Study Of Explotarary Potential Of Block 18,lower Congo Basin

Block18 is located in south Lower Congo Basin, where transitional salt tectonic belt develops and 8 oilfileds has been discovered. The principal source rock in the block is the pre-salt middle rift phase Barremian lacustrine shales and Turonian-Teriary Iabe formation marine shales. The main reservoir is the turbidite sands of the Oligocene and Miocene age respectively. They are sealed by upper Cretaceous and Tertiary marine shales: Landana and Malembo formation. The block lies in area of salt movement, which has a close relationship with formation of traps. The distribution of reservoir is controlled by sedimentary facies and structure at the same time,so the key of exploratory potential evaluation is to predict traps and sands distribution correctly.The study idea is to combine geology with geophysics closely, so geology is basic and geophysical technology is means. Taking advantage of seismic, logging and geological data, we can study basin, block and targets sequentially and deeply. Firstly,features of petroleum geology, sedimentation of strata and tectonic evolution have been analysed to get rules of oil &gas pool formation and delimit zones of prospects.According to summary of discoveries and position of Block 18, it is thought that the block is of good conditions of hydrocarbon accumulation, the main controlling factor is matching of sedimentation with structure, and the objective is find area of sand enrichment based on traps identification. Secondly,subtle seismic interpretation is done by calibration of main target horizons and small faults are identified by technology of coherence and time slice. Based on studies above, several favorable structures have been found by structure maps of main target horizons. Sedimentary background is deep water turbidites system. Different electrofacies are delimited by logging data, therefore, different sedimentary microfacies are delimited by combining electrofacies with seismic facies, and distribution in plane is drawn. Technologies of seismic attributions and frequency decomposition are used to predict sand in quantity,and AVO and prestack inversion are used to predict hydrocarbon bearing of reservoir later. Lastly, resource of traps is computed and traps are ranked by comprehensive evaluation.Important products are following: 1) The principal plays in block are salt induced structures, including anticlines, drapes, faulted anticlines, nosing structure, turtleback highs. 2) The main sedimentary types are deep water turbidite, sedimentary microfacies includes channels,bar points and lobe. Salt induced structures control the distribution of deposit and type of microfacies. 3)24 stratigraphic-sturcture complex traps have been found, whose target reservoirs include Oligocene interior sand,Miocene interior sand and Albian carbonate. Most of these traps are highly reliable. 4)By computation in Block 18,OOIP(P50) is 41×108bbl,recoverable resource(P50) is13.6×108bbl. Block 18 has 12 trap I,12 trap Ⅱ and Ⅲ by optimization and rank.5)Block 18 has great exploratory potential, which partions Tertiary prospect area in west and Cretaceous prospect area in east.