THE SUBSURFACE STRUCTURES IN KOCR FIELD IN THE NIGER DELTA, NIGERIA, USING 3D SEISMIC TIMELAPSE DATA

Igwenagu Chinyere L,Amakiri Arobo R.C,Uko Etim D,Tamunobereton -Ari I

doi:10.26480/gbr.01.2021.07.12

Abstract

The subsurface structures in KOCR Field, in the Coastal Swamp Niger Delta, Nigeria, are here presented, using seismic 3D timelapse. The KOCR Field lies on latitudes 4o50’58’’-4o55’19’’N and longitudes 6o18’41’’- 6o26’41’’E with aerial extent of 840km2. The base (1997) and the monitor (2009) seismic surveys resulted in a 4D response difference. The Base and Monitor data have a root-mean-square repeatability ratio (RRR) of 0.38 implying a very good repeatability when considering the acquisition, processing and environmental noises. Data processing and interpretation were carried out using Petrel software. The average thickness of the reservoir is about 69m at the depth of 3932m. Reservoir pressure decline rate of 0.062psi/day resulted in production decline rate of 1192.21bbl/day. Structural interpretation of seismic data reveals a highly-faulted field. Fault and horizon interpretation shows closures that are collapsed crestal structures. All the interpreted faults are normal synthetic and antithetic faults which are common in the Niger Delta basin. The lengths, dips and orientations of the faults and horizons, in the base and monitor stacks, are equal indicative of no faults reactivation that could have resulted from hydrocarbon production. The results of this work can be used in reservoir, field and environmental management in the area of study.

Highlights

In Time-lapse seismic, the difference between two seismic vintages acquired at different time intervals under same acquisition conditions gives information on the variation of geophysical properties due to the hydrocarbon production
Structural interpretation of seismic data revealed that the field is highly faulted with synthetic and antithetic faults which are in line with faults trends identified in the Niger Delta
The following conclusions are made: (i) Production decline of 1192.21bbl/day resulted from pressure decline of 95.50bar/year or 0.062psi/year. (ii) Most of the data points were not repeatable as evidenced in the computed Normalized root mean square (NRMS) of 0.38 meaning that on 62.0% of Base and Monitor data points were coincident

Summary

Introduction

In Time-lapse seismic, the difference between two seismic vintages acquired at different time intervals under same acquisition conditions gives information on the variation of geophysical properties due to the hydrocarbon production. Reservoirs producing oil or gas are subjected to pore pressure depletion. This creates changes in the stress and strain fields of the rock material both inside and outside the reservoir. In addition to leakage of hydrocarbons, hazards are associated with wells crossing reactivated faults. Reactivated faults can have close relationship with earthquakes. The results of the work can be applied in the hydrocarbon exploitation scheme to minimize the damages associated with production, and to ascertain reactivation of faults in the area study

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Results

Conclusion