Scientific Approach to Planning and Implementation of Blind Refracturing in Horizontal Wells with MSF Completion in Low-Permeability Reservoirs

Abstract

One of the fundamental methods of developing low-permeability reservoirs is the use of multi-stage hydraulic fracturing in horizontal wells. Decreasing wells productivity requires geological and technical measures, where one of the methods is "blind" refracturing. Often, only one "blind" hydraulic fracturing is carried out for all ports of multistage hydraulic fracturing, the possibility of carrying out two or more stages of "blind" hydraulic fracturing is considered in this article. The purpose of the article is to increase the productivity of horizontal wells with multi-stage hydraulic fracturing by the "blind" refracturing method. A one-stage and two-stage approach was implemented when planning and performing "blind" hydraulic fracturing with analysis of treatment pressures, indicating a possibility for reorientation of the fracture during the second stage in a horizontal wellbore. Based on the experience of the "blind" hydraulic fracturing performed at the Kondinskoye field, "NK "Kondaneft" JSC carried out pilot work on "blind" refracturing at four horizontal wells of the Zapadno -Erginskoye field. A geomechanical model was used, built based on well logging and core studies carried out at "RN-BashNIPIneft" LLC. The total mass of the planned proppant per well was 280-290 tons, while this tonnage was pumped in one or more stages. A one-stage "blind" refracturing approach was successfully performed in one well, two-stage hydraulic fracturing was implemented in three wells, where in one of the wells, after two stages to open ports, initial hydraulic fracturing was also carried out to the last, previously non-activated port. In the case of two-stage hydraulic fracturing, the first stage purpose was to saturate the reservoir-fracture system with the injection of a "sand plug" with a high concentration of proppant at the end of the job to isolate the initial injectivity interval, determined based on the interpretation of well logging data and analysis of the wellhead treatment pressure. The second stage purpose was the initiation and possible reorientation of the fracture in a new interval, confirmed by an increase in surface pressure during hydraulic fracturing and instantaneous shut-in pressure. This article summarizes the results and lessons learned from the pilot works carried out using the geomechanical model and well productivity assessment before and after "blind" fracturing. The analysis of surface pressure based on production data indicating fracture reorientation is presented. The recommendations and accumulated experience presented in this work should increase the effectiveness of repeated "blind" refracturing in horizontal wells with multi-stage hydraulic fracturing.