Analysis of the mechanism of cyclic geomechanical treatment to increase well productivity in carbonate reservoirs

Methods for creating microfracture zones (loosening of reservoir rock) in well vicinity by significant reducing pore pressure and techniques for increasing well productivity based on these methods have been actively developed by Russian Academy of Sciences institutes over the past decades. A prerequisite for the application of such methods is the creation of a depression of sufficient magnitude and duration in wells to form man-made microfractures. The paper discusses cyclic geomechanical treatment (CGT), one of the methods for increasing the productivity of oil wells in carbonate reservoirs based on the creation of a deep depression in a well. Effective planning and application of such methods requires understanding the mechanism of microfracturing in the vicinity of a well when a critical pore pressure reduction value is reached. The aim of this study is to substantiate the geomechanical mechanism of microfracturing formation consistent with the results of laboratory studies of core samples and the application of CGT and related methods in wells. The objectives of the study included analyzing the characteristics of laboratory experiments and their results, identifying possible mechanisms and criteria for the formation of microfracturing, and conducting coupled hydrogeomechanical modeling with an assessment of the characteristic dimensions of the affected area. It has been shown that the results of the laboratory experiments and experimental application of the CGT method are inconsistent with the shear failure mechanism, but can be explained by the compaction failure mechanism. Coupled numerical hydrogeomechanical modeling of the pilot CGT application in a well was performed with an assessment of the compaction failure criteria parameters based on core data. The estimated radius of the stimulation zone was approximately 7 m, with the estimated increase in the productivity index to be consistent with actual data.