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Title: Exploiting P-S converted waves. Part 2: Application to a fractured reservoir

Abstract

A P-S data set, with nearby well data for analysis constraint, was collected in southwest Venezuela to map the strike, density, and extent of fractures in the hydrocarbon bearing formation of a reservoir. Three 10 km multicomponent lines were centered over the reservoir along three different azimuths. The survey design was geared to maximize the data quality with respect to resolution, signal-to-noise ratio, sufficient spatial and temporal sampling, correct near and far offsets, maximum dip, and elimination of any variation in amplitude or traveltime that can be confused with lithological effects. Well information indicates that the hydrocarbon bearing formation is a fractured limestone with a depth of approximately 3,000 m, and gently dipping in a NE-SW direction. Based on previous seismic P-wave data, subtle lithological structures and small normal faults dominate the reflection horizons of the target zone. These structures appear to dominate the production history of the existing wells in the field, which implies the necessity of high resolution data for better definition of the seismic events. Results from the collected data suggest presence of azimuthal anisotropy that effects P-S converted-wave amplitude and traveltime. Observations appear to be consistent with the geological setup in the area of study. However,more » accurate quantification of anisotropic parameters must be done after appropriate processing of the data and careful confirmation of results with borehole measurements.« less

Authors:
; ;  [1]; ;  [2]
  1. Intevep S.A., Caracas (Venezuela)
  2. Corpoven S.A., Caracas (Venezuela)
Publication Date:
OSTI Identifier:
80199
Report Number(s):
CONF-941015-
Journal ID: ISSN 1052-3812; TRN: IM9532%%326
Resource Type:
Conference
Resource Relation:
Conference: 64. annual meeting of the Society of Exploration Geophysicists and international exposition, Los Angeles, CA (United States), 23-27 Oct 1994; Other Information: PBD: 1994; Related Information: Is Part Of SEG international exposition and sixty-fourth annual meeting -- 1994 Technical program: Expanded abstracts with authors` biographies; PB: 1736 p.
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; 03 NATURAL GAS; 58 GEOSCIENCES; SEISMIC SURVEYS; DATA PROCESSING; PETROLEUM DEPOSITS; SEISMIC WAVES; ANISOTROPY; VENEZUELA; RESPONSE FUNCTIONS; MATHEMATICAL MODELS

Citation Formats

Ata, E., Michelena, R.J., Gonzales, M., Cerquone, H., and Carry, M. Exploiting P-S converted waves. Part 2: Application to a fractured reservoir. United States: N. p., 1994. Web.
Ata, E., Michelena, R.J., Gonzales, M., Cerquone, H., & Carry, M. Exploiting P-S converted waves. Part 2: Application to a fractured reservoir. United States.
Ata, E., Michelena, R.J., Gonzales, M., Cerquone, H., and Carry, M. 1994. "Exploiting P-S converted waves. Part 2: Application to a fractured reservoir". United States. doi:.
@article{osti_80199,
title = {Exploiting P-S converted waves. Part 2: Application to a fractured reservoir},
author = {Ata, E. and Michelena, R.J. and Gonzales, M. and Cerquone, H. and Carry, M.},
abstractNote = {A P-S data set, with nearby well data for analysis constraint, was collected in southwest Venezuela to map the strike, density, and extent of fractures in the hydrocarbon bearing formation of a reservoir. Three 10 km multicomponent lines were centered over the reservoir along three different azimuths. The survey design was geared to maximize the data quality with respect to resolution, signal-to-noise ratio, sufficient spatial and temporal sampling, correct near and far offsets, maximum dip, and elimination of any variation in amplitude or traveltime that can be confused with lithological effects. Well information indicates that the hydrocarbon bearing formation is a fractured limestone with a depth of approximately 3,000 m, and gently dipping in a NE-SW direction. Based on previous seismic P-wave data, subtle lithological structures and small normal faults dominate the reflection horizons of the target zone. These structures appear to dominate the production history of the existing wells in the field, which implies the necessity of high resolution data for better definition of the seismic events. Results from the collected data suggest presence of azimuthal anisotropy that effects P-S converted-wave amplitude and traveltime. Observations appear to be consistent with the geological setup in the area of study. However, accurate quantification of anisotropic parameters must be done after appropriate processing of the data and careful confirmation of results with borehole measurements.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1994,
month =
}

Conference:
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  • The authors performed extensive modeling studies to evaluate P-S converted waves effectiveness and limitations in the estimation of both cracks orientation and density. The target area is a fractured, carbonate reservoir located in south-west Venezuela. The reservoir depth is on the order of 3000 m, which implies that high quality P-S data are needed to obtain detectable information about the anisotropy at this depth. They focused their analysis on P-S converted waves because only explosives charges were available as energy sources. The modeling was performed prior to and after the data acquisition to help both design of the experiment andmore » interpretation of the data. Synthetic seismograms were generated using 2D, elastic finite difference, along with a 3D-3C, paraxial ray tracing codes. They conducted also a noise-spread test to complement this study and determine the acquisition parameters. A 3D velocity model of the subsurface was built based on previous P-wave seismic sections, well logs (dual-sonic, density, check-shots and FMS), geological maps, and production information. This model was perturbed in a layer stripping fashion until an acceptable match was obtained around the depth of interest between synthetic and multicomponent field data. The anisotropy produced measurable differences in traveltimes and amplitudes between in-line and cross-line components. These differences (which are comparable to those observed on the field data) suggest that it is feasible to map fractures at depths around the reservoir area by using P-S converted waves.« less
  • We discuss results of detailed numerical and analytical studies on the propagation of ion-Bernstein waves (IBW) in a toroidal plasma. Such waves can be excited by mode conversion of an externally launched fast Alfven wave near the ion-ion hybrid resonance (or near the second harmonic resonance for a single ion species plasma) in a tokamak. We find that there is a significant upshift in the poloidal mode numbers of the IBW over short radial distances of propagation so that the IBW can Landau damp onto the electrons. The numerically obtained results are corroborated by a simple analytical model. 4 refs.,more » 4 figs.« less
  • Oil is produced primarily from open fracture porosity in Upper Cretaceous chalk in the Sidi El Kilani oil field. Strontium Stratigraphy analyses of primary, unaltered matrix chalk has confirmed a Campanian to Maastrichtian age and has allowed dating of the reservoir with a resolution of [+-]1 Ma. This has facilitated reservoir correlation and has indicated where section is missing in certain wells due to faulting. [sup 87]Sr/[sup 86]Sr, [delta][sup 18]O and [delta][sup 13]C analyses suggest an early generation of fracture fill calcite cement may have formed by redistribution of CaCO[sub 3] from underlying carbonate sequences at temperatures in the regionmore » 35-55[degrees]C. Calcite cemented fractures tend to be healed and are not productive. Strontium Isotope Residual Salt Analyses (SrRSA) conducted on core, provide information on the formation water chemistry and reservoir connectivity at the time of oil filling. These data suggest that the NW-SE trending fault system that bisects the field is sealed across much of the fault plane. The main oil pool lies SW of the fault. A later generation of dolomite and barite cements, associated with productive open fractures, have Sr-O-C composition consistent with precipitation from fluids circulating at the time of hydrocarbon charge at temperatures close to current reservoir conditions of 70-75[degrees]C. Predicting the distribution of dolomite cemented open fractures has thus helped guide the development strategy of the field.« less
  • This paper introduces the concept of ''relative diffusion flux'', a new and practical approach to characterize the dissolution and diffusion regulated transfer of gas from the gas filled fracture space to the matrix oil in a dual porosity/permeability system. The proposed concept is analogous to the relative permeability concept in that the ''effective diffusion (or transfer) flux'' is determined as the product of the ''absolute (maximum) diffusion flux'' capacity of the matrix and the current level of ''relative diffusion flux''. It is shown that the latter can be expressed as a function of the current dissolved gas concentration in themore » matrix oil. This functional relationship between the ''relative diffusion flux'' and the dissolved gas concentration in the matrix oil is similar, in concept, to that between the relative permeability to a phase and its saturation level. It is also shown that, using the proposed method, representation of the gas transfer mechanism is reduced to a simple exchange-type relationship between the fractures and the matrix. This is achieved without having to determine an appropriate diffusion coefficient and the task of handling gas transfer by diffusion is significantly facilitated for fractured reservoir simulators. In the paper the concept of ''relative diffusion flux'' is developed, a method for obtaining the required data from a suitable laboratory experiment is provided, and the basic equations for the application of the new concept to fractured reservoir simulation are derived.« less
  • Oil is produced primarily from open fracture porosity in Upper Cretaceous chalk in the Sidi El Kilani oil field. Strontium Stratigraphy analyses of primary, unaltered matrix chalk has confirmed a Campanian to Maastrichtian age and has allowed dating of the reservoir with a resolution of {+-}1 Ma. This has facilitated reservoir correlation and has indicated where section is missing in certain wells due to faulting. {sup 87}Sr/{sup 86}Sr, {delta}{sup 18}O and {delta}{sup 13}C analyses suggest an early generation of fracture fill calcite cement may have formed by redistribution of CaCO{sub 3} from underlying carbonate sequences at temperatures in the regionmore » 35-55{degrees}C. Calcite cemented fractures tend to be healed and are not productive. Strontium Isotope Residual Salt Analyses (SrRSA) conducted on core, provide information on the formation water chemistry and reservoir connectivity at the time of oil filling. These data suggest that the NW-SE trending fault system that bisects the field is sealed across much of the fault plane. The main oil pool lies SW of the fault. A later generation of dolomite and barite cements, associated with productive open fractures, have Sr-O-C composition consistent with precipitation from fluids circulating at the time of hydrocarbon charge at temperatures close to current reservoir conditions of 70-75{degrees}C. Predicting the distribution of dolomite cemented open fractures has thus helped guide the development strategy of the field.« less