Estimation of Land Surface Subsidence Induced by Hydrocarbon Production in the Niger Delta, Nigeria, Using Time-Lapse Orthometric Leveling Data

Abstract

Time-lapse orthometric levelling measurements, acquired in 1988 and 2003 in the south-east Niger Delta basin, are used to estimate surface subsidence resulting from hydrocarbon withdrawal. The value of the subsidence was determined by finding the differences from the orthometric heights in the base and the monitor surveys. The elevation ranges between -30m along river channels and 3m for the base 3D survey while that for the monitor survey shows elevation of -27m to 5m. Hydrocarbon production in reservoir under this area was 89.52stb/day initially and declined to 13.92stb/day, and the reservoir pore-fluid pressure depletion is only 674psi, initially at 3833psi but dropped to 3159psi in 15 years. The results from the analysis show that the rate of land subsidence at each location of levelling varies from 66.67mm yr-1 to 200.00mm/yr with an average of 86.00mmyr-1. When comparing the land subsidence trend, hydrocarbon production and reservoir pressure declines, there is no positive correlation between the three phenomena. This is an indication that land subsidence is localized where the measurements are carried out mainly in river channels and slopes caused by erosion, and not on a regional scale. The results of this work can be used for engineering and environmental works.