The purpose of the paper is the presentation of the geomechanical approach to the development and the improvement of methods for increasing well productivity and reservoir recovery. Control stress-strain state in the vicinity of a well to enhance the permeability of the well drained zone increases significantly efficiency of stimulation of a well. It is carried out by directed unloading of the reservoir on the basis of knowledge of the deformation, strength and filtration properties of specific field rocks. Examination of rock mechanical properties is made by laboratory tests of rock samples at the true triaxial apparatus. The methodic and the results of laboratory studies of rocks and of pilot field works on wells are presented on the example of a specific field. They have shown high efficiency of this approach.

1 Introduction

As the result of mudding while drilling, siltation of a reservoir during the operation, plastic deformation of rocks under the influence of shear stresses, wells are often surrounded by poorly permeable zone. In addition, efficiency of many widespread EOR methods, such as acid treatment, hydropulse impact, is caused by the existence of a good hydrodynamic link between the reservoir and the well.

The permeability of well drained zone can be restored by a simple and effective way – by creating a new artificial system of filtration channel by rock cracking using directional unloading reservoir. This method, known as the "geoloosening method" (Khristianovich et al. 2000), has successfully passed pilot field tests, and is based on the capability of majority of rocks to fracture and to disintegrate in case of the emergence of certain level shear stresses. The required stress state can be created by decreasing the pressure in the well, combined with certain operations, intended priory to form a bottom geometry (more perforation, slot cutting, etc.). The value of pressure drawdown and bottom hole design can be established by the direct physical modeling of the conditions that occur near the well. For this purpose, the Triaxial Independent Load Test System was created at Institute for Problems in Mechanics of Russian Academy f Science. It is a unique research complex that allows using rock specimens to recreate any stress conditions, arising in the reservoir during any process operations in the well and to study their effect on permeability. Tests are carried out on rock specimens, extracted from the particular reservoir core. The facility is equipped with the automatic control system, which allows to set the required loading program and to conduct control as by force and by displacement. Loading trajectories are determined based on calculations: in simple cases, such as simulation of the conditions in the vicinity of the open borehole – analytically, in more complex cases – numerically.

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