A new low-cost refracturing method of horizontal well suitable for tight oil reservoirs: A case study on Ma 56 Block in Tuha Oilfield

When stimulated reservoir volume (SRV) of horizontal well is used in the tight oil reservoirs of Ma 56 Block in Tuha Oilfield, the high-yield period is short and the primary recovery factor is low, so it is necessary to increase the production rate by means of refracturing. However, the conventional fracturing can hardly satisfy the horizontal well stimulation requirement at low oil price. therefore, a new low-cost refracturing method of horizontal well was explored. Firstly, the previous production characteristics of Ma 56 Block were analyzed. Then, in order to combine EOR with SRV, 4 basic tests were conducted, i.e., core wettability test, long core test, numerical simulation and field water injection test. It is verified that the combination of high-rate water injection and SRV is beneficial to the production recovery of horizontal wells. Finally, a new refracturing method was developed. In this method, water is injected before SRV at high rate to store the energy (injection rate is 2 times of production rate), then slick-water+small-size proppant refracturing is carried out in the whole course at the rate higher than that during the initial fracturing, and finally well soaking is performed for 5-15 d. Its field fracturing test is successful. After 6 times' fracturing, the average daily oil production is 18.1 t/d, which is 77.4% of the oil production rate after the initial fracturing, and its cost is RMB1.4 million/well time lower than that of the initial fracturing. This method combines the commingled water injection with the refracturing, and it provides a new way for horizontal well refracturing of tight oil reservoirs.