Srinivasa Rao Narhari

PP Azimuthal-amplitudes And -acoustic Impedance For Fractured Carbonate Reservoir Characterization

Four azimuth-sectored 3D P-P volumes were pre-stack time migrated (PSTM) using the same velocity field. These high-fold full-azimuth full-offset data (4,000-5,000 traces were summed in each bin in each azimuth sector) of high S/N enable azimuthal analysis of amplitudes, and acoustic impedance, at the top of the reservoir unit of interest (14,000 ft depth). Each azimuthal cube was inverted for acoustic impedance after prestack time migration. These high-fold azimuth-sectored PSTM 3D data enable us to determine the azimuthal variation of amplitudes, and acoustic impedance, assuming orthorhombic symmetry (flat layers and one set of vertical aligned frctures), and so map relative fracture density and fracture azimuth of the open fractures that flow hydrocarbons in the reservoir unit. The N-S natural fracture strike seen at Well A in the reservoir unit are parallel to the local max hor stress, as interpreted through borehole breakout and the induced fractures. The N-S trending fractures at Well B cause the fracture-parallel amplitude to be the azimuthal minimum, for the top of this low-impedance reservoir. The acoustic impedance inversions showed max acoustic impedance N-S, parallel the fractures and max hor stress, corroborating the interpretation of the azimuthal amplitudes, and tieing the well data. The spatial heterogeneity of the fractures in the upper part of the reservoir unit is mapped using the azimuthal variation of PP amplitudes, and acoustic impedance, after fitting to the cosine 2theta curve.

Seismic Attributes In the Search For Fracture Plays

Summary: Fracture detection and characterization is gaining importance in the oil industry with the increased focus on hitherto less explored unconventional reservoirs. Seismic attributes play an invaluable role in identifying fracture corridors and help in locating ‘sweet spots’ for placing exploratory and development wells. This paper presents a suite of seismic attributes that were used in the identification of such ‘sweet spots’ in the Middle Jurassic Najmah-Sargelu fracture play of North Kuwait. Seismic attributes analyzed in this study were categorized under three broad groups: a. Trace - Amplitude, Frequency and Phase, b. Geometry - Dip, Azimuth and DipAzimuth c. Image enhancement - Coherence, E dge and Spectral Decomposition. Attribute analysis is augmented with other characterization techniques such as curvature analysis and Geomechanical modeling, which has helped in high grading areas of potential fracture corridors and contributed to the selection process of exploratory locations for this play. Exploration wells drilled based on this integrated analyses have yielded rich dividends by identifying zones of high fracture density.

Sweetspotting of the First Appraisal Campaign of Unconventional Resource Play in Kuwait

Organic rich Kerogen layer of Lower Kimmeridgian to Upper Oxfordian age, deposited throughout Kuwait, is a TOC rich layer with varying TOC content between 2 to 20 wt% (in the vertical section) and having an average TOC of about 8 wt%. The depth of occurrence of this layer favorably places this zone to be having potential in rich gas condensate resource in the northern part of Kuwait. This layer occurs at a depth of 14000-16000 ft with a reservoir temperature of 270⁰-275⁰F, pressure of 11000 psi and average thickness of over 50ft. This is one of the main source rocks for majority of the oil and gas fields of Kuwait. This Kerogen section is penetrated through a number of vertical wells, as part of development of deeper reservoirs in this area, which offers an excellent opportunity to evaluate this section through core and open-hole log data. Because of the strong acoustic contrast with the overlying and underlying layers, this reservoir section is a very strong mappable seismic reflector. As part of appraising the potential of this layer, as a resource play, a comprehensive success criteria has been worked out for location selection. An integration of all available geo-scientific data such as geochemical, 3D seismic attributes, petrophysical analysis, borehole image interpretations, geo-mechanical, core and mud logs has been carried out. The above data integration/analysis was combined with the success criteria, leading to selection of sweet-spots for planning the first dedicated horizontal well targeted on this layer. This paper presents the success criteria worked out and the integration of data for high grading the locale – sweet-spots, for the first set of horizontal wells for appraising this deep HP-HT unconventional play of Kuwait.