 |
| Titel |
In-Situ Stress and Fault Reactivation Associate with LNG Injection in the Tienchanshan Gas Field, Fold-Thrust Belt of Western Taiwan |
| VerfasserIn |
Jih-hao Hung, Jong-Chang Wu |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048020
|
|
|
|
|
|
| Zusammenfassung |
| The Tiechanshan gas field located in the fold-thrust belt of western Taiwan was
depleted and converted into underground storage of Liquid Natural Gas (LNG)
decades ago. Recently, CO2sequestration has been planned at shallower depths of
the structure. In this study we intend to characterize the in-situ stresses from over
40 wells and assess the leakage potential through fault reactivation in response to
pore-pressure increase as a result of LNG injection. Formation pore pressures (Pf),
vertical stress (Sv), and minimum horizontal stress (Shmin) were measured from
repeated formation tests, density logs, and hydrofrac including leak-off tests and fluid
injection, respectively. Formation pore pressures are hydrostatic above depths of 2
km, and increase with local gradients of 0.62 and 0.94 psi/ft above and below 3.2
km. Extremely high pore pressures (λp=0.8) are observed at depth below 3.8 km.
Lower than normal pressures (average 0.42psi/ft) are observed in the gas-bearing
reservoir of Talu A-sand. The gradient of Shmin is ~ 0.77 psi/ft or equivalent to
0.74 of Sv (~1.04 psi/ft). Combined the structure contour map of A-sand top with
measured Shmin and Sv,stress state in the Tiechanshan field is a predominantly
strike-slip stress regime (SHmax >SV >Shmin). Without extended leak-off tests and
images of borehole wall, the upper-bound values of maximum horizontal stress
(SHmax) constrained by frictional limits and coefficient of friction (μ=0.6) is about
1.21 psi/ft. Caliper logs from two wells show that borehole breakouts is oriented
~28oN, or maximum horizontal stress being 118oN, which is sub-parallel to far-filed
plate-convergence direction. Geomechanical analyses on the reactivation of pre-existing
faults at the depths of LNG reservoir sand indicate that all faults are relatively stable.
Sensitivity analyses of affecting parameters indicate even the pessimistic risk scenario
would require ~5.9 Mpa excess pore pressure to cause the optimal oriented F1
fault to reactivate. This corresponds to LNG column height of ~760 m (density=
~790 kg/m3), whereas the structure closure of the A-sand does not exceed 400
m. Therefore, LNG injection will unlikely to compromise the F1 fault stability. |
|
|
|
|
|
|