Traditionally effective differential pressure is determined to the maximum of an indicator diagram of flow rate fr om depression dependence. For reliable determination of the depression it is necessary to pass this maximum, significantly having lowered a flow rate and, therefore, to pass into the ultramundane condition of the formation permeability, i.e. to pass a point of no return, a skin factor. Irreversible decrease in the flow rate will remain also in case of the subsequent operation of a well. For elimination the skin factor is offered a new method of the maximum allowable depression determination not in the formation of the drilled exploitation well, and on the core, which is selected fr om this formation in earlier drilled next test hole and stored in the core storage (core storage time is unlimited). The method is implemented by removal of elastic waves distribution time dependence in the core sample fr om pore pressure in a hydropressure chamber with confining pressure, approximate to the reservoir under the conditions of its natural occurrence, and subsequent pressure estimating of the most admissible depression upon the formation on "memory" by a core pressure of the maximum paleo-immersion of formation layer in the period of their progressive epigenesis. Measurements are taken smoothly, reducing pore pressure to formation with a speed which isn't exceeding the speed of a relaxation rate of ultimate stress lim it in the core, of which judge by acoustic emission absence – acoustic noise from mutual sliding of grains with formation crackling in the course of a core plastic deformation, in case of which there is a repacking of grains to consolidation of formation pore space and corresponding reduction of its permeability. At first sharp reduction of a change gradient of this dependence in case of plasticity lim it achievement and acoustic issue emergence judge about the value of the maximum allowable depression. This plasticity lim it means the achievement by the core of the stress condition, corresponding to the maximum depth of a paleo-immersion of formation layer.
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