Perspectives for Re-Stimulation of Horizontal Wells with Multistage Hydraulic Fracturing With Ball Arrangements

Abstract

Abstract The volume of drilling horizontal wells with multistage hydraulic fracturing (hydraulic fracturing) in Russia is increasing annually. According to statistics, at the company's licensed sites, drilling with multi-stage hydraulic fracturing currently accounts for over 70% of the volume of commissioning of new wells and sidetracking. The main reason for the growth of wells with multistage fracturing is a decrease in the quality of the reserves structure, the commissioning of low-permeable reservoirs, and a decrease in effective oil-saturated thicknesses in new areas. Currently, the share of horizontal wells with multi-stage hydraulic fracturing in an enterprise exceeds 25% of the existing fund. Wells with cementless multi-section shanks with ball-activated couplings for multistage hydraulic fracturing (ball arrangements) account for 97% of the well stock with multistage hydraulic fracturing. Hydraulic fracturing couplings and insulating annular packers (swellable, hydromechanical) are installed in the liner layout and are lowered into the horizontal wellbore. Further, during multi-stage fracturing, the couplings are activated alternately by dropping balls of different diameters (with an increase from small to large). The ball arrangements described above are disposable and have an uneven cross section after multi-stage fracturing. This multistage fracturing method is widespread, since it has a high speed of work and has no restrictions on the depth of the well. However, unequal borehole cross-section restricts access to the horizontal wellbore, and there is a need for drilling operations (milling) of couplings immediately after hydraulic fracturing or during well operation. The result of monitoring the flow rate of oil wells with multi-stage fracturing showed a decrease in productivity in the range of 55-75% for the first 2 years. In most cases, repeated stimulation is necessary, as there is a loss of productivity due to contamination of the fractures with process fluids and a deterioration in the conductivity of the hydraulic fracture (rock removal, plugging of the pore space of the fracture). For directional wells with hydraulic fracturing (Economidеs M. et al., 2004), there is a well-known method of restoring productivity - repeated hydraulic fracturing (re-fracturing). In the case of hydraulic wells with multi-stage fracturing with single-use ball arrangements, one of the problems is the selection of the optimal cost-effective method of repeated stimulation (multi-stage fracturing), which is technically complicated by the design of the well. In this paper, we consider the experience of applying the technology of re-stimulation of horizontal wells with multi-stage hydraulic fracturing at the company's fields and the results achieved after repeated hydraulic fracturing (increase in oil production rate, economic efficiency of measures). A proprietary method has been developed, which is currently the most acceptable and cost-effective for re-stimulation of horizontal wells with single-use ball arrangements.