ABSTRACT:
When sands are buried in sedimentary basins the additional overburden mechanically compact the sands to a denser configuration. Burial also increases temperature and the porosity is reduced by chemical compaction. Therefore, the geomechanical behavior of sandstones is to a large extent controlled by mechanical and chemical compaction. To investigate the relationship between the geological processes and geomechanical properties we conducted rock mechanical tests and petrographical analyses on different sandstones from the North Sea. For all tested sandstones with different degrees of cementation the peak strength is closely correlated with the Young’s modulus. There seems to be a strong correlation between porosity and strength. This correlation was further improved by taking into account the primary layering. Sonic travel times also correlate with the peak strength and can be used as a method for calculating rock strength.
1 INTRODUCTION
1.1 Introduction
After sands are deposited they become sandstones during the geological history. The main driver for this process is the porosity reduction in the sand caused by deeper burial. Understanding the effect geological history has on the strength and deformation properties of sands is important. For example, the oil industry needs to plan and conduct safe drilling, design completions and manage sand production. The objective of this paper is to investigate the relationship between geological processes and geomechanical properties. A rock mechanical test program and petrographical analyses of different sandstones from the North Sea were conducted.
1.2 Sandstone diagenesi
s When sand is deposited it usually has a porosity around 35-50% dependent on the initial sorting of the sand, mineralogy content and amount of fines (Bjørlykke 1989). During burial these sediments experience porosity reduction in the form of sediment volume reduction or increase in bulk density due to mechanical and chemical compaction.
