Ganglin Chen

Spectral-decomposition response to reservoir fluids from a deepwater West Africa reservoir

Westudythespectral-decompositionresponsetoreservoir fluids from a deepwater WestAfrica reservoir through a systematicmodelingapproach.Ourworkflowstartsfromselecting the seismic data far-angle seismic images that show morepronouncedfluideffectbasedonamplitude-versus-offsetAVOanalysis.Syntheticseismicforwardmodelingperformed at the control well established the quality of the seismicwelltie.Reservoirwedgemodeling,spectraldecomposition of the field and synthetic seismic data, and theoretical analyses were conducted to understand the spectral-decomposition responses. The reservoir fluid type is a main factor controlling the spectral response. For this deepwater reservoir, the amplitude contrast between oil sand and brine sand is higher at low frequencies 15 Hz. In addition, synthetic modeling can help identify the possible frequency band where the amplitude contrast between hydrocarbon sand and brinesandishigher.Whenproperlyincludedinacomprehensive direct-hydrocarbon-indicator DHI‐AVO evaluation, spectral decomposition can enhance the identification of hydrocarbons.

Spectral Decomposition Response to Reservoir Fluids From a Deepwater Reservoir

Summary Spectral decomposition of far-angle stack seismic data from a deepwater reservoir revealed that the oil leg has anomalously high amplitude at low frequencies. A systematic seismic forward modeling study was performed to understand the empirical observations and to identify the primary physical mechanisms. The first part of the study used a wedge model of reservoir sand containing different fluids (gas/oil/water) encased in shale. The second part of the study employed a stochastic simulation approach in which the properties and stacking pattern of the modeled reservoir interval were perturbed to span the range observed in the logs from wells that penetrated this reservoir. Each synthetic seismogram was spectrally decomposed and analyzed.

Stress-induced Velocity Anisotropy of Unconsolidated Sand Under Realistic Reservoir Stress Conditions

Ultrasonic velocity measurements were made on dry and oil saturated samples/cores of unconsolidated sands to investigate the stress-induced velocity anisotropy under realistic reservoir stress conditions. Instrumentation was arranged to simultaneously measure five velocities (axial P, axial S, radial P, radial S polarized radially, and radial S polarized axially) and the axial and radial deformation of the samples in a single run.

Intrinsic P- And S-wave Attenuation of Carbonate Reservoir Rocks From Seismic, Sonic, to Ultrasonic Frequencies

New measurements of Pand S-wave velocity dispersion in carbonate reservoir rocks from seismic (<100Hz) to sonic (~10kHz) and ultrasonic (~1MHz) frequencies were analyzed to derive the frequency-domain intrinsic attenuation spectrum. Three rock samples were analyzed, all with porosity in the same range: one sample had high permeability and two had low permeability. We used the standard linear solid model to describe the twin relationship between velocity dispersion and attenuation. The analysis led to the following observations: (1) P-wave attenuation (1/Qp) and S-wave attenuation (1/Qs) are similar in each of the frequency bands(seismic, sonic, ultrasonic): 1/Qp ~ 1/Qs; (2) The attenuation spectrum in each frequency band has an associated characteristic relaxation distance; (3) For a given carbonate reservoir rock, attenuation in the ultrasonic frequency band can be “anomalously” high (Q~1) but still be “normal” (Q~10-100) in the seismic frequency band.

Reducing Reservoir Characterization Uncertainties and Improving Field Recovery through Four-Dimensional Seismic Technology: An Integrated Four-Dimensional Seismic Interpretation Workflow

More than one-half of the worlds remaining hydrocarbon reserves are in carbonate rocks. Reservoir complexity and heterogeneity in carbonate reservoirs are commonly the main sources of uncertainty in reservoir models and thereby affect field recovery strategies. Four-dimensional seismic technology, which acquires three-dimensional seismic data over a producing field at different times, can provide valuable information on the reservoir changes induced by hydrocarbon production. This information can then be used to better understand the reservoirs complexity, heterogeneity, dynamic flow parameters, and production performance. The application of four-dimensional seismic technology in carbonates is still in an early stage because of many challenges such as detectability and repeatability of four-dimensional seismic data. This chapter provides an overview of the workflow, describes more details through an application to a giant carbonate oil field located onshore Abu Dhabi, and emphasizes reduction of reservoir uncertainties. The workflow consists of the following six steps: (1) rock physics analysis on the effects of fluid and pressure changes on the elastic properties of the reservoir rocks; (2) four-dimensional forward seismic modeling; (3) seismic acquisition geometry analysis, seismic data processing assessment, and postproduction processing data enhancement; (4) qualitative and quantitative four-dimensional seismic data analysis; (5) four-dimensional seismic updating of geologic models; and (6) reservoir simulation feedback using four-dimensional seismic data.

4D Seismic in Carbonates: From Rock Physics to Field Examples

We have carried out 4D seismic research on two giant carbonate fields in Abu Dhabi, UAE, employing an integrated approach. Our work process started from fundamental rock physics analysis. The Xu-White rock physics model, originally designed for clastic rocks, was extended to carbonates. With this model, we characterized the reservoir interval by different (geophysical) pore types, related them to petrophysical (sedimentalogical) pore types, and performed log conditioning to improve well to seismic ties. Laboratory ultrasonic measurements of core plugs and log analysis were conducted in combination with the rock physics model to examine the fluid and pressure sensitivities.