William L. Soroka

Coherent and random noise attenuation using the curvelet transform

This paper discusses an effective approach to attenuate random and coherent linear noise in a 3D data set from a carbonate environment. Figure 1 illustrates a seismic inline section from a noisy 3D seismic cube. Clearly, the section in Figure 1 is corrupted by undesirable random noise and coherent noise that are linear and vertically dipping in nature

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.

Comparison of 3D VSP and High Resolution Surface Seismic Images for Improved Reservoir Monitoring and Characterization

Two 126 level 3-component 3D-VSP’s (Vertical Seismic Profiles) were acquired coincident with a high-resolution surface seismic survey. Figure 1 shows the location of the first 3D-VSP on the crest of the field and the second 3D-VSP on the flank of the field. Using the surface seismic sources, 11712 shot points were used per VSP to collect 4.5 million traces per VSP, which produced a 6-9 km² final 3D-VSP image around each of the two wells. Due to the large offsets and high density of traces available it was possible to experiment with acquisition and processing methodologies to produce images that resolve thinner beds, see more structural definition and improve reservoir characterization. Results from the first phase of processing are very encouraging and show the 3D-VSP images to be able to resolve subtle faults that were not seen in older surface seismic data and have higher frequency content than the new 640 fold, high resolution surface seismic data. Source and receiver decimation tests are aiding in efforts to better understand how to acquire high quality 3D-VSP’s in the future with minimal effort and cost. Efforts to expand the size of the 3D-VSP volumes around the wells have been successful. The largest image produced so far has been able to image more than 1.5 km away from the wellbore. The high quality VSP images and the fact that VSPs can be repeated at much lower cost than surface seismic makes this technology very attractive for future time-lapse reservoir monitoring studies.

AVO, Inversion And Rock Physics Modeling Contribute to Makassar Exploration Efforts

SUMMARY Exploration efforts in the Makassar straits by Mobil Oil Indonesia have resulted in the mapping of a number of encouraging pros pects (Malecek, et al., 1993). In an effort to reduce risk and improve the probability for drilling a successful well in this deep wa ter area Mobil Oil Indonesia applied rock physics modeling, poststack seismic inversion and Amplitude Versus Offset (AVO) to better quantify prospects. Rock physics was used to quantify the effects of fluids on seismic responses, inversion was used to help ve rify reservoir and AVO was used to detect the presence of hydrocarbons at the Perintis-1 well location. Based on drilling, the inver sion results correctly predicted the presence of low acoustic impedance layers where hydrocarbon bearing sands were encountered. AVO also correctly showed positive anomalies associated with the low acoustic impedance gas bearing reservoirs. At the first seismi c anomaly with a positive AVO response, the depth predicted by the inversion was 1581 m. Drilling encountered a low acoustic impedance gas bearing sand at 1577 m. When applied properly in an integrated approach the rock physics, inversion and AVO technologies can extract additional useful information from available data that can help answer exploration questions.