Subsidence and the Petroleum Industry: An Overview

Richard F. Meyer, David E. Powley

About 35 oil and gas fields are known to be associated with surface subsidence, the result of fluid withdrawal and consequent pressure drop and reservoir compaction. Such fields are located worldwide, mostly in clastic rocks but also in chalks. The effects mainly are of vertical displacement, often accompanied by some horizontal strain. Subsidence may be caused by tectonism, surface loading and vibration, mineral reactions with water, or fluid withdrawal, but mostly results from extraction of oil, gas, or, most importantly, ground water. Subsidence is measured at the surface through leveling with bench marks and in the subsurface from casing collar depths or with radioactive bullets in borehole walls. Rates of subsidence can be as much as 2 ft/year; surface subsidence com only lags behind cumulative production. Prediction of subsidence can be done rather accurately within a producing field or group of fields, or within the same stratum in a particular province, once the problem is understood, but is very difficult in a frontier area unless carefully considered before drilling. Once recognized, subsidence can be prevented or partially rectified by reinjection to replace extracted fluids, thus restoring formation pressure and consequent compaction. Compaction itself may serve as a production drive mechanism. Subsidence may cause such adverse effects as bent or broken casing, settling of drilling platforms, broken pipelines, and flooding of surface facilities.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.