Mechanical rock properties

Fractures are important for fluid flow in oil, gas, and water production and geothermal processes. In such cases, the fluids are stored mainly in the matrix porosity but produced primarily using fracture permeability. Fractures penetrating impermeable shale layers create hydraulic conductivity and can develop a reservoir. Artificial fracturing (hydrofrac) can create new fractures or magnify existing fracture. On the other hand, fractures significantly reduce mechanical rock properties. 

Increasing effective pressure compresses the pore space, reduces the pore cross-section area, and closes pore throats and fractures. Therefore permeability decreases with increasing effective pressure. The magnitude of the change depends on mechanical rock properties pressure dependence is strong in weak-consolidated rocks or fractured rocks, for more competent rocks the pressure dependence decreases. A theoretical model was developed by Sigal (2002). 

Despite the common assumption of fault sealing in hydrocarbon fields, very few faults have been characterised in the detail needed which allows identification of the sealing mechanism or controls. Without the construction of a robust set of case histories from such analysis, future seal evaluation will remain a high risk venture. These case histories are also needed to integrate seal behaviour with pressure test, production and in situ stress analysis. The paper has highlighted the importance of an integrated approach from micro to macro and stressed the value of core-based studies to quantify fault rock properties, sub-seismic fault populations and sealing mechanisms. 

Furthermore, the undersaturated nature of the petroleum is suggested not to be primarily controlled by the maturity of the source rock, but rather by the cap rock properties (Sales 1997) and the burial (pressure) history of the accumulation. The same mechanism is suggested to cause more shallow fields in the area to maintain a black oil preference as lower boiling compounds are rapidly leaking from the relatively poor seals. 

The task for the DECOVALEX research teams was to predict the THM effects in the buffer material inside the test pit and in the surrounding rock, both during excavation of the test pit and the heater testing. The test case was divided into three main tasks Tasks 2A, 2B. and 2C. Task 2A was to predict the HM effects in the rock cau,sed by the excavation of the test pit. Geometrical, mechanical and hydraulic rock properties, as well as hydraulic conditions before excavation, were given to the research teams, and they were asked to predict water inflow distribution in the test pit. Task 2B was a model calibration of rock and fracture properties and the hydromechanical boundary conditions, based on actual measured results predicted in Task 2A. Task 2C was to predict the THM effects in the rock and buffer during the heating experiment. The rock model was presumed to have properties based on the calibration in Task 2B. with the calibrated permeability distribution in the near-field rock. At... 

Table 1. Rock properties used for mechanical calculations.

The material properties are given in Table 1. Except for permeability, the properties of the high-permeability zones (Lamprophyres) and the surrounding rock are the same. The mechanical rock-mass properties are obtained from the geological description of the GTS (Keussen et al., 1989). Significantly, the Young s modulus of the rock mass was reduced to 70% of its value for intact rock. 

An extensive examination of the fracture network and mechanical data has been undertaken to determine models of the fracture characteristics of the three formations, the uncertainties in the parameterisation of the models, and the sensitivity of the upscaled flow properties to the underlying parameter variations. The methodology used to calculate effective hydraulic conductivity values and their sensitivity to the small-scale model is described in Blum el al. (2003). The study undertaken to obtain the effective hydraulic conductivity under different stress conditions and presented in Blum et al. (2003) revealed that the important parameters in modelling HM processes in the fractured rock mass are the fracture density, the mechanical (M) properties and the M property variations through the rock mass. 

Baecher, G. B., N. A. Lanney and H. H. Einstein. 1977. Statistical Description of Rock Properties and Sampling, Proceedings of the 18th U.S. Symposium on Rock Mechanics, American Institute of Mining Engineers, 5C1-8. 

Properties of clays and clayey rocks, and also the processes in them depend on a number of factors. Then the mathematical simulation of the properties and processes, as one of the methods of their examination, is a rather difficult problem. Physically it is clear that the speciflc properties of clay rocks (low permeability, plasticity in moist condition) are caused by the existence of clay minerals in their composition, and these properties are a manifestation of surface capacities, which exist between particles of the clay minerals, which are included in the composition of clays. The most useful conception of the activity of surface capacities is the conception of disjoining pressure between colloid particles, Mitchell (1976). In this work we provide a description of the physical and mechanical clay properties and transport processes in them. The description is based on methods of theory of filtration consolidation. Nikolaevskiy (1996), and also on the theory of stability of lyophobic colloids (theory of Deijaguin-Landau-Verwey-Overbeeck, or DLVO theory), which uses the conception of disjoining pressure. 

Rock Mechanics. The properties of rock become relevant when it is used as the foundation of a high-rise building or a large dam. It is also relevant when one examines the stability of the slope of a mountain or a tunnel. It is also the subject of study for the occurrence of earthquakes. 

One of the most common accepted methods of investigating empirical relationships between rock properties such as durability and physical and mechanical properties is simple and multiple regression analyses. In this study, we have used the multiple regression analyses for assessing the samples durabihty using porosity, uniaxial compressive strength, point load index and P-wave... 

Table 5.3 summarizes some polymer retention data from displacement experiments for partially hydrolyzed polyacrylamides. Retention varies from 35 to about 1,000 Ibm/acre-ft over a wide range of fluid and rock properties. Information on converting retention values from pounds per acre-foot to micrograms per gram of rock is given as a footnote in Table 5.3. Several trends are present in the limited amount of retention data in the literature. Fig. 5.22 shows the variation of polymer retention with brine permeability at ROS. The retention at low permeabilities is large and is probably a result of excessive mechanical entrapment of polymer molecules in small pores. Another possible explanation is high clay content. Polymer concentration appears to have little effect on retention for the data shown in Fig. 5.22. The weak concentration dependence in Fig. 5.22 is reinforced by data from Shah for the retention of partially hydrolyzed polyacrylamide on Berea core material shown in Fig. 5.23. Retention at 50 ppm polymer concentration is 77% of the retention at 1,070 ppm.

Fillers of mineral origin are used for a variety of purposes to affect physical, mechanical, electrical properties, and the appearance. Almost every crushed and ground rock may be compounded with UP resins. Hard carbonates such as calcium carbonate, nonreactive sulphates such as barium sulphate (baryte), and some metal oxides are used as fillers, and they result... 

The study of elastic wave attenuation particularly in sedimentary rocks carries information about rock properties and is important for the design of seismic investigations. The mechanisms and relationships to extract information from attenuation parameters are not yet fuUy understood and still a problem. 

Geomechanical rock properties are a specific group of petrophysical parameters, directly measured in rock mechanics laboratories or by specific field tests. But they are also more or less strongly correlated to other petrophysical parameters (for example velocities of elastic waves) and therefore an indirect derivation from geophysical measurements is the subject of research and application. With respect to this application of geophysical methods, we can distinguish between ... 

In the low-frequency range (<1000 Hz), the dominant mechanism is the ionic charge associated with the electrical double layer that exists at the mineral-fluid interface (Binley et ah, 2005). This is also the case for porous sandstones or sand with a quartz-fluid interface. The effect therefore is related to rock properties like specific internal surface, grain, or pore size and in a further step to permeability. 

Rock Mechanical Properties. In the previous section (Figure 4-313), the wear of the bit teeth can be determined in shales by plotting the dimensionless bit torque (T, ) versus the dimensionless ROP (R,). By introducing a new parameter, namely the apparent formation strength, the bit effects can be separated from the lithology effects. 

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