Isotach formulation of the rate type compaction model for sandstone

• New formulation of the Rate Type Compaction model based on the isotach concept.
• Rate Type Compaction Model explains loading rate dependent compaction behaviour.
• Rate Type Compaction Model can be used to simulate multiple loading rate experiments.
• Good agreement between laboratory experiments and Rate Type Compaction Model.

This paper presents a new formulation of the Rate Type Compaction Model (RTCM) for sandstone based on the isotach concept. The RTCM was originally developed to explain the loading rate dependent compaction behaviour observed in laboratory tests on unconsolidated and consolidated sandstone samples and the delayed subsidence behaviour above depleting reservoirs. The original RTCM equation has the limitation of being unable to describe transitions between different loading rates, including the transition to a loading rate of zero (creep). The new formulation combines the features of the original RTCM with the isotach concept developed in soft soil geotechnics, which enables transitions between different loading rates, thereby overcoming the limitations of the original RTCM. The isotach formulation of the RTCM model is used to simulate a multiple loading rate experiment on a Rotliegend sandstone core sample. The agreement between results of the lab experiment and the proposed isotach RTCM model is excellent.