Crosswell Seismic Research Articles

2D High-Resolution Crosswell Seismic Traveltime Tomography

This paper presents a method for combining the hybrid eikonal solver and the prior velocity information to obtain high-resolution crosswell imaging. The hybrid eikonal solver in this technique can ensure rapid and reliable forward modeling of traveltime field in an unsmoothed velocity model. We also utilize the sonic well logging curve to properly develop an initial reference velocity model, and use the sonic well logging data as the prior information for the inversion part, which can restrict the problem of non-uniqueness. The results of the numerical experiment of traveltime in multi-layer media showed that the hybrid eikonal solver was more accurate than the finite difference method. The case study of an oil field in eastern China demonstrated that our method can derive a high-resolution reconstruction of the subsurface structure by inverting the primary traveltime datasets. These results suggest that even though the eikonal equation is a high frequency approximation to the wavefield, the hybrid eikonal solver can provide an accurate traveltime field in the forward modelling step of seismic crosswell tomography, which is critical to ensure high-resolution invert imaging in a highly heterogeneous environment.

Synergizing Crosswell Seismic and Electromagnetic Techniques for Enhancing Reservoir Characterization

SummaryIncreasing complexity of hydrocarbon projects and the request for higher recovery rates have driven the oil-and-gas industry to look for a more-detailed understanding of the subsurface formation to optimize recovery of oil and profitability. Despite the significant successes of geophysical techniques in determining changes within the reservoir, the benefits from individually mapping the information are limited. Although seismic techniques have been the main approach for imaging the subsurface, the weak density contrast between water and oil has made electromagnetic (EM) technology an attractive complement to improve fluid distinction, especially for high-saline water. This crosswell technology assumes greater importance for obtaining higher-resolution images of the interwell regions to more accurately characterize the reservoir and track fluid-front developments. In this study, an ensemble-Kalman-based history-matching framework is proposed for directly incorporating crosswell time-lapse seismic and EM data into the history-matching process. The direct incorporation of the time-lapse seismic and EM data into the history-matching process exploits the complementarity of these data to enhance subsurface characterization, to incorporate interwell information, and to avoid biases that may be incurred from separate inversions of the geophysical data for attributes. An extensive analysis with 2D and realistic 3D reservoirs illustrates the robustness and enhanced forecastability of critical reservoir variables. The 2D reservoir provides a better understanding of the connection between fluid discrimination and enhanced history matches, and the 3D reservoir demonstrates its applicability to a realistic reservoir. History-matching enhancements (in terms of reduction in the history-matching error) when incorporating both seismic and EM data averaged approximately 50% for the 2D case, and approximately 30% for the 3D case, and permeability estimates were approximately 25% better compared with a standard history matching with only production data.

Crosswell seismic applications for improved reservoir understanding

Crosswell seismic (CS) technology provides a high-resolution image of the subsurface between two nearby wells. Crosswell seismic data can reach frequencies greater than 1000 Hz, which makes the technology applicable to many reservoir-development challenges in hydrocarbon exploration and production studies that require high resolution. Applications of crosswell seismic data range from structural and stratigraphic interpretation to reservoir monitoring and enhanced oil recovery (EOR). When integrated with rock physics, crosswell seismic data can be used in reservoir-characterization studies, which potentially could be used for enhancing the resolution of rock properties derived from 3D surface-seismic data to that of crosswell resolution. In addition, velocity models obtained from crosswell seismic data can be used to better predict event locations in microseismic data processing.

Covariance-Based Wavefield Separation and its Application in Crosswell Seismic Data

This paper studied separation algorithms for Seismic signals with time dependence. A covariance-based procedure was adopted to compute the polarization angle in crosswell seismic data, accomplishing the separation of reflecting P wave and conversion SV wave. Numerical experiments show that the width of sliding windows should be 1.5 apparent period of seismogram. The results of experiments illustrate the procedure is effective.

Covariance-Based Wavefield Separation and its Application in Crosswell Seismic Data

This paper studied separation algorithms for Seismic signals with time dependence. A covariance-based procedure was adopted to compute the polarization angle in crosswell seismic data, accomplishing the separation of reflecting P wave and conversion SV wave. Numerical experiments show that the width of sliding windows should be 1.5 apparent period of seismogram. The results of experiments illustrate the procedure is effective.

Application of Crosswell Seismic Technology in the Fine Reservoir Description

According to the instance of crosswell seismic in the district of daqing oil, this paper introduces crosswell seismic data acquisition, the processed results, the application of the parameter inversion and geological interpretation in fine reservoir description. Through these examples, this paper also discusses the crosswell seismic technology development status and further development trend.

SPE Distinguished Lecturer Program 2012-13

Program review Featuring 28 speakers from various disciplines and professions, the 2012–13 Distinguished Lecturer Program emphasizes current industry trends, challenges, and technology through diverse topics. Subject areas and speakers featured in this year’s program are listed here. Advancement in Sand Control Fluid Technology The number of reservoirs requiring sand control is growing at a fast pace. Fluids play an important role in successful design, execution, and performance of sand control completions. This presentation will familiarize the audience with key fluid technologies, examine benefits and limitations, review development processes, demonstrate success with the aid of case histories, and identify technology gaps. Bala Gadiyar is a principal engineer at Schlumberger in Houston. He holds a BS degree from the University of Pune and MS and PhD degrees from the University of Oklahoma, all in petroleum engineering. Improved Recovery and Reduced Costs With Intelligent Interventions—Make Your Wells Intervention Friendly This presentation will offer an operational perspective on the state of light intervention technology available in the industry and how it is changing the way some operators design their wells for intelligent interventions by making them more intervention friendly. It will also discuss the merits of integrating more contingency planning into subsea, intelligent, and unconventional wells based on light well intervention experience within the industry. Brian Schwanitz is a graduate of Michigan Technological University in applied geophysics and has worked in the oilfield service industry for the past 34 years. Crosswell Seismic: Imaging and Monitoring of the Reservoir This talk highlights the resolution benefit of crosswell seismic, including recent technology enhancements in crosswell imaging that make the method suitable in real-world reservoirs and a number of examples from a variety of applications where crosswell seismic adds economic value in reservoir development, both in high-resolution reservoir characterization and reservoir monitoring Bruce Marion is general manager of DeepLook-CS, Schlumberger, in Houston. He has been involved in crosswell seismic technology and operations for more than a decade.

Reservoir characterization and inversion uncertainty via a family of particle swarm optimizers

History matching provides to reservoir engineers an improved spatial distribution of physical properties to be used in forecasting the reservoir response for field management. The ill-posed character of the history-matching problem yields nonuniqueness and numerical instabilities that increase with the reservoir complexity. These features might cause local optimization methods to provide unpredictable results not being able to discriminate among the multiple models that fit the observed data (production history). Also, the high dimensionality of the inverse problem impedes estimation of uncertainties using classical Markov-chain Monte Carlo methods. We attenuated the ill-conditioned character of this history-matching inverse problem by reducing the model complexity using a spatial principal component basis and by combining as observables flow production measurements and time-lapse seismic crosswell tomographic images. Additionally the inverse problem was solved in a stochastic framework. For this purpose, we used a family of particle swarm optimization (PSO) optimizers that have been deduced from a physical analogy of the swarm system. For a synthetic sand-and-shale reservoir, we analyzed the performance of the different PSO optimizers, both in terms of exploration and convergence rate for two different reservoir models with different complexity and under the presence of different levels of white Gaussian noise added to the synthetic observed data. We demonstrated that PSO optimizers have a very good convergence rate for this example, and provide in addition, approximate measures of uncertainty around the optimum facies model. The PSO algorithms are robust in presence of noise, which is always the case for real data.

Case story: time-lapse seismic crosswell monitoring of CO2injected in an onshore sandstone aquifer

SUMMARY We present a case study of time-lapse seismic monitoring of carbon dioxide (CO2) injection by traveltime delay tomography. Unlike standard tomography based on the ray theory, this tomographic method applies the 3-D finite-frequency wavefield theory which in seismology is known as the banana‐doughnut theory. To monitor 4-D changes in the subsurface during CO2 injection, crosswell seismic data were measured before the injection was initiated and after injection of 3200, 6200 and 10 400 tons CO2 into a porous reservoir sandstone at 1100 m depth. The estimated tomographic velocity images compiled with the finite-frequency wave theory show a clear time-lapse velocity anomaly on the order of −18 per cent below the CO2 injection well head which is in agreement with 4-D sonic logging.

Understanding Reservoir Architectures and Steam-Chamber Growth at Christina Lake, Alberta, by Using 4D Seismic and Crosswell Seismic Imaging

Summary EnCana Corporation's Christina Lake Thermal Pilot Project located 170 km south of Fort McMurray, Alberta, Canada, uses steam-assisted gravity drainage (SAGD) technology to recover bitumen from the Lower Cretaceous McMurray formation. This paper presents an analysis of time-lapse and crosswell seismic data, as part of an overall study integrating different disciplines and technologies, to understand the effects of geology on SAGD-process performance in the pilot area. A 3D baseline survey was conducted at the start of the pilot in 2001, and two follow up surveys were conducted in 2004 and 2005. In addition, six crosswell seismic profiles were acquired by placing both sources and receivers in the vertical wellbores. The goal of the seismic surveys was to better understand steam-chamber growth and reservoir architecture by detecting lithology changes, including the occurrence and distribution of mudstone stringers. Data from the surveys, especially from the crosswell profiles, indicated significant reservoir heterogeneity, and helped to characterize reservoir architecture in the pilot area more accurately. Analysis of seismic data (both 4D and crosswell) showed steam-chamber growth and oil recovery to be influenced strongly by reservoir geology. Steam-chamber growth is especially affected by the presence of low-permeability facies in the vicinity of the SAGD well pairs. Our analysis indicates that these reservoir heterogeneities have contributed to the creation of areas within the reservoir that have been unaffected by steaming operations to date. These findings are in agreement with flow-simulation results and collectively contribute significantly to the planning of future developments.

Validation of first-order diffraction theory for the traveltimes and amplitudes of propagating waves

Ultrasonic measurements of acoustic wavefields scattered by single spheres placed in a homogenous background medium (water) are presented. The dimensions of the spheres are comparable to the wavelength and the wavelength and represent both positive (rubber) and negative (teflon) velocity anomalies with respect to the background medium. The sensitivity of the recorded wavefield to scattering in terms of traveltime delay and amplitude variation is investigated. The results validate a linear (first-order) diffraction theory for wavefields propagating in heterogeneous media with anomaly contrasts on the order of [Formula: see text]. The diffraction theory is compared further with the exact results known from literature for scattering from an elastic sphere, formulated in terms of Legendre polynomials. To investigate the 2D case, the first-order scattering theory is tested against 2D elastic finite-difference calculations. As the presented theory involves a volume integral, it is applicable to any geometric shape, and the scattering object does not need to be spherical or any other specific symmetrical shape. Furthermore, it can be implemented easily in seismic data inversion schemes, which is illustrated with examples from seismic crosswell tomography and a reflection experiment.

Crosswell seismic imaging in a contaminated basalt aquifer

Multiple seismic crosswell surveys have been acquired and analyzed in a fractured basalt aquifer at Idaho National Engineering and Environmental Laboratory. Most of these surveys used a high‐frequency (1000–10,000 Hz) piezoelectric seismic source to obtain P‐wave velocity tomograms. The P‐wave velocities range from less than 3200 m/s to more than 5000 m/s. Additionally, a new type of borehole seismic source was deployed as part of the subsurface characterization program at this contaminated groundwater site. This source, known as an orbital vibrator, allows simultaneous acquisition of P‐ and S‐waves at frequencies of 100 to 400 Hz, and acquisition over larger distances. The velocity tomograms show a relationship to contaminant transport in the groundwater; zones of high contaminant concentration are coincident with zones of low velocity and high attenuation and are interpreted to be fracture zones at the boundaries between basalt flows. The orbital vibrator data show high Vp/Vs values, from 1.8 to 2.8. In spite of the lower resolution of orbital vibrator data, these data were sufficient for constraining hydrologic models at this site while achieving imaging over large interwell distances. The combination of piezoelectric data for closer well spacing and orbital vibrator data for larger well spacings has provided optimal imaging capability and has been instrumental in our understanding of the site aquifer's hydrologic properties and its scale of heterogeneity.

Mathematics of Multidimensional Seismic Imaging, Migration, and Inversion. Interdisciplinary Applied Mathematics, Vol 13

<i>Mathematics of Multidimensional Seismic Imaging, Migration, and Inversion. Interdisciplinary Applied Mathematics, Vol 13</i>

Using seismic crosswell surveys to determine the aperture of partially water‐saturated fractures

An air injection experiment in a shallow fractured limestone at Conoco’s borehole test facility near Newkirk, Oklahoma, has shown large effects on the amplitude but small effects on the traveltime of the transmitted seismic waves. We have analyzed data from a seismic monitor survey in the kilohertz range performed during the experiment and have modeled the fracture zone as a single fracture. The large amplitude decrease during the experiment is mainly attributable to the impedance contrast between the small velocities of gas‐water mixtures inside the fracture and the formation. The intrinsic attenuation of the fracture fluid seems to be a second‐order effect for small apertures. During the experiment the seismic wavelengths inside the fracture become comparable to the aperture dimension, which allows an estimation of fracture apertures. We also have analyzed a crosswell survey acquired shortly after the experiment and computed aperture and gas concentration profiles. Our aperture estimates range from &lt;1 mm to a few millimeters, which is comparable to previous tracer tests. The results of this study are generally consistent with prior hydrologic work and single‐well surveys. This study demonstrates that crosswell surveys could be an effective tool for obtaining in situ estimates of fracture aperture and gas concentration.

Interwell Property Mapping With Crosswell Seismic Attributes

This article is a synopsis of paper SPE 38747, "Interwell Property Mapping Using Crosswell Seismic Attributes," by Adwait Chawathe, SPE, Ahmed Ouenes, SPE, W.W. Weiss, SPE, New Mexico Petroleum Recovery Research Center originally presented at the 1997 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 5-8 October.

Abstract: Crosswell Seismic Imaging at the McElroy CO[2] Pilot&amp;nbsp;

Abstract: Crosswell Seismic Imaging at the McElroy CO[2] Pilot&amp;nbsp;

Crosswell Seismic Data from a Carbonate Reservoir - Geologic Investigation and Implications for Reservoir Characterization: ABSTRACTS

Crosswell Seismic Data from a Carbonate Reservoir - Geologic Investigation and Implications for Reservoir Characterization: ABSTRACTS

Tomographic reconstruction of near‐borehole slowness using refracted borehole sonic arrivals

Two‐dimensional (2-D) reconstructions of the near‐borehole slowness field are computed using arrival times of refracted borehole sonic arrivals. First‐arrival traveltimes, derived from both computer simulations and field data from full‐waveform sonic tools, were inverted for the near‐borehole formation slowness both axially along the borehole and radially away from the borehole. The inversion is nonlinear; the solution is obtained by means of a series of linear inversions followed by provisional ray tracings. Each iteration involves the application of a tomographic reconstruction algorithm similar to those used in seismic crosswell tomography or medical imaging applications. The technique was demonstrated using ray‐theoretic examples to simulate radial variations in slowness. In addition, full‐waveforms were generated using two‐and‐a‐half‐dimensional (2.5-D) FDM computer models. The finite‐difference method (FDM) computer models were used to test the validity of the ray‐theoretic approximation used in the inversion scheme and to simulate the full‐waveform sonic tool response for both radial and axial changes in formation properties. Field data examples highlighted radial changes in formation slowness caused by two separate mechanisms: water take up by swelling shales and the mechanical breakdown of the near‐borehole rock resulting from stress relief caused by the drilling process. Finally, refracted sonic arrivals from near‐borehole bed boundaries were identified in a horizontal well setting. Using refractions arriving beyond the headwave, a 2-D map of formation slowness was computed in the reservoir away from the borehole. Interpretation of the slowness map resulted in an estimation of the stand‐off of the horizontal borehole from the reservoir boundary.