Lawrence Livermore National Laboratory (LLNL) is currently involved in a long term study using time-lapse multiple frequency electromagnetic (EM) characterization at a waterflood enhanced oil recovery (EOR) site in California operated by Chevron Heavy Oil Division in Lost Hills, California (Figure 1). The petroleum industry's interest and the successful imaging results from this project suggest that this technique be extended to monitor CO{sub 2} sequestration at an EOR site also operated by Chevron. The impetus for this study is to develop the ability to image subsurface injected CO{sub 2} during EOR processes while simultaneously discriminating between pre-existing petroleum and water deposits. The goals of this study are to combine laboratory and field methods to image a pilot CO{sub 2} sequestration EOR site using the cross-borehole EM technique, improve the inversion process in CO{sub 2} studies by coupling results with petrophysical laboratory measurements, and focus on new gas interpretation techniques. In this study we primarily focus on how joint field and laboratory results can provide information on subsurface CO{sub 2} detection, CO{sub 2} migration tracking, and displacement of petroleum and water over time. This study directly addresses national energy issues in two ways: (1) the development of field and laboratory techniques to improve in-situ analysis of oil and gas enhanced recovery operations and, (2) this research provides a tool for in-situ analysis of CO{sub 2} sequestration, an international technical issue of growing importance

Kirkendall, B.

Roberts, J.

UNT Digital Library

Preprint UCRL-JC-142753 US. Department of Energy Electromagnetic Imaging of CO, Sequestration at an Enhanced Oil Recovery Site B. Kirkendall and J. Roberts This  article was submitted to First  National  Conference on Carbon  Sequestration,  Washington, D.C., May 14-17,2001 February 28,2001 Approved for public release; further dissemination unlimited  DISCLAIMER  This document was prepared as an account of work sponsored by an agency of the United StatesGovernment.  Neither the United States Government nor the University of California nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately owned rights. Reference herein to any specificcommercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does notnecessarily constitute or imply its endorsement, recommendation, or favoring by the United StatesGovernment or the University of California.  The views and opinions of authors expressed herein do notnecessarily state or reflect those of the United States Government or the University of California, andshall not be used for advertising or product endorsement purposes.  This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may bemade before publication, this preprint is made available with the understanding that it will not be citedor reproduced without the permission of the author.   This report has been reproduced directly from the best available copy.  Available electronically at     http://www.doc.gov/bridge    Available for a processing fee to U.S. Department of Energy And its contractors in paper from U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 Telephone:  (865) 576-8401 Facsimile:  (865) 576-5728 E-mail:   reports@adonis.osti.gov    Available for the sale to the public from U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone:  (800) 553-6847 Facsimile:  (703) 605-6900 E-mail:   orders@ntis.fedworld.gov     Online ordering:     http://www.ntis.gov/ordering.htm       OR  Lawrence Livermore National Laboratory Technical Information Department’s Digital Library http://www.llnl.gov/tid/Library.html  Electromagnetic  Imaging of C02 Sequestration at: an Enhanced Oil Recovery Site Barry Kirkendall (Kirkendall l@llnl.gov ; 925-423-1 5 13) Jeff Roberts (Robertsl7@llnl.gov ; 925-422-7108) Lawrence  Livermore  National  Laboratory 7000 East Avenue Livennore, CA 94550 1.1 Introduction Lawrence  Livermore  National  Laboratory  (LLNL) is currently  involved in a long term study using time-lapse  multiple frequency electromagnetic (EM) characterization  at  a  waterflood  enhanced oil recovery (EOR) site in California operated by Chevron Heavy Oil Division in Lost Hills, California (Figure 1). The petroleum industry's interest and the successll imaging  results  from t h i s  project suggest  that t h i s  technique be - extended to monitor COz sequestration at an EOR site also operated by Chevron.  The  impetus for this study is to develop the ability to image  subsurface  injected C 0 2  during EOR processes while simultaneously discriminating  between  pre-existing  petroleum  and water deposits.  The  goals of this study are  to  combine laboratory and field  methods to image  a pilot COz sequestration EOR site using the  cross-borehole EM technique,  improve the inversion process in COz studies by coupling results with petrophysical  laboratory 123"W 122'W 121W 120W It9 'W 118'W 117'W 38"M 37'N 33"N 3S'N 34"N 33"N 38'N 37'N 36"N 35" 34"N 33"N 123"W 122OW 121"W I2O"W 119"W 1 IS'W 117"W measurements, and focus  on new gas  interpretation techniques. In this  study we primarily focus on how joint field and laboratory results can provide information on subsurface COz detection, C02 migration tracking, and displacement of petroleum and water over time.  This  study directly  addresses  national energy  issues in two ways: 1) the development of field and laboratory  techniques to improve in-situ analysis of oil and gas enhanced  recovery operations and, 2) this  research provides a tool for in-situ analysis of COZ sequestration, an international  technical  issue of growing  importance. Figure 1. Map showing the location of the Lost Hills Oil Fields in California 1.2 Objective We are attempting to develop a technique for monitoring  in-situ C02 sequestration.  The initial task  is to  develop EM methods  to  image COZ sequestration in a petroleum  environment.  Subsequent tasks include developing  permanent sensors to  monitor C02 sequestrated reservoirs and  extending this technique to three- dimensional  single-well  imaging and cross-well  imaging  though steel casing. 1.3 Approach Previously a waterflood site, the  proposed C02 injection location has typically produced a lower petroleum  yield than expected during  primary and secondary recovery  operations.  While C02 injection  for EOR provides the advantage of  higher  production  yields and viscosity  reduction in heavy  oil,  it has the disadvantage  of increased cost; sequestration of industrially  produced C02 can significantly offset such  cost increases.  The oil industry is therefore  interested in a long-term study into the feasibility of C02 injection for the purposes of carbon sequestration and  subsurface  petroleum  mobilization  with  the  eventual possibility of running a gas pipeline to injection boreholes if such processes prove  economically  viable.  Initially, two observation  boreholes  have  been  drilled by Chevron USA, core and fluid samples were  made available to LLNL, and,  because of the highly  corrosive COz environment, two of the four pre-existing  injection  boreholes have  also  been redrilled and electrically  characterized.  Chevron  began  injecting C02 into the  mature waterflood site in December 2000 and reached  full  injection pressure in February 2001. This opportunity to image a carbon sequestration EOR site is  unique  because it provides a highly  controlled  and characterized subsurface through a pre-injection  deployment o acquire a baseline image and unrestricted access to  the observation  boreholes. A pre-sequestration  baseline data was acquired in August, 2000 which  will allow time- lapse  imaging after the June 2001  deployment. 1.4 Project  Description 1.4.1 Laboratory ApDroach We propose to measure  the  electrical properties of samples  from  the site at conditions of full liquid saturation  with  oil  and as they are invaded  with  liquid and gaseous C02. Measurements  will  be  performed at temperatures and pressures appropriate  to field conditions in a specially constructed  device specifically aimed at  these  types of measurements.  The  system  (Figure  2) consists of an externally heated fluid pressure vessel capable of confining pressures up to 10 MPa and temperatures up  to 300°C. Pressure is  controlled  by three different  pressure systems-ne each for confining pressure and upstream and downstream  pore  pressure control.  Electrical  measurements  will be performed  using two systems, a Hewlett-Packard  HP4282  impedance bridge and a Solartron 1260 impedance  analyzer.  The HP4284 is used  to  monitor the sample at specific frequencies during periods of heating,  pressure  changes, and fluid  injection.  The  impedance  analyzer is used to make broadband  measurements  during ( to lo6 Hz) periods  when  the  sample is at stable  experimental conditions.  The  device and measurement  methodology has been tested on  oil-filled  diatomite  samples from the Lost  Hills  that  were injected with brine  during EOR (Figure 3). These  preliminary  measurements  showed some  unexpected electrical behavior,  resistivity increasing during  brine  injection, that helped interpret the Chevron  well-logs and the LLNL crosswell  inversions. The  experimental  method  will be adapted for the COa injection  process. A well-characterized  water- or oil-saturated  sample  will be placed in the vessel for electrical measurements at the temperature of the formation (-38-45 C) and a variety of confining  and  pore pressures. Then,  liquid C02 will be forced into the sample and the electrical properties monitored as the liquid water is pushed  out. This will be easily accomplished at room  temperature,  as the critical pressure for COz at 3 1 'C is 72.8 atm or -7.3 MPa (CRC, 1983), well  within  the operating parameters of the  device. Changes in the electrical properties will be noted. Next the pore pressure will be lowered so that the liquid C02 flashes to the gas phase. The electrical properties will  be  again  be  monitored  for  a  period of time as the  sample  is  held at static conditions  to  determine  if  there  is a  long-term  effect. It is important  that there is some  knowledge  of surface conduction  mechanisms  in  the  rocks so that any changes in electrical properties  because  of  different surface tensions and wetting  behavior  can  be discerned and understood. A  second type of experiment  involves  the  injection of gaseous COz. As  above,  electrical  properties will be monitored as the sample undergoes  invasion of COz. It  may be necessary to pump to relatively  high pressures to obtain displacement  of  water. We will  attempt to match  reservoir  characteristics  whenever possible. Samples undergoing  boiling or C02 invasion  may  change  geochemically.  The  nature  of  the geochemical change will be dependent  on  a  number of factors,  including  rock  chemistry,  temperature, pressure, waterhock ratios, and fluid  chemistry.  These  changes can affect measured  electrical  properties,  in particular the surface  conductance.  Care  will  be  taken to be  aware of such changes  and  their  importance to observed  geophysical  measurements.  When  necessary, our analyses  will  include  a  geochemical  component. 1.4.2 Field  Approach Electromagnetic techniques are sensitive to rock  pore  fluids  within  the  subsurface,  which  makes  them the  ideal  method for addressing the  problems  of EOR in  a  heavy  oil  environment. In EOR applications,  it is also important  to discern between  injection  steam and gases,  injection  fluids, and formation  fluids.  The  high sensitivity of electromagnetic  energy to these  physical  processes, as well as recent  advances in computational ability,  inversion code resolution, and  field  instrumentation,  make  borehole EM techniques an important  tool for  such  subsurface  imaging  problems. During COz sequestration, the  high  pressure of the injection forces the C02 to  remain in a  liquid  state. AAer delivery to the subsurface formation,  however,  a  volume  increase  creates  a  pressure  drop  which vaporizes the C02 to a gaseous state.  It is this  gaseous state that forces miscibility  with  the  water  and oil in  the subsurface formation. secondary  recovery, and the original  liquid  petroleum  in  the  formation.  Based  on initial forward  model calculations,  we expect a  large  contrast  between  the  formation  water nd the  petroleum / C02, but a  small contrast  between the C02 and the  petroleum  due  to  the  similar  inherent  electrical  conductivities of ach component,  Resolution  of this small  contrast  will  be  possible with laboratory  results  and  with  improved gas interpretation techniques which  will  be  developed  based  on  higher  resolution  inversion  techniques. Results  of subsurface imaging  in the 2-D plane  between  the  boreholes  will  appear  similar to Figure 4, an inverted  conductivity  image fiom a  tomographic data set with a source frequency of 2.0 kHz. The  image  in Figure 4 clearly shows the location of the injected electrically conductive  water (blue) and  the  pre-existing resistive  petroleum deposits (red).  The  significance  of jointly conducting  laboratory  and  field  results can be seen  when  Figure 4 is interpreted with the petrophysical  results  of  Figure 3. Initially, the lowest  injector in Figure 4 does  not appear to have  infiltrated  the  formation  due to the large resistive body  at 1650 ft depth. Figure 3, however, demonstrates that  we  should  expect  a sharp rise in resistivity at the  onset  of  waterflooding, which  will  eventually lower over increased  time.  Therefore,  Figure 4 suggests  that  injection  fluid  at 1650 ft depth has only  recently  penetrated  into  the  formation. We expect  this  resistive  signature  to  lower  over increased  time, as shown in laboratory  results. entire CO2 injection interval, approximately 1500 ft - 1800 R. The  proposed  observation  boreholes are separated  by  approximately 30 meters,  with  one of four C02 injectors  directly  between  the  boreholes. Electrical conductivity snapshot images such as Figure 4 will  be acquired every  six  months for multiple frequencies  which  will allow the tracking of COz, petroleum,  and  water  over  increased  time. In this  complex scenario, EM imaging  must address the  gaseous C02, the liquid  water  leftover &om Proposed  tomographic data sets  will  include 2.0 kHz  and 4.0 kHz source frequencies  and span the 1.5 Results In  August 2000, LLNL  acquired  pre-sequestration  baseline  data  which  is  currently  being  processed  to produce  a  two-dimensional  tomographic  image  such as seen  in  Figure 4. In order  to  do  this we first  need  to correct  for  well  deviation  which  is  significant  at  this  site  (Figure 5) .  In  April  2001,  LLNL is  acquiring  a second  dataset  which  can  be  inverted  to  an  image  and  compared  to  the  baseline  image.  We  are  in  the  process of  building  and  calibrating  our  petrophysical  laboratory  apparatus  (Figure 3) to  accept  the  core  samples  and formation  and  C02  injection  fluids. We  expect to show  preliminary  imaging  and  laboratory  results  at  the  May conference. 1.6 Application and Benefits The  real  benefit of imaging COZ sequestration is determining  the  location  and  spatial  extent  of  the  injectate  in the  subsurface. Subsdace fractures  and  micro-tunneling  caused  by  C02  injectate  provide  alternate  subsurface pathways  which  often  produce  both  legal nd environmental  problems. In California,  several  new  power plants which  were  recently  commissioned  are  sited  in  the  San  Joaquin  Valley, California  which  are  close  to  the  location  of  heavy  oil  production.  The COz output of the  power  factories would be able  to be directly  and  cheaply  injected  into  the  subsurface  to  assist  in EOR. This  technique  could  be used  to  actively  image  the COz during  initial  sequestration  and  then  extended,  by  employing  permanent sensors,  for  longer  term  reservoir  monitoring. 1.7 Future Activities This  study  will  continue  for  another 18 months,  where  LLNL  will  continue  to  monitor  the COz sequestration and  run  core  sample / COz experiments  in  the  laboratory.  We  will  next  focus  on  inversion  optimization techniques in order  to  help  accentuate  the  small  electrical  conductivity  contrast  between  sequestrated C02 and formation  fluid  (oil  sands).  Additionally,  we  will  focus  on  developing  field  techniques  to  lower  the  noise  floor in data  acquisition. 1.8 Acknowledgements The  authors  would  like to thank  Mike  Morea  at  Chevron  for  providing  access  to  the  wells  in  addition  to tangible  welt  information  such as gyroscopic dab and  induction  logs. We would  also  like to thank  Steve Carlson,  Pat  Lewis,  and  Duane  Smith  at  Lawrence  Livennore  National  Laboratory  for  providing  field  and laboratory  support  to  this  point.  This  work  was  performed  under  the  auspices of the U.S., Department of Energy  by  the  University  of  California,  Lawrence  Livermore  National  Laboratory  under  Contract No. W-7405- Eng-48. 1.9 References Christman,  P.G.,  Gorell, S.B., 1994, Comparison of Laboratory and  Field Observed C02 Tertiary Injectiviw, Journal of Petroleum  Tech., Vol. 226, p. 289. Green, D.W., Willhite, G.P., 1998, Enhanced Oil  Recuvery - Society of Petroleum  Engineers  Textbook  Vol. 6,  Soc. Petroleum  Eng.,  Houston, TX, 545 p. Kirkendall, B.A., Roberts, J.J., 2000, Cross-Borehole  Electromagnetic  Induction at an EOR site: A Joint Field- Laboratory Study, Submitted  to  Journal  of  Geophysical  Research,  also Rep. UCRL-JC-141525,  Lawrence Livermore  National  Laboratory,  Livermore, CA. Kirkendall, B.A., Lewis, J.P., Hunter, S.L., Harben, P.E., 1999, Progress in Crosswell Induction Imagingfor EOR: FieZd System  Design  and  Field  Testing, LLNL Internal  File  Report, UCRL-ID 133468, 17 p. Shyeh-Yung, J-G.J., 1991, Mechanisms of Miscible Oil Recovery: Eflects of Pressure on Miscible  and Near- Miscible  Displacements of Oil by Carbon  Dioxide, paper 2265 1, 199 1 SPE annual  technical  conference  and exhibition,  Dallas, TX, 6 - 9 October. Reservoir Reservoir Reservoir Heater Controller IRI Pressure Control System Figure 2. Schematic of the laboratory device to be used to measure  electrical properties of rocks at high pressure and temperature, System  was  designed to enable the investigation of electrical properties of porous  media under a variety of conditions. There are three  separate pressure control systems, stable temperature control up  to 3OO0C, and computer data acquisition of electrical data and experimental parameters. System  can generate pore pressures up to 10 MPa and is easily adaptable for the use  of COz as a pore fluid. E i c 0 N' E Lost Hills 1803a 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1 Oil injection I Brine injection 1 4 Temperature = 48.9 Pconf = 500 psi Ppore = 100 psi t Figure 3 Electrical resistivity of oil-saturated  diatomite from Lost Hills, CA during  water  injection, Resistivity of some  sample  increases  temporarily  during the brine  injection  process. This helps explain the  relative lack of low resistivity in parts of the well-logs  expected for brine  saturated rocks. A November 1999 2.0 KHz March 2000 2.0 KHz B Q 20 40 60 80 2 3 4 Resistivity a-rn ............ . . .  D 2 4 Resistivity $2-m Figure 4 Electrical  conductivity time-lapse image of a 2.0 kHz tomography at Chevron  Heavy  Oil  Division, Lost Hills, California. The left  image was acquired in November 1999, while the image  on the right was acquired in March 2000. The transmit borehole on the right (indicated by circtes)  corresponds with the long-offset  induction log (A), while the receive  borehole  on the left  corresponds  with induction log (B).  The injection  well and perforation regions, C, is  off-plane  approximately 10 ft. into the paper. The colorbar, D, is in  conductivity (mmeter), Bluish  regions represent the conductive  injection  fluid,  while the reddish regions represent the preexisting oil. C02 would appear as a deeper red  since the conductivity  is  typically  less than oil. L Interest . I  . 2 -. . .IO l2 14 '6 Easting (feet) 16 Figure 5 Gyroscopic data of wells TXC and RXC with the relative location of the injector well (IJO1). The inversion algorithm will not converge with such large well deviations. Newman (2000) has incorporated into a finite difference inversion algorithm factors which accept known well deviations and adjust the resulting electromagnetic fields. 

Electromagnetic Imaging of CO2 Sequestration at an Enhanced Oil Recovery Site

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Electromagnetic Imaging of CO2 Sequestration at an Enhanced Oil Recovery Site

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