In order to inject significant volumes of drill cuttings and fluids into an unconsolidated formation, it is necessary to fracture the formation. A number of injection mechanisms are possible; and the dominating mechanism depends on the physical properties of the formation as well as other factors. The experimental investigation conducted during the study reported here indicates that rock texture is a key, contributing factor in certain physical rock characteristics including velocity and load bearing strength.
Rock physics laws relate porosity, mineralogy, saturation, and pore-fluid to elastic rock properties, to elastic-wave velocity, and to impedance. These laws describe, for instance, the connection between seismic impedance and velocity and bulk reservoir properties.
Often, an earth volume under examination has to be described by more that one rock physics law: Different depth intervals may have distinctively different velocity-porosity trends due to variations in depositional and diagenetic history. When building a rock physics model, one has to single out various velocity-porosity trends from the entire volume of data and assign these separate trends to appropriate depth intervals and depositional sequences. This procedure is called rock physics diagnostic. It is typically conducted on well log and core data. Rock physics diagnostic yields useful relations between seismic observables and porosity. It also leads to a description of the texture of rock, as shown in this paper. The combination of rock physics with stratigraphy provides a basis for interpreting seismic data away from a well. This combination also forms the basis, in a 3D volume, for predicting porosity and the types of fluid present, and for estimating strength.
In order to dispose of significant volumes of drill cuttings and fluids into an unconsolidated formation, it is necessary to fracture the formation. A number of injection mechanisms are possible; and the dominating mechanism depends on the leak characteristics of the disposal formation, the direction of minimum principal stress in the formation, the injection sequence of the cuttings, and the physical properties of the formation. This paper focuses on the strength and sonic properties of shaley sandstone Static and Dynamic Properties of Shaley Sandstone
For this purpose, new laboratory data have been obtained on a sandstone core with large amounts of clay. The core was taken from the depth interval 10118 ft to 10197 ft.
The data have been analyzed, first, to establish relations between the static and dynamic elastic moduli of the rock and its failure characteristics. Relations have been established between the static Young? modulus and Poisson? ratio on the one hand and the dynamic shear modulus on the other hand. These relations allow one to predict the static moduli from velocity well log data. The relations are
E_Static = -0.34 + 0.59 G_Dynamic; R= 0.96
PR_Static = 0.37 0.0208 G_Dynamic; R-0.99
where E_Static and PR_Static are the static Young's modulus and Poisson's ratio, respectively, and G_Dynamic is the dynamic shear modulus. The quantity "R" refers to the correlation coefficient for these two relationships based on the experimental data. All moduli are in GPa. The dynamic shear modulus is the product of the bulk density times the shear-wave velocity squared (Figure 1). We have also found that the failure envelope for the samples can be modeled by the Drucker-Prager and CAP models. Either the CAP equation or a linear equation can approximate the hardening law. Both are fairly close to each other in the case under examination. The resulting fixed and moving yield surfaces
