SEQUENCE STRATIGRAPHY OF LOWER CRETACEOUS CARBONATES IN UMM GUDAIR OIL FIELD, WEST KUWAIT

The interpretation of the sequence stratigraphy cycles and the surfaces in the Middle Minagish formation was the main target in this research. This target was achieved by defining the maximum flooding surfaces and sequence boundaries in a carbonate ramp environment in Umm Gudair field. Four sequence boundaries and four maximum flooding surfaces were determined in the formation by using two wells WUG-A and EUG-A wells. The sequence stratigraphy interpretation was achieved by integrating lithological, biostratigraphic and seismic data. Core data and thin sections were combined with well logs and microfossils to establish the sequence stratigraphic model for three major wells in east and west anticlines and in the saddle area (WUG-A, EUG-A and SA-UG-A well). For the lithological aspect, ten lithofacies were determined by using EUG-A and WUG-A cored and thin sections data. The reservoir consists of peloidal ooidal packstones and grainstones lithofacies. Eight microfossils were identified to determine the age dating, depositional environment and the water depth of the carbonate ramp environment of the study area. Calpionellids, benthic foraminifera and calcareous algae are major microfossils determined in the study area. The microfossils data provides the identification to determine the fourth order cycles, the water depth and the age dating in the middle Minagish formation. The fourth order cycle includes sixteen cycles and the age of these cycles were determined to be around 0.4 My in the early Cretaceous. Calpionellids are the main microfossils utilized for the age dating in middle Minagish formation. The seismic data analysis includes generating synthetic seismograms and calculating different seismic attributes. Ricker wavelets with dominant frequencies of 25 to 40 Hz in addition to the statistical extracted wavelet were generated for the well-to-seismic reflection data tying. Ricker wavelet of 30 to 35 Hz produced the best fit of the synthetic seismogram with the original seismic data. Where the generated synthetic trace using Ricker wavelet of 30 to 35 Hz provide good match with the original seismic traces of peaks and troughs. Another important part in the seismic data is the seismic attributes. The first derivative, the second derivative, the relative acoustic impedance and the envelope are considered seismic attributes and were calculated from the original seismic record. These attributes were used to understand the relationship between different applications of the seismic attributes and determining the maximum flooding surfaces and the sequence boundaries of the study area. The main purpose of using seismic attributes is to observe high contrast seismic reflections. The high contrast between layers refers to the variations of density and sonic logs in addition to the variations in the reservoir properties. The variations in the reservoir physical properties produce the high contrast boundaries that result in the larger amplitude reflections. The maximum flooding surfaces and sequence boundaries are considered the major stratigraphic surfaces separating between these layers. The colored envelope, the relative acoustic impedance and the second derivative of the relative acoustic impedance have the most detected surfaces of the seismic attribute. The MFS4 and the MFS3 are the only surfaces were having the best seismic continuity from east to west anticlines