Predicting the potential for induced earthquakes due to long term oil/gas production in the Niger Delta basin, Nigeria

Publication Date : 23/05/2022


Author(s) :

Abija, F.A, Abam, T.K.S, Teme, S.C, Eze,C.L.


Volume/Issue :
Volume 58
,
Issue 1
(05 - 2022)



Abstract :

Production induced reservoir pressure dissipation causes stress changes leading to reduction in magnitude and rotation of the horizontal stresses on fault planes. Abrupt, stick-slip and spontaneous shear displacement of the downthrown block on crustal faults which can be due to stress perturbations is the causative mechanism of induced earthquakes in energy production. In this studies, production induced depletion has been estimated as percentage of predicted reservoir pore pressure at the well-fault plane interface in a horizon interval of 3500 – 3980m. The structural attitudes of three representative fault planes were also measured from depth structure map and dynamically derived in situ stresses determined. Fault reactivation tendency was assessed based on the Coulomb - Mohr and composite Coulomb - Griffiths fault strength criteria to determine the optimal window for critically stressed and optimally oriented faults for slippage. The static frictional coefficient of the reservoir bounding faults vary from 0.43 – 0.46, 0 phyllosilicate cataclastic infilling suspected for the low values. The horizontal stress orientation rotated through 3.2 0 0 0 to 17.5 causing the new orientation of the maximum horizontal stress to rotate through 108.22 to 122.5 and the 0 0 minimum horizontal stress rotated through 18.22 at 10% to 32.5 at 99% reservoir pressure dissipation on the frictionally unstable fault plane 1. The magnitude of the maximum horizontal stress reduced from 51.2mPa to 41.5mPa and minimum horizontal stress from 36.1mPa to 26.0mPa at 99% reservoir pressure depletion. Predicted potential for induced earthquakes increased with depletion as the optimal fault reactivation window widened from 0 0 0 0 78.1 and 36.1 under in situ conditions to 77.1 and 37.5 for all steeply dipping faults with poles within the window and parallel to the maximum horizontal stress to reactivate and generate felt seismicity. A wider window at full reservoir depletion imply possibility of increased number of faults and their potential risk of slippage. Injection in water flooding operations to maintain reservoir pressure as well as enhance hydrocarbon recovery is recommended


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