Page 345 - Numerical Analysis and Modelling in Geomechanics

326 RESERVOIR COMPACTION, SUBSIDENCE AND WELL DAMAGE
Historical perspectives on compaction and subsidence
Subsidence is an age-old problem and its effects on man and man-made
structures, which range from a nuisance to catastrophic, have been well
documented. 4,5 Subsidence may be caused by the recovery of hydrocarbon
reserves, 6,7 pumping water from aquifers, 8 geothermal fluid withdrawal, 9
mining 10,11 and tunneling. 12 Compaction of oil and gas reservoir rock is the
source mechanism for costly problems in petroleum fields all over the world.
Major problems have been documented in Norway, Russia, Italy, Venezuela,
Japan, and in the United States in California, Texas, and the Gulf of Mexico. 7
For example, reservoir compaction in the Ekofisk field in the North Sea has
reportedly caused subsidence greater than 16 ft, resulting in costs of $400 million
to jack up offshore platforms and repair related damage. 13–21 Reservoir
compaction and casing damage associated with it has also been a continuing
problem in other North Sea fields. 22,23
Extensive and costly problems associated with subsidence and reservoir
compaction in the United States have occurred in the San Joaquin Valley near
the cities of Los Angeles and Bakersfield in Southern California. Reservoir
compaction in the Wilmington field near Long Beach, California, caused
earthquakes, resulted in surface subsidence of as much as 33 feet, and hundreds
of well failures and damage to surface facilities and structures. 24 By 1962, the
problems in the Wilmington field and surrounding areas required expenditures
exceeding $100 million for repairs and damage mitigation. As a result, effort has
been expended towards developing mathematical models of the Wilmington
field. 25–28
The Belridge field in the San Joaquin Valley near Bakersfield, California also
has a long history of subsidence and compaction problems. 29–32 It has been
producing since 1911 and is now recognized as one of the largest oil-producing
reservoirs in the United States. 33 It has well-documented problems associated
with reservoir rock compaction, which are discussed later in this chapter. The
Lost Hills field, also in the San Joaquin Valley in the same geographic location
as the Belridge field, has a history of compaction and well damage problems
almost identical to the Belridge field. 34,35

A problem of scale

Reservoir compaction is often viewed as a large-scale problem. The areal extent
of measurable surface subsidence may be of the order of square miles and the
lateral extent of the reservoir of the same order. Hydrocarbon reservoirs that
have significant compaction and surface subsidence have been thick, of the order
of hundreds to thousands of feet. However, actual compaction-induced surface
subsidence may be of the order of only several inches to a few feet, which may
be sufficient to cause distress to buildings and other surface structures. 36
Moreover, compaction causes significant operational problems for hydrocarbon