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Evaluating the Shaly Sand Oil Reserviors of El Tordillo Field, Argentina, Using Magnetic Resonance Logs*
By
Maged Fam1, Luis P. Stinco2, and Julio. A. Vieiro2
Search and Discovery Article #40157 (2005)
Posted June 27, 2005
*Adapted from extended abstract, prepared by the authors for presentation at AAPG International Conference & Exhibition, Cancun, Mexico, October 24-27, 2004.
1Halliburton Energy Services, Houston, Texas ([email protected])
2Tecpetrol S.A., Chubut, Argentina ([email protected])
Introduction
El Tordillo field was discovered in 1932 and was operated by YPF (the national oil company) from 1932 until 1991. In 1991, the Consortium El Tordillo, in which Tecpetrol S.A. is the operator, assumed operations.
The field is situated on the north flank of the San Jorge Basin in Chubut Province, Argentina. It is approximately 50 kilometers from the town of Comodoro Rivadavia and 1500 kilometers south of Buenos Aires (Figure 1). More than 1200 wells have been drilled in the field, and production is spread over approximately 57 square kilometers.
Three Cretaceous units produce the numerous fluvial sand bodies that structurally and stratigraphically trap hydrocarbons in the field. Relevant geological, geophysical, and engineering observations from studies performed within the field can be found in Muruaga et al. (2001) and Taboada et al. (2001). See also Fitzgerald et al. (1990).
The main objectives for running MRIL logs in El Tordillo field were:
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Determination of porosity
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Evaluation of permeability to help identify reservoir quality zones
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Determination of variations in oil viscosity, if any
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Petrophysical Properties of the ReservoirsBoth Comodoro Rivadavia and Mina El Carmen formations consist of feldspathic shaly sandstones with volcanic tuff and conglomerates. A summary of the reservoir characteristics is presented in Figure 2. Additional information can be found in Stinco et al. (2001).
MRIL TechnologyMagnetic Resonance Imaging Logging (MRILPrime ®) service measures several key factors that influence the ability of a well to produce commercial quantities of oil or gas.
One of the fundamental measurements of the
MRIL-Prime tool is total fluid-filled porosity. MRIL in general is a
fluids-only measurement as the rock matrix is invisible to the tool;
therefore, it is unaffected by matrix effects that can influence
conventional logs. In fact, the total porosity measurement is the sum of
clay- In addition, the MRIL tool derives a permeability measurement and is able independently to determine fluid type, pick fluid contacts, and detect changes in oil viscosity.
MRIL Porosity and Permeability Coates et al. (1999) provide a thorough explanation of the theory and the procedures for determining MRI-based porosity and permeability. It should be noted that, in general, the MRIL permeability should be used initially to compare good-quality from poor-quality reservoirs in a relative fashion. When calibrated to MRI core analysis, MRIL permeability can be used in its absolute form. See Marschall et al. (1999) for discussion.
MRIL Analysis and Interpretation Models In order to achieve the objectives of the study, different models of analysis and interpretation were used. They are:
Refer to Coates, et al., (1999) for explanations of these individual methods.
Evaluating The Shaly Sands Oil Reservoirs Of El Tordillo FieldThe main problem to solve when dealing with these reservoirs is that the responses of conventional logs do not always indicate fluid types. These shortcomings have been documented by post-logging well testing.
Pre-Job PlanningA job plan for acquiring MRIL data in El Tordillo field wells was made in this study, based on specific parameters from the well design and anticipated formation and hydrocarbon characteristics (Fam, 2003). The plan was designed to acquire MRIL data that would provide the best opportunity of meeting objectives.
MRIL-Prime Interpretation Compared to Testing ResultsFigures 3 and 4 illustrate the powerful capabilities of MRI logging. A good match is seen between the MRIL prediction of light oil (or high GOR oil) and a test that produced light oil or with some gas (Figure 3).
Figure 4 shows
a different situation. Here the MRIL prognosis called for oil with some
As a consequence of these good matches between forecasts and the test results, a high level of confidence was achieved for forecasting fluid types using MRIL logging in different intervals for the Comodoro Rivadavia and Mina El Carmen formations.
ReferencesCoates, G., Xiao, L., and Prammer, M., 1999, NMR logging principles and applications: Halliburton Energy Services. 234 p. Fam, M., 2003, MRIL-Prime analysis and evaluation report: Internal Report, Halliburton Energy Services.27 p. Fitzgerald, M., Mitchum, R., Uliana, M., and Biddle, K., 1990, Evolution of the San Jorge Basin, Argentina: AAPG Bulletin, v. 74, p. 879-920 p. Marschall, D., Gardner, J., Mardon, D., and Coates, O., 1995, Methods for correlating NMR relaxometry and mercury injection data: 1995 SCA Conference, paper number 9511. Muruaga, E., Antunez, E., Nogaret, C., Stancel, S., 2001, Integrated reservoir study in El Tordillo Field: 2001 SPE Latin American and Caribbean Petroleum Engineering Conference, Buenos Aires, March 25-28. Paper SPE 69688. Stinco, L., Elphick, R., and Moore, R., 2001, Electrofacies and production prediction index determination in El Tordillo Field, San Jorge Basin, Argentina: Paper UU. SPWLA, 42nd Annual Symposium. Houston, Texas, 14 p. Taboada, R., Condat, P., Corsini, V., Mir, E., Conti, J., Fortunato, G., and Villivar, O., 2001, El Tordillo reservoir static characterization study: El Tordillo Field, Argentina: 2001 SPE Latin American and Caribbean Petroleum Engineering Conference, Buenos Aires, March 25-28. Paper SPE 69660.
AppendixTrack # 1 displays the GR curve in green, SP in red, and Caliper shaded yellow from bit size. Also presented are 10 raw MRIL porosity curves on scale 30 – 0 %. The shading between these porosity curves present the corresponding T2 times associated with that porosity curve. The T2 relaxation time ranges from 4 - 1024 msec.;variation of porosity value at different T2 relaxation time depends on fluid type and pore size. Track # 2 is the depth track displaying the depth in meters and a bad hole flag in black shading. Track # 3 shows the deep resistivity curve in dashed black, medium resistivity curve in dotted blue, and the shallow curve in solid magenta. Permeability curve is presented in solid red. All curves are presented on logarithmic scale from 0.2 – 2000. Track # 4 displays the raw T2 spectra from the data acquired with long wait “Tw” and short inter-echo spacing ‘Te”. The color indicates porosity such that the brighter the color the higher the porosity. The lateral logarithmic scale presents the T2 relaxation time on scale 0.3 – 3000.
Track # 5 displays the
differential T2 spectra (the difference between the T2
spectra of the long Tw and the short Tw). Again the color
indicates porosity such that the brighter the color the higher the
porosity. The lateral logarithmic scale presents the T2
relaxation time on scale 0.3 – 3000. In general the differential T2
spectra signal in this track presents either light hydrocarbon or
Track # 6 displays the
final MRIL porosity, on scale 30 – 0 %, after applying the Hydrogen
Index and the T1 corrections. This final MRIL porosity is
obtained after processing the data using the Time Domain Analysis “TDA”
technique. The dashed light green shading indicates clay
Track # 7 displays MRIAN
analysis, which is based on the “Dual
Track # 8 displays the
Enhanced Diffusion Method “EDM” interpretation directed towards
intermediate oil viscosities ranging from 2 – 50 cP. The dashed light
green shading indicates clay Track # 9 displays the raw T2 spectra from the data acquired with long wait “Tw” and short inter-echo spacing ‘Te”. The yellow color indicates porosity such that the higher the amplitude of the yellow shading the higher the porosity. The lateral logarithmic scale presents the T2 relaxation time on scale 0.3 – 3000.
Track # 10
displays the raw T2 spectra from the data acquired
with long wait “Tw” and long inter-echo spacing ‘Te”. The
blue color indicates porosity such that the higher the amplitude of the
blue shading the higher the porosity. The lateral logarithmic scale
presents the T2 relaxation time on scale 0.3 – 3000. The dark
blue vertical line presents the T2DW (T2 diffusion of
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