Principal Component Analysis of Seismic Data and Reservoir Sequence Stratigraphy: Powerful Allies in Reservoir Modelling and Waterflood Management, Gbokoda Field, Nigeria

By

Stan P. Franklin¹, Steve Jenkins¹

(1) Chevron Nigeria Ltd, Lagos, Nigeria

 Principal component analysis (PCA) of seismic data, combined with reservoir sequence stratigraphy, creates a powerful method for mapping and modelling pressure compartmentalization. Understanding compartmentalization during waterflooding is key to locating water injectors and producers to maximize sweep efficiency.

Gbokoda Field is located onshore Niger Delta and contains over 850 mmb oil-in-place. The main A-05 reservoir is a shoreface sandstone and was placed on peripheral waterflood during primary development due to anticipated weak aquifer support.

After 3 years of waterflooding, our pressure surveillance program indicated pressure compartmentalization with ~350 psi of differential depletion across the field. Several western wells ceased production due to low tubing pressure, despite good injection from a horizontal injector downdip. In contrast, the eastern portion of the field showed minimal depletion. Analysis of the log and seismic data within the western area showed a poorly expressed incised channel.

Starting with Gbokoda 3D seismic data, we used PCA to perform seismic curve shape comparison to group the different curve shapes into mappable clusters. Amplitude and phase form the largest contribution to the variance of the clusters. Clusters represent different rocktypes, facies, and fluids creating high-resolution mappable units.

By combining the PCA-based mapping with log and core-based sequence stratigraphy, we determined the producers were located within the shoreface sequence, whereas the injection well was located within a disconnected incised valley fill sequence.

After updating our simulation model, we restored production and reversed the pressure depletion by reactivating the producers and completing a new horizontal injector within the shoreface sequence.