Elastic properties prediction for drilling and subsurface evaluation for the Grand Banks and Niger Delta

Yusuf, Babatunde Olaiya (2019) Elastic properties prediction for drilling and subsurface evaluation for the Grand Banks and Niger Delta. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Formation bulk density (RhoB) is an essential parameter which can provide very useful information required for planning the position of a new well and properly characterize a reservoir for effective field development. Several correlations had been developed in the past decades to estimate bulk density. A previous study done using data from the Grand Banks reveal that the prior density-velocity relations could not predict density accurately in the five wells studied. The two major problems with these empirical relationships are: (1) they were developed primarily for clean formations and they have failed to produce reasonable estimates in non-clean/mixed-lithology formations; (2) they are not applicable to rocks that contain micro-cracks/fractures. There is no single model that has dealt with these two problems. In this thesis, a new formation bulk density prediction method that can be applied to clean formations, non-clean/mixed-lithology formations and rocks that contain micro-cracks is proposed. The model is validated with additional laboratory measurements on cores and field-tested with field wireline log data from the Niger Delta and Grand banks basins. The most reliable method of deriving the shear wave velocity is by estimation from compressional wave velocity. Most old wells lack shear wave velocity data and for the wells drilled recently, the need to verify poor quality data makes the development of models very important. A region-specific model is proposed for more accurate derivation of shear wave velocity from compressional wave velocity applicable to the Grand Banks. This model was found to predict better than prior models. Poisson’s ratio is commonly utilized in estimation of fracture pressure. There is need to develop a correlation specific for the Grand Banks. The availability of sufficient well data, a depth trend of Leak-off-test (LOT) data and series of Modular Dynamic Formation Tester (MDT) type data were used to establish a depth trend of fracture pressure and pore pressure profiles to aid successful well planning. The application of outputs from these models and correlations to subsurface reservoir characterization and field development was tested using the Excess Pressure (EP) methodology.

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