Y.U. MIRZOYAN, YU. FEDOROVSKY, V. KUTYCHKIN, I. TANYGIN, A. KUROCHKIN

"Ingeoseis", Russia, "Syntez-Capital", Russia, "Arctic Shelf", Russia, FGUP "Arcticmorneftegazrazvedka", Russia, "Ingeovector", Russia

Vector Vertical Seismic Profiling (WSP) is a key tool for seismic waves propagation studies. The WSP specifics relate to vector acquisition of seismic waves to enable selection and correlation of various types of seismic waves (P, S and P converted to S) in order to attain the most comprehensive characterization of geologic media.

The WSP selection of various types of seismic waves is based upon a calculation of the so called "tracking wave component" for each separate wave with maximum signal-to-noise ratio, while polarization filtration is used to correlate and reliably identify seismic wave types.

The WSP data acquisition requires three- or four-component (3C or 4C) geophones. Our preference is symmetric homogenous 4C (I, II, III, Z) geophones by Galperin's design, which enables continuous identity control over components of the 3C geophone units. The applied 24-digit CPU VSP tools, with a multi-level coding and a delta-sigma signal modulation has provided highly precise acquisition of elastic transients in boreholes, which are noise- and weathering zone-free.

Special WSP data processing software has been developed to obtain reliable data on compression and share wave velocities, stratigraphic correlation, the hydrocarbon-linked elastic and absorption seismic attributes. A combination of the detailed CDP and WSP surveys makes it possible to characterize reservoirs more precisely and optimize an exploration and production well grid. The WSP-based prediction of hydrocarbon and reservoir presence in the vicinity of a well as well as below a borehole bottom serves to improve drilling success and cut a number of dry holes substantially.

The paper deals with a series of WSP studies to predict and characterize hydrocarbon reservoirs at various offshore plays in the Arctic, the Far East, the Black Sea and the Azov Sea as well as onshore blocks within the North Caucasus oil and gas province, including Krasnodar, Stavropol and Rostov regions of the Russian Federation.

For the Arctic shelf, the WSP studies have been accomplished in areas with different seismic and geologic environment such as Shtokmanovskoye and Murmanskoye gas and condensate fields, Varandeiskoye and Medynskoye oil fields and others. Key objectives of the surveys have been velocity and wave field analysis in order to provide a reliable stratigraphic correlation, forecast hydrocarbons and delineate reservoirs. Quality WSP data acquision in the Arctic shelf pioneered at Murmanskoye gas field. This allowed to select and correlate compression and share wave fields, derive their velocity, absorption and polarization attributes, study elasticity and deformation modules and establish the latters' link to lithology and rock properties and map abnormally high pressure zones.

At Varandeiskoye, the WSP technology allowed for a polar coordinate correlation of seismic waves. As a result, we have established a very strong correlation between hydrocarbon saturation and trajectories of earth particles as witnessed by complex polarization of seismic waves. At Shtokmanovskoye, a complex interpretation of logging, CDP and WSP data has provided a reliable mapping of the Jurassic gas reservoir and resulted in preliminary reserves estimate. In addition to a geologic section study at Medynskoye, a zero-offset WSP has revealed hydrocarbon anomalies attributable presumably to the Lower Devonian and Silurian sections.

The detailed VVSP survey has been carried out offshore Okhotsk Sea at the Vertical spacing was 10 meters, sampling - 1 msec, record length - 6 sec. We used our proprietary VVSP tool and acquisition unit called Vector-1.

In addition of a set of velocity, polarization, elasticity and deformation attributes, we built-up migrated depth CDP sections to forecast hydrocarbon presence. This allowed us to identify anomalies of our proprietary "SAEE" attributes that necessitated re-processing of the existing CDP data set of earlier vintage. Our conclusion has been, Astrakhanovskoye is not dry. Despite the deposit is likely damaged by faults within a cross of the structure, its northwest part appears hydrocarbon-bearing.

WSP data has also been acquired at the north-west of the Black Sea shelf for a series of blocks such as Flangovoye, Karkinitskoye, Shtilevove and Shmidt. Both conventional and walkaway VVSP wave fields are materially influenced by strong share waves. These enabled us to study the geologic section anisotropy and fracturing zones and map reef traps, which are crucial for identification of the Cretaceous gas reservoirs, regional exploration play.

Separately, the WSP technology shows high efficiency of identifying and mapping missed or poorly drained oil zones within mature reservoirs at the south flank of the West-Kuban trough, particularly at Dysh, South Klutchevoye and East Usun fields. Consequent to a complex analysis of different seismic waves (P, PS, PP, etc.) we have received a set of attributes such as g and s and proprietary "SAEE" attribute to map non-drained oil zones. Consequent to our projections, drilling has attained a 100% success rate, resulting in producing wells with flow rates from mid-Maikop section ranging from 75 bpd and above.

It becomes obvious the VVSP technology at maturing oil and gas fields with well-established infrastructure is extremely economically efficient. Our technology could prove successful for different geologic condition, both onshore and offshore as it is based upon advanced acquisition, processing and interpretation of vector seismic data.

ARCTIC SHELF OIL AND GAS CONFERENCE 2004