RESEARCH OF A RESERVOIR BOTTOM ZONE DESTRUCTION BY FILTERING FLOW OF THE FORMATION LIQUID AND PREVENTION OF CALL FORMATION IN THE WELL

Abstract

The relevance of the study is caused by the need to prevent the formation destruction near the bottom of the wells and the appearance of a large amount of sand in the formation fluid during its filtration into the bottomhole zone of the well. The solution to this problem will improve the work of filtration of formation fluid from the layer into the well and reduce the cost of additional application of methods for stimulating the inflow of formation fluid to the well. The aim of the research is to to develop and propose a methodology that allows, during the operation of wells prone to plugging, limiting the reservoir pressure depression to the maximum permissible value at which the material of the filter zone is in elastic state throughout the entire volume. Objects. To determine the stress state in this section of the string, it is necessary to represent this element in the form of a hollow ball, which rests on the casing string. When the hydraulic pressure in the material of the porous medium for the formation fluid filtration decreases, it will expand in the absence of obstacles to the flow of this process. At the same time, there is an increase in the formation fluid pressure outside the hollow sphere. Therefore, it is necessary to find the regularities that occur during the expansion–contraction of a porous medium in formation fluid filtration through a hollow sphere. Methods. The largest difference in normal stresses occurs on the borehole wall, since the radial stresses are equal to the minimum, and the tangential stresses are equal to the maximum values. Therefore, depending on the reservoir pressure depression and the strength properties of the fixed zone, the following well operating conditions are possible: the fixed near-wellbore part of the formation throughout the entire volume is in an elastic state; the fixed near-wellbore part of the formation throughout the volume is in a plastic state. It is known from the solution of the elastic problem that the largest difference in the normal stresses in the body of a hollow ball during fluid filtration through its wall to the center occurs on the inner surface. Therefore, the conditions for the fluidity of the ball material will arise, first of all, on the inner surface of the ball. Solving the elastic problem, taking into account the compressibility of the rock, it is possible to determine the magnitude of the pressure drop on the formation, which excludes the possibility of plastic flow of the formation material, that is, the permissible pressure drop. Results. When operating wells prone to plugging, it is necessary to limit the reservoir pressure drawdown to the maximum permissible value, when the material of the near-filter zone is in an elastic state throughout the volume. Thus, the maximum difference in the main normal stresses is observed on the borehole wall, therefore, in order to prevent the destruction of the formation near the bottom hole, the necessary condition is the compliance of the strength properties of rocks with the stresses acting in this zone.

Keywords

• deformation
• intensity
• radius
• thickness
• well
• reservoir