ON THE DESTRUCTION AND PREFRACTURING OF SOLID ROCKS UNDER BLASTING IN FORMATION CONDITIONS

Abstract

Purpose and task. Analysis and specification of mechanisms of softening and change of structure of monolithic and low-fractured rocks under blasting of single and dispersed charges, definition of the reasons and model of their evolution in a formation. To solve this goal, the followingscientific tasks were set in the work:1. Estimation of force factors of external action on rock.2. Thermodynamic analysis and detection of mechanisms of structural changes in rocks at a considerable distance from the well, which provide a change in its productivity.Research methods. To solve the set tasks, the following were performed: calculations of the attenuation of shock wave amplitudes generated during the explosion of spherical and elongated charges; analysis of the results of explosive treatments of oil and gas wells; energy analysis of processes and mechanisms of changes that occur around the well in the reservoir.The main results. Studies have shown that structural changes in rocks during low-energy explosions, as well as other low-energy methods of external action on the reservoir occur in the form of increased cracking of rocks at micro and macro levels due to cooperative effects of external action, internal reservoir energy and physico-chemical effects of reservoir fluids.The main results. The mechanisms of decompaction of the rocks in rock formation conditions in the presence of rock and reservoir pressure at low-energy external actions are considered. Experiments on the operation of oil, oil and gas and gas wells show that the transition of the system "well - formation" from one thermodynamic state to another occurs in a time that depends on the internal energy of the formation. The transition is the result of the cooperative effects of the combined action of external influences, the internal energy of the formation and rock pressure. For gas wells this time does not exceed a few hours or days, for oil and oil and gas with depths of 3000… 4000 m the typical time of the well to reach maximum productivity is ≈ (30 - 90) days.Conclusions and practical significance. The analysis of the results of industrial tests of explosive intensification technology and calculations of attenuation of compression wave amplitudes show that under rock pressure conditions structural changes in rock after explosions of several charges occur at distances up to ≈ (80… 100) R0. Under reservoir conditions, the main reasons for the appearance of such long zones of increased permeability around the well are the cooperativeeffects of the combined action of blast waves, reservoir gases (methane, carbon dioxide, helium and possibly hydrogen), as well as changes in rock pressure in the process of its development. Of practical importance is to understand the sequence of technological operations in the work tointensify the inflow of oil and gas.