Basic physical and mechanical properties of rocks

Drill holes are drilled in a wide variety of geological conditions. The way of destruction of rocks, the type of rock cutting tool, the mode of its operation is chosen depending on the physical and mechanical properties of rocks, which are determined by a complex of geological features: mineralogical composition, structure, texture and others.

Mountain rocks are called natural accumulations of minerals that have arisen as a result of certain geological processes in the earth's crust. Therefore, many properties of rocks will depend primarily on the properties of the minerals themselves, their chemical composition, the shape and size of the mineral particles, location in space, the nature and strength of the bond between the particles, the conditions for the formation of rocks and their structure.

The genetic classification of rocks by composition, adopted in geological studies, taking into account their origin (magmatic, sedimentary, metamorphic) is presented in a reduced form, as a prerequisite for the characterization of rocks according to physical and mechanical properties. The properties of rocks affecting the drilling process are very diverse. There are physical and mechanical properties of rocks. They express and evaluate using certain indicators (characteristics).

Physical properties of rocks

Physical properties characterize the physical state of rocks, i.e. Qualitative certainty, manifested in their density, humidity, porosity, fracturing and weathering in natural conditions. Data on these properties make it possible to qualitatively evaluate the strength and stability of rocks.

Mechanical properties of rocks

Mechanical properties of rocks determine their behavior under the influence of external forces - loads. They are manifested and directly evaluated by the strength and deformability of rocks. Indicators of mechanical properties are used for various engineering calculations, for example, in calculating the sediment of structures, determining their drillability, etc.

Basic physical and mechanical properties of rocks

The physical and mechanical properties of rocks in the sample always differ significantly from their properties under natural conditions. In the rock massif, as a rule, they are more heterogeneous in composition, structure and physical state and are more anisotropic in properties. This is due to the fact that rock massifs usually have surfaces and zones of weakening, they are significantly and unevenly fissured and weathered, texture attributes (stratification, schistosity, banding, etc.) are more pronounced in them, they are often broken by tectonic movements and have different stress states depending on the position in the geological structure of the area.

Structure of rocks

Practical data of core drilling confirms the closest dependence of physical and mechanical properties of rocks on their structure, the size of rock-forming minerals, the quantity and quality of the mineral composition of cement. Practical data of core drilling confirm the closest dependence of physical and mechanical properties of rocks on their structure, the size of rock-forming minerals, the quantity and quality of the mineral composition of cement.

The mechanical properties of a rock as a solid are directly related to its structure (structure), with molecular forces of cohesion.

By the structure of a solid rock is meant the structure of the substance of the rock, which is a cluster of individual crystals and their fragments of various sizes. The structure of the rock is characterized by a pattern of distribution of crystals of grains and cement in size, the conditions for their coalescence and mutual arrangement.

The cleavage planes in graphite, mica, gypsum, rock salt, calcite can be clearly expressed in individual crystals that make up the rock. In a direction parallel to the cleavage plane, the crystal has the lowest tensile strength, since the distance between these planes in the lattice is much larger than between any other planes.

For the strength of rocks characterized by its dependence on the size of the grains that make up the rock minerals. Mineral grains of small dimensions have a much greater relative mechanical strength than large particles. This pattern extends to the rocks. Fine-grained rocks have higher mechanical strength and lower drillability than coarse-grained.

Drilling of rocks

By the term "drillability" it is customary to understand the complex characterization of a rock, consisting in the ability of a rock to resist penetration of a rock cutting tool into it during drilling.

Drilling of rocks is a function of many variables, depending on natural, technological and technical factors. The drillability of the rock depends on its physical and mechanical properties, on the shape, size and material of the rock cutting tool, on the drilling regimes used (the rotational speed of the drilling rig, the axial load on the rock cutting tool, the quality and quantity of the washing liquid), etc. It is therefore natural that the drillability of the rock is determined separately for each type of rock cutting tool.

Methods for determination of rock drillability

There are a number of objective methods for determining the drillability of rocks, which have found application in rotary and shock-rotational drilling methods. The main such methods include the following:

  • The TsNIGRI method is the determination of the rock categories from drillability on the basis of their abrasiveness and dynamic strength in a combined expression
  • WITP method - determination of rock categories by drillability with the help of the VITR-OT device (determinant of rock drillability)
  • The method for determining the actual rock drillability by means of experimental drilling with rational values of drilling mode parameters and rational types of rock cutting tool
  • The first two methods of determining the rock drillability are recommended to be used as control methods. For the technical standardization of geological prospecting drilling, a method of determining the rock drillability by actual data should be applied.

Classification of rocks

In the process of generalizing the experience of drilling various rocks, mastering new drilling methods, changing techniques and drilling technology, the classification undergoes certain changes and refinements. Therefore, in a number of classifications, the quantitative indicator of drillability is absent, and the rocks are assigned to one or the other group by their petrographic characteristics.