51st U.S. Rock Mechanics/Geomechanics Symposium,
San Francisco, California, USA
2017. American Rock Mechanics Association
1 in the last 30 days
61 since 2007
Show more detail
ARMA Member Price:
ARMA Non-Member Price:
ABSTRACT: In unconventional reservoirs, where oil or gas is produced from ductile shales, understanding time-dependent geomechanical phenomena, like creep and stress relaxation, may be crucial for the successful development of a play. Laboratory creep data is always limited in time and therefore a creep compliance function is needed to extrapolate laboratory findings and to model long-term behavior.
In this paper, we present a comparison of regression methods, using creep data of shale samples from the Baltic Basin, Poland. Creep data used for the analysis consists of three 72-hours-long tests and one two-week-long test. Differential load was applied in steps, the last one lasted for 39 hours in case of shorter tests, and 303 hours for the longer test. In order to describe the uncertainty of every method, we fitted parts of the data of different lengths, and then extrapolated the fitted function to the entire time span of the data.
While self-similar functions such as the power-law and logarithmic function are useful for the relatively few parameters required to describe creep behavior, Prony series give better fit to laboratory data by 1 to 2 orders of magnitude in least-squares sense. However, the caveat of the Prony series is that the choice of retardation times is not necessarily unique. Although Prony series with different sets of retardation times may fit a data equally well, these may predict completely different results when extrapolated to larger times beyond the laboratory experiment. In this paper we investigated wide spectrum of retardation times, and the parameters obtained from inversion.
Shales may have diverse lithological composition, compaction level, but their common feature is high clay content and very low permeability with relatively high porosity. Time-dependent deformations, even at constant and small load, are caused by a delayed microstructural deterioration, known as cataclastic creep (Fabre and Pellet 2006). Also, clay platelets and grains may undergo sliding and rotation followed by aggregate deformation. These phenomena are slowed down by friction and thus appear viscous. Creep is an inelastic phenomena, and often is neglected in reservoir analysis. The inverse of creep strain is stress relaxation. In bigger scale, when ductile shales are loaded tectonically, they exhibit instantaneous elastic response, followed by long-term stress relaxation. It can change significantly the in situ stress state in the reservoir.
Number of Pages
Looking for more?
Some of the OnePetro partner societies have developed subject- specific wikis that may help.