Abstract:
A method for analyzing total oil in place and fraction that is movable oil in a fine gain rock formation includes monitoring thermal extraction of hydrocarbon and non-hydrocarbon compounds from a sample of a subsurface formation by heating the sample. The heating has a selected initial temperature, and a temperature increase at a selected rate to a final temperature. The extracted hydrocarbon and non-hydrocarbon compounds are passed through a capillary column to a flame ionization detector. Types of hydrocarbon and non-hydrocarbon compounds and relative fractional amounts of each type thereof are determined from the sample by analyzing a chemical thermogram generated by the flame ionization detector.

Description:
BACKGROUND 
       [0001]    This disclosure is related to the field of analysis of extracted oil from samples of subsurface formations withdrawn from wells drilled through such formations. More specifically, the disclosure relates to methods for performing tests on such samples to quantify the total oil in place and which fraction of the in place oil is movable in such formations. 
         [0002]    Oil-in-place (OIP) and movable oil (MO) analysis of subsurface formations traversed by a wellbore has been carried out with petrophysical analysis (analysis of measurements of selected physical properties made by sensors disposed in a wellbore) and some limited geochemical measurements of formation samples withdrawn from wellbores (e.g., programmed pyrolysis). Some studies suggest that programmed pyrolysis S1 (free hydrocarbon measurement) could be used to evaluate direct measurements of inplace oil in such formations. One major petroleum producing company has developed a pyrolytic method to quantitatively assess reservoir quality from residual oil staining on drill cuttings in real time (Jones et al. 2007,  Implementation of Geochemical Technology for real Time Tar Assessment and Geosteering: Saudi Arabia ). Another major petroleum producing company has developed a proprietary programmed pyrolysis S1 OIP analysis (Michels et al., 2013,  Determination of in - situ hydrocarbon volumes in liquid rich shale plays,  URTec meeting paper). The foregoing method uses analysis programs known by the trademark ROCK-EVAL which is a registered trademark of IFP Energies Corporation, 1 et 4, avenue du Bois-Preau 92 Rueil-Malmaison, Cedex 92852, France and the trademark SRA, which is a trademark of Weatherford International plc, 2000 St. James Place, Houston, Tex. 77056. to perform programmed pyrolysis in conjunction with a process to correct S1 using produced fluids from nearby wellbores. Both of the foregoing methods use standard programmed pyrolysis. 
       SUMMARY 
       [0003]    A method for analyzing in place movable oil in a fine grain rock formation according to one aspect includes extracting oil from a sample of a subsurface formation by heating the sample and evaluating its mobility components. The heating has a selected initial temperature, and a temperature increase at a selected rate to a final temperature. The thermally extracted oil is passed through a short uncoated capillary column to a flame ionization detector. Types of hydrocarbon and non-hydrocarbon compounds as well as fractional amounts of each type thereof are determined from the sample by analyzing a chemical thermogram generated by the flame ionization detector. 
         [0004]    Other aspects and advantages will be apparent from the description an claims that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  shows an example apparatus for carrying out analysis according to the present disclosure. 
           [0006]      FIG. 2  shows an example form of chemical thermogram that may be generated by a thermal extraction with short uncoated capillary column and flame ionization detector. 
           [0007]      FIG. 3  shows an example chemical thermogram having four peaks. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    In methods according to the present disclosure, a multi-step, high resolution thermal extraction/short uncoated column-flame ionization detector (MSHRTE/SUC-FID) may be used to sequentially liberate in-situ hydrocarbon and non-hydrocarbon oil components from specially collected and processed conventional-side wall core and/or drill cutting rock material. The MSHRTE procedures may use a low starting temperature, fixed isotherm period, unique ramp rate, and ending temperature below that at which kerogen or oil cracking may occur to characterize a full range of in-situ oil component groups (e.g., straight chain alkanes, branched alkanes, naphthenes, aromatics, heteroatoms-NSO, and asphaltenes). The MSHRTE is coupled to a flame ionization detector (FID) by a short, uncoated capillary column to generate additional separation in the thermal extraction profile (thermogram). The MSHRTE/SUC-FID thermogram signature (peak shape, area, and height) is examined for each key thermal fraction. A mobility ratio may be calculated and then calibrated for each formation. 
         [0009]      FIG. 1  shows an example apparatus that may be used in some embodiments. A high resolution thermal extractor (HRTE)  10  may be used to sequentially liberate in-situ hydrocarbon components from specially collected and processed fine grain rock samples  11  to minimize volatile hydrocarbon loss prior to analysis. An example HRTE  10  is sold by CDS Analytical, Inc. 465 Limestone Road, P.O. Box 277, Oxford, Pa. 19363-0277 under the model designation ACEM 9300 Series. Formation samples  11  from a subsurface formation or other sample of rock to be evaluated may be processed in the HRTE  10  as will be further explained below. 
         [0010]    The HRTE  10  may be coupled to a flame ionization detector (FID)  14  by a short, uncoated capillary column  12 . The column  12  may be a short length (1.0 m) of deactivated, uncoated fused silica (commonly referred to as a guard column). This uncoated column  12  will have a typical internal diameter of 0.10 mm. Such connection may generate additional hydrocarbon and non-hydrocarbon character separation in the thermal extraction profile (chemical thermogram). The FID  14  generates a chemical thermogram, as shown at  16  in  FIG. 2 . The character (peak shape, distribution, and height) and maximum temperature response in the chemical thermogram  16  may be calibrated for each identified hydrocarbon fraction using samples of known composition subjected to analysis in the FID  14  to estimate total oil in place in the subsurface formation and the fraction of the foregoing that is movable oil. 
         [0011]    One or more samples of a subsurface formation may be obtained such as by extraction of a sidewall (percussion or drilled) core sample, a whole core (drilled, e.g., using an annular core drill bit) or by collection of drill cuttings returned to the surface from a wellbore during drilling. The one or more samples of rock material may sub-sampled, e.g., by depth interval or other sample segregation procedure. The one or more samples may be immediately wrapped in non-coated metal foil so as to minimize losses of volatile hydrocarbons. The wrapped samples of rock material may be placed in a pressure-sealed storage container and kept at reduced temperature conditions (approximately 2° C.) until processing according to the present disclosure. 
         [0012]    The rock material samples may be initially processed by removal of contaminants and then grinding the rock material into a fine powder. The sequential thermal extraction may be performed using a modified thermal extraction unit. A quartz tube  15  is filled with a selected size sample of the rock material powder (20 milligrams in the present example). The quartz tube  15  may be protected at both ends with quartz wool  13 . The quartz tube  15  with a set volume of powdered rock sample is placed in a probe (not shown separately). The probe is then inserted in the HRTE  10  where an optimized heater interface temperature program is used for the sequential thermal extraction program. The HRTE  10  may be operated by heating to a first temperature and holding the first temperature for a selected time. In some embodiments, the first temperature may be followed by increasing the temperature at a selected rate and holding the second temperature for a selected time. In other embodiments, holding the second temperature may be followed by subsequent increases in temperature at a selected rate followed by holding temperature at one or more additional higher temperatures for selected times until a final selected temperature is reached and held for a selected time. The HRTE  10  initial temperature in the present example embodiment is 200° C. held for 15 minutes. The initial temperature may followed by a temperature increase (ramp) of 60° C./minute until the temperature reaches a second temperature, in the present example 250° C., which is held for 15 minutes. Subsequently, the temperature of the HRTE  10  may be increased in successive ramps of 60° C./min and held for 15 minutes each at 300° C. for and 350° C. 
         [0013]    At the same time, operation of the short uncoated column (SUC) flame ionization detector (FID)  14  is started. The FID  14  is coupled to the HRTE  10  using a deactivated, uncoated capillary column  12  having dimensions in the present example of 1 meter length, 0.25 millimeter internal diameter and wall thickness of about 75 micrometers. The SUC oven temperature was operated to maintain 300° C. for 65 minutes. Description of such an oven may be found in “Model 6890N Gas Chromatograph, User Information”, Part No. G1530-90210, Agilent Technologies, 5301 Stevens Creek Blvd, Santa Clara, Calif. 95051 (May 2001). An injector was operated in split mode (10:1) at a 270° C. The injector may be one sold by Agilent Technologies under model designation “7890/6890/6850 Split/Splitless Inlet.” 
         [0014]    The foregoing multiple temperature, high resolution thermal extraction generates a chemical thermogram with four major peaks as shown in  FIG. 3 : 
         [0015]    Peak 1: P 200° C.  shown at  18   
         [0016]    Peak 2: P 250° C.  shown at  20 . 
         [0017]    Peak 3: P 300° C.  shown at  22   
         [0018]    Peak 4: P 350° C.  shown at  24   
         [0019]    The area underneath each peak (P1, P2, P3, and P4) using a defined baseline is quantified. Several MSHRTE Mobility Ratios may be calculated using the area under each peak P1, P2, P3, and P4 as shown below: 
         [0020]    MSHRTE Mobility Ratio 1: P1 200° C. /P3 300° C. +P4 350° C.    
         [0021]    MSHRTE Mobility Ratio 2: P1 200° C. /P1 200° C. +P3 300° C. +P4 350° C.    
         [0022]    MSHRTE Mobility Ratio 3: P1 200° C. +P2 250° C. /P3 300° C. +P4 350 ° C.    
         [0023]    The MSHRTE Mobility Ratios are calibrated to each prospective liquid rich resource target. The MSHRTE Mobility Ratios may be examined to evaluate the likely production from specific formation zones for horizontal well location with other important parameters and identify the more prospective zones for fracking stages (specific zones are injected with special fluid and proppant at a high pressure in order to induce in situ fractures to enhance production). 
         [0024]    Specific compound identification can be achieved by coupling the MSHRTE to a conventional whole oil gas chromatograph wherein key compounds are quantified. Selected compounds are chosen based on their mobility to undertake a compound specific mobility ratio. Examples of selected calibration compounds are shown in TABLE 1. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Hydrocarbons 
                 Target Compounds Ratio 
                 Movability 
               
               
                   
                   
               
             
             
               
                   
                 Aromatics 
                 Methyl-perylene/dimethyl 
                 Less movable/ 
               
               
                   
                   
                 phenanthrene ratio 
                 movable 
               
               
                   
                 Aliphatics 
                 Heptacosane/tetradecane 
                 Less movable/ 
               
               
                   
                   
                 ratio 
                 movable 
               
               
                   
                   
                 Heptacosane ratio 
                 Non movable/less 
               
               
                   
                   
                   
                 movable 
               
               
                   
                   
               
             
          
         
       
     
         [0025]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.