;; Figure 6 is a "fingerprint" obtained from the hydrocarbon content of a reservoir rock; Figure 7 is a "fingerprint" obtained from the hydrocarbon content of a source rock; Figure 8 is a "fingerprint" obtained from the pyrolyzed kerogens from the source rock providing the "fingerprint" of Figure 7; and Figure 9 is a schematic illustration of the equipment preferred for use in carrying out the methods of this invention.

In practicing the method the solid sample is placed in the pyrolysis furnace. The furnace is preferably formed of fused quartz. An inert gas such as helium, is preferably used to sweep the evolved hydrocarbons out of the pyrolysis furnace. The fur nace is heated at a rate of about 40 Clmin or less, from ambient to about 600" C. Liquid samples may be introduced into the system by syringe injection into a heated injection port.

The stream from the furnace is split into two streams. One stream is connected to a flame ionization detector (FID). The electrometer voltage from the hydrocarbons ionized in the FID is measured by a sensitive voltage-to-frequency converter and transmitted to a computer for integration and data storage. The integrated peak areas are standardized by known amounts of hydrocarbons to yield the quantity of total hydrocarbons evolved during a specific time-temperature interval.

The hydrocarbons in the other stream are directed through a multiposition valve to successive traps, preferably formed of fused quartz. The traps consist of quartz tubes packed with fused quartz sand. The traps are maintained at about -60 C by liquid CO2. The liquid CO2 cools the trap by expansion into a quartz dewar which surrounds the quartz tubes. As the hydrocarbons pass through the traps, the oil range material (about nC6 and heavier) is retained. The gas range hydrocarbons (lighter than nC6) continue through the traps and the multiposition valve, to the FID where they are detected. The amount of gas evolved from the solid rock is measured in the same fashion as the total hydrocarbons.

The data acquisition system may calculate the amount of oil evolved from the rock by subtracting the gaseous hydrocarbons from the total hydrocar bons. Examples of the completed quantitative analysis are shown in the pyrograms for a typical source rock (Figure 5) and reservoir rock (Figure 4).

After the linear heating of the quartz furnace is completed, the carrier gas flow to the traps is reversed and the trap packing containing the heavy hydrocarbons is rapidly heated to about 350" C.

The heavy hydrocarbons are directed from the traps, through the multiposition valve to a collector and, preferably onto the liquid phase (methyl silicon polymer) of a fused silica capillary column located in an oven. Initially at about 50 C or less, the column is heated at about 10 Cumin by a linear temperature programmer to about 300 C. As the hydrocarbons are evolved from the column, they are measured by the data acquisition system to obtain a "fingerprint" of the oil. The "fingerprint" is plotted as a chromatogram similar to those shown in Figures 6, 7 and 8. Compounds such as n-paraffins, isoprenoid hydrocarbons, and for the pyrolysis products, alpha olefins are identified based on their retention times compared to external standards.

Reference is now made to the drawings to illustrate the practice of the method. Referring to Figure 1, the schematic flow diagram illustrates the equipment used and the setting of the valving dur ing thermal extraction of the sample in the furnace 10 to a temperature at which substantially all hydrocarbons which can be evolved by thermal expansion are evolved. The furnace 10 is preferably constructed of an inert material, such as fused quartz, which will not provide an active surface on which hydrocarbons are prone to collect. The furnace 10 is provided with a heating means capable of increasing the heat in the furnace at a linear rat up to about 600" C. The rate of heating is not critical but preferably is in the range of about 25 to 40G Clmin.

An inert gas, such as helium, argon, etc., is utilized to sweep the products of the pyrolysis furnace through the system. The gas is introduced through a flow controller 11 and the multi-positior valve 12 into the pyrolysis furnace 10 where it sweeps the hydrocarbons from the sample in the furnace as the hydrocarbons are released from tht sample. The sample may be any desired material as discussed hereinabove, and may be in solid or liquid from. Where cuttings or a core from a petrc leum well are analyzed, the pyrolysis furnace will first release all of the hydrocarbons contained within the sample by thermal extraction. During such thermal extraction the equipment will be uti- lized as indicated in Figure 1. The sweep gas pass ing through flow controller 11 travels through conduit 13 to the multi-position valve 12 and thence through conduit 14 to the pyrolysis furnace 10 where it picks up the thermally extracted hydro carbons. From the furnace 10 the sweep gas and hydrocarbons pass through conduit 15 to the multi-position valve 12 wherein they are split at 1 into two flow streams. One flow stream is fed through line 17 to the flame ionization detector 1E where the hydrocarbons in the stream are detects and the total amount of hydrocarbons being thermally extracted is determined.

The second split stream passes from the valve 12 through the conduit 19 to a two-way valve 21 and thence into the P, trap 22.

The P1 trap 22 is preferably a quartz tube packe with fused quartz sand. As in the case of the furnace 10, the trap should be constructed from an inert material, such as fused quartz, which will not provide an active surface. In the trap 22 the oil range hydrocarbons are trapped and retained and the gas range hydrocarbons are permitted to flow through the trap. Preferably, the oil range hydrocarbons are trapped by maintaining the trap at low temperature such as -60" C, but, of course, other types of traps which will separate the oil range from the gas range hydrocarbons may be utilized.

Preferably, the cut between oil range and gas range hydrocarbons is made at C6 and all C6 and greater weight hydrocarbons are retained in the P1 trap 22 while all gas range hydrocarbons of C6 and below pass through the trap. It will be understood, however, that the cut is not critical and may be varied at the desire of the operator. Normally, all C8 and heavier hydrocarbons are considered oil and would be trapped. All C4 and lighter hydrocarbons would be normally considered to be gas. The C8, C6, and C7 hydrocarbons are in the liquid condensate range and the cut will preferably be made anywhere in this range.

The gas passing through the P, trap 22 is conducted via conduit 23 to the multi-position valve 12 and thence through line 24 to the flame ionization detector 19 where its hydrocarbon content is determined. The information from the two flame ionization detectors 18 and 19 may be stored or may be fed to a suitable printer-plotter unit which will print the curves, such as shown in Figures 4 and 5 of the total hydrocarbons and gas range hydrocarbons being detected by the FIDs 18 and 19. The operation illustrated in Figure 1 is continued until substantially all of the hydrocarbons which may be extracted by thermal expansion have been extracted. This will normally occur at some point between about 320 C to 380" C.Substantially all of the thermally extracted material will have been generated by the time the temperature reaches 340" C. When the temperature reaches about 340" C, the valving is changed to direct the flow through the P2 trap 25. (See Figure 2) With the valving change a first split stream of the pyrolysis product continues to flow through the conduit 17 to the FID 18 so that the total hydrocarbon in the stream may be determined as the temperature in the pyrolysis unit continues to increase at a linear rate up to about 600" C. During this time the kerogens in the sample will be pyrolyzed into hydrocarbons and the FID 18 will determine the total hydrocarbons in the stream from the pyrolysis furnace 10.

The other stream passes through conduit 20 to the valve 30 and thence to P, trap 25. The P, trap 25 is preferably of the same construction as the P1 trap 22 and is operated in the same manner to trap the oil range hydrocarbons while permitting the gas range hydrocarbons to pass through the trap and conduit 26 to the multi-position valve 12. From the valve 12 the gas range hydrocarbons are directed through line 24 to the FID 19 where the hydrocarbons in the stream are detected.

After pyrolysis is complete the control valves are positioned as shown in Figure 3 and the "fingerprint" of the oil range hydrocarbons contained within the P, trap 22 and the P, trap 25 are detected to determine the "fingerprint" of the trapped oil range hydrocarbons.

The flow controller 11 now provides through the valve 12 make up gas through lines 17 and 24 to the two FIDs 18 and 19. The valve 21 is switched to receive sweep gas from flow control 27 through the valve 12 and line 28. The P, trap, in like manner, receives sweep gas from flow control 29 through valve 12 conduit 31 and valve 30.

Each of the P, trap and the P, trap is now heated rapidly from its condensing temperature of preferably -60" C to about 350 C. For instance, the trap may be heated at a rate of 200 C per minute.

Again, the rate of heating is not critical but should be rapid. The above rate is given by way of example. During heating all of the hydrocarbons contained within the two traps will be released. The hydrocarbons in the P, trap will be swept by the sweep gas from line 28 through line 32 to the collector 33. In like manner, the hydrocarbons from the P, trap 25 now pass through the valve 30 to the line 34 and thence to the collector 35.

If desired, the valves 21 and 30 may be so constructed that with the valves 21 and 30 set in the manner shown in Figures 1 and 2 the sweep gas from the flow controllers 27 and 29 will pass through the valves 21 and 30 to the FIDs 18 and 19. This will permit the flow controllers 27 and 29 to maintain stable gas flow through the system.

If desired, splitters 36 and 37 may be provided upstream of the collectors 33 and 35 to split off a portion of the stream from the traps 22 and 25, respectively.

While any type of collector 33-35 may be utilized, where high resolution is desired, it is preferred to utilize a fused quartz capillary column having a liquid phase, such as methyl silicon polymer.

Prior to the time that the P, and P, traps are heated to drive off the oil phase hydrocarbons, the two columns 33 and 35 will be at ambient temperature.

After the traps are heated and the heavy hydrocarbons collected in the capillary tubes 33 and 35, the two tubes are heated at a suitable linear rate, such as 10 C/min to a maximum temperature of about 300 C to progressively release the hydrocarbons which are detected in the two FIDs 18 and 19 to provide in the conventional manner a "fingerprint" of the oil range hydrocarbons.

Reference is now made to Figure 9 in which a preferred from of apparatus for carrying out the method is illustrated.

In the past oil range hydrocarbons have been trapped and then collected in capillary tubes and recovered and detected in flame ionization detectors. The heaviest hydrocarbon which it has been possible to detect quantitatively in the past has been about C22. By reference to Figures 6, 7 and 8 which are "fingerprints" obtained utilizing the method disclosed herein, it will be seen that this method quantitatively detects hydrocarbons in the plus C40 range.

The detection of substantially all of the heavier hydrocarbons is made possible by the use of inert material, such as fused quartz in the heater, the traps and the capillary tubes combined with control of the temperature of the flowing streams when they are not contained within quartz equipment.

In accordance with this invention a temperature controlled block, indicated generally at 38, is provided and all of the valving, as indicated at 39, and conduits are contained within this block 38. The pyrolysis furnace 10, the traps 22 and 25, and the capillary columns 33 and 35 are connected to tubing within the block 38 and only a very short length of connector is exposed exterior of the block to permit making these connections. Preferably, the connections are limited to about a quarter of an inch between the block and the connected piece of equipment, such as the pyrolysis unit 10.

The temperature within the block 38 is maintained at a sufficiently high level to prevent the heavier hydrocarbons depositing out on the valving conductors and the like within the block 38. On the other hand, the temperature is below the level at which pyrolysis of the hydrocarbons in the system would occur. Preferably, the block 38 is maintained at least at about 300' C and no more than about 400 C. Preferably, the block 38 is maintained at approximately 350' C.

The FID 41 may be partly contained within the block 38 or connected thereto in a means that minimizes exposure of the connecting conduit. Preferably the external connectors to the block 38 have such minimum area of exposure that the heavy hydrocarbons passing therethrough will be maintained above about 300 C.

The data from the flame ionization detector 41 is fed to the converter 42 and thence to the computer 43 and the printer-plotter unit 44.

In Figure 4 there is shown a pyrogram from a sample of reservoir rock charting the gas analysis from the FID 19. This results in the ascending curve 42 and the descending curve 43 during thermal extraction and the ascending curve 44 and the descending curve 45 during pyrolyzing of the kerogens. The total hydrocarbons are reflected in the curve 46. For the ascending curve 42 and the first portion of the descending curve 43 the gas range hydrocarbons and the total hydrocarbons are the same. Thus, the method of this invention may be utilized to determine the relative amounts of oil and gas in the total hydrocarbons within a reservoir rock. This may be correlated with "fingerprints" from the reservoir rocks to indicate the type of oil present.

A source rock pyrogram is shown in Figure 5.

Here the ascending gas curve 47 and the descending gas curve 48, as well as the high temperature ascending gas curve 49 and descending gas curve 50 indicates the amount of gas extracted during thermal extraction and during pyrolyzing of the kerogens. The total hydrocarbon curve 51 may be compared to the gas curves to indicate the amount of oil range hydrocarbons in the source rock.

While the pyrograms of Figure 4 and Figure 5 are illustrative and do not represent a particular sample, the "fingerprints" of Figures 6, 7 and 8 are actual "fingerprints" from samples. Figure 6 is an actual "fingerprint" of a sample of reservoir rock from the trap P, plotting millivolts against time ane showing the carbon numbers at selected chart peaks.

Figures 7 and 8 are actual "fingerprints" of a sample of source rock and showing in Figure 7 the thermally extracted "fingerprint" from the trap P, and in Figure 8 the "fingerprint" of the pyrolyzed kerogens from trap P,. Again, time is plotted against millivolts and the carbon weight indicated at appropriate peaks.

In obtaining these "fingerprints", the temperature controlled heater block 38 of Figure 9 was pro vided by surrounding conduits between functioning elements and valves with heated jackets and by placing appropriate equipment within furnaces so that, as indicated by the temperature controlled heater block 38, substantially all of the system was either quartz or was maintained at approximately 350 C. This permitted the fine resolution and finger printing of the oil range hydrocarbons up to carbons in excess of 40, as shown on the "fingerprints".

If desired, a plurality of traps could be substituted for each of the traps P, and/or P,. Thus the first P, trap might trap C,, hydrocarbons and per mit C,-C,, to pass through to a second P, trap. This second trap might retain C,-C,,, and pass C,-C6. A third trap might retain Cs-C6 and pass Cl-C4. Finally a fourth trap might retain C,-C4 and pass C,. The several traps would be successively flushed to the collector and then separately "fingerprinted".

As an alternative, a pluralty of P, and/or P, traps could be used to trap C6+ hydrocarbons evolved C specific time-temperature intervals to determine the amount of C, -C6 and C6+ hydrocarbons evolve at each interval. Thus, at intervals of say 100" C th hydrocarbons evolved might be directed to separate traps. Thus, the first P, trap would retain C6+ hydrocarbons and pass C,-C6. At 100" C the evolving stream would be directed to a second P, trap and so on. The traps would be separately analyze in the manner explained above to obtain data related to each time-temperature interval.

A still further analysis could be made by combii ing the last two analyses. Thus, hydrocarbons evolved during a particular time-temperature inte val might be passed successively through a series of traps to separate C,,, C7-C,,, C6-C6, C,-C4, C, which could be analyzed as described above.

These analyses would perform a simulated dist lation for boiling point distribution, and determine the composition of each boiling point fraction.

They would yield data on the energy required to degrade solid organic materials, such as polymer: for example polyethylene, and determine the corr position of the thermal degradation products.

The methods disclosed herein may be used to analyze materials in which the hydrocarbons are the major portion of compounds which may be evolved from a sample by pyrolysis.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention.

Claims (9)

1. An apparatus for analyzing hydrocarbon-containing samples comprising: means to provide a heated zone at a temperature of from about 300 to about 400 C; fused quartz multi-position valving means disposed within said heated zone; fused quartz pyrolysis furnace; first fused quartz conduit means interconnecting said fused quartz pyrolysis furnace and said valving means; means to maintain a gaseous medium flowing in said first conduit means at a temperature of at least about 300 C; at least one fused quartz trap means; means to selectively heat said one trap means to a temperature of at least about 300"C; second fused quartz conduit means interconnecting said one trap means and said valving means;; means to maintain a gaseous medium flowing in said second conduit means at a temperature of at least about 300"C; detector means; third fused quartz conduit means interconnecting said detector means and said valving means; and means to maintain a gaseous medium flowing in said third conduit means at a temperature of at least about 300"C; said valving means being operative to provide selective, fluid flow interconnection between said pyrolysis furnace, said one trap means and said detector means.

2. The apparatus of Claim 1. including a second fused quartz trap means, means to selectively heat said second trap means to a temperature of at least about 300"C, fourth fused quartz conduit means interconnecting said second fused quartz trap means and said valving means and means to maintain a gaseous medium flowing in said fourth conduit means to a temperature of at least about 300"C.

3. The apparatus of Claim 1. including at least one fused quartz capillary column separating means, means to heat said one column separating means to a temperature of about 300"C, fifth fused quartz conduit means interconnecting said one column means and said valving means and means to maintain a gaseous medium flowing in said fifth conduit means to a temperature of at least about 300"C.

4. The apparatus of Claim 3. including a second fused quartz capillary column separating means, means to heat said second column separating means to a temperature of about 300"C, sixth fused quartz conduit means interconnecting said second column means and said valving means and means to maintain a gaseous medium flowing in said sixth conduit means to a temperature of at least about 300 C.

5. The apparatus of Claim 1. including means to flow an inert gaseous medium through said valving means, said pyrolysis furnace, said trap means and said detector means.

6. The apparatus of Claim 1. including means to heat said pyrolysis furnace.

7. The apparatus of Claim 6. wherein said means to heat said pyrolysis furnace include means to heat said furnace at a rate of about 40 C/ min or less in a temperature range of from about ambient to about 600"C.

8. The apparatus of Claim 6. including means for selectively cooling and heating said trap means.

9. The apparatus of Claim 1. wherein said detector means comprises a flame ionization detector.