Compound re-fracturing technology for horizontal wells of unconventional oil reservoirs in the Sangtanghu oilfield

The unconventional oil reservoir of the Santanghu oilfield suffers from rapid production decline and low recovery factors of a considerable part of horizontal wells, due to the inferior reservoir physical properties, high heterogeneity, and the small reservoir stimulation scale and low recovered degrees of the primary fracturing treatment. Given this, the compound re-fracturing technology of horizontal wells integrating supplementary perforating based on refined interval division, pre-fracturing energy charging, expansion of reservoir stimulated volumes and promotion of imbibition displacement efficiency and fracture conductivity was developed, and the corresponding treatment parameters were optimized. In 2021–2022, 23 horizontal wells were re-fractured, and the effective treatment rate reached 100%. The average daily oil production of wells was increased from 2.2 t/d before fracturing to 10.5 t/d after fracturing, indicating a daily oil gain of 8.3 t. The average cumulative oil gain of wells has exceeded 1 400 t, and the input-output ratio surpassed 1:1.2, which demonstrates excellent production stimulation performance and high economic revenues. This technology is also valuable for production stimulation of old horizontal wells and improvement of ultimate recovery factors for other unconventional reservoirs.