Application of Combined CO2 Pre-Injection and Temporary Plugging Diversion Fracturing Technology in Mature Tight Oil Fields: A Case Study of the MZ Block

The Block MZ features tight reservoir physical properties and poor interlayer connectivity, making conventional injection-production patterns ineffective for formation energy supplementation. Although high initial production can be achieved after fracturing, stable production is difficult to maintain, resulting in a low ultimate recovery factor. To improve reserve utilization, two rounds of well pattern infilling and well adjustment have been implemented in the block, reducing the well spacing from the original 400 m to less than 50 m. The reservoir development has experienced three stages: depletion development, water huff and puff, and water flooding combined with fracturing. Nevertheless, the current recovery degree remains only approximately 7.0%. No obvious high-pressure main fractures are identified during the drilling, logging, and fracturing operations of infill wells, indicating that a large amount of remaining oil within the well spacing of 50–100 m has not been effectively produced. To further enhance the recovery factor and remaining oil producing degree of the mature tight oil reservoir in Block MZ, a novel combined fracturing technology dominated by pre-CO2 injection, temporary plugging and diversion, and volume fracturing is innovatively proposed with the well group taken as the overall production enhancement unit. This technology effectively improves fracture complexity and expands the CO2 sweep volume. Field application results demonstrate that the proposed technology can not only boost the production of a single well but also realize collaborative production enhancement of the entire well group. Compared with the conventional volume fracturing adopted in the early stage, the effective influencing radius of the well group is expanded from 50–150 m to 200–350 m, and the number of affected wells increases from 4 to 6–7. The average daily oil increment per well in the initial 90 days rises from 2.4 t/d to 8.1 t/d, and the average cumulative oil increment per well during the natural flow stage increases significantly from 67 t to 692 t. The remarkable production enhancement effect provides a novel technical approach for EOR (enhanced oil recovery) in mature tight oil blocks.