3-D Seismic Attributes Analysis And Reserve Estimation Of “Guramala Field”, Coastal Swamp Depobelt, Niger Delta.

ABSTRACT

An integrated seismic interpretation using 3-D seismic data, check shot data and a suite of well logs for four wells were analyzed with the Petrel (seismic to simulation software). The objectives were to carry out a detailed formation evaluation, reservoir characterisation and a 3-D assisted structural interpretation of the densely faulted oil field in the coastal depo-belt of the Niger Delta. RMS amplitude, instantaneous frequency map and interval average extraction maps were extracted on the surfaces which revealed the bright spots and Dim spots on them. The attributes were used to establish the diagnostic ability of 3D seismic attribute analysis in enhancing seismic interpretation, and the importance of petrophysical analysis in economic decision in E&P companies as well as researchers of the mid Miocene to Pliocene, Agbada Formation reservoirs in the coastal swamp depobelt of the Niger Delta basin. The method adopted involved a delineation of the various lithologies from the gamma ray log, identification of reservoirs from the resistivity log, well correlation, determination of petro physical parameters, horizon and fault mapping, time to depth conversion, attribute analysis and reserve estimation. Two reservoirs named Sand_A and Sand_B were mapped. The petrophysical analysis gave porosity values of reservoir Sand_A ranging from 18.1-20.3% and reservoir Sand_B ranging from 13.10-14.9% across the reservoir. The permeability values of reservoir Sand_A ranged from 63-540md while for reservoir Sand_B it ranged from 18-80md. The Sw values for the reservoir ranges from 38-42% in Well 2, 35.39-68.79% in well 7, 32.28-45.57% in well 9 and 68.79-96.06% in well 11.The volume of shale range from 17-82% across the reservoir Sand_B and 49% in reservoir Sand_A. Seven faults labelled F1, F2, F3, F4, F5, F6, and F7 and Four horizons were mapped. Depth structure maps generated showed a massive Northeast-Southwest trending anticlinal structure. The Reserve estimation was calculated using the empirical formular method with the petrophysical parameter, hence well 2 has 9.3 mmbls, well 7 has 5.7mmbls, well 9 has 3.5mmbls and well 11 has 2.3mmbls. The petrophysical analysis revealed the presence of oil with a volume that is however not favourable for commercial exploitation. These techniques proved to be very reliable and useful in reservoir characterization and formation evaluation.