Productivity Evaluation of Refracturing to a Poorly/Damaged Fractured Well in a Tight Reservoir

As an important stimulation technology, refracturing is commonly used to enhance oil or gas recovery in tight reservoirs, particularly for poorly/damaged fractured wells in these reservoirs. However, the stimulation effect of refracturing is not clear at present. Accurate evaluation of the effect of refracturing treatment on the productivity of a poorly/damaged fractured well is of great significance to the rapid and efficient development of tight reservoirs. In this study, two semi-analytical models, including an initially fractured well model and a refractured well model, were established to calculate their productivity indices, respectively, for quantitative productivity evaluation. Productivity index ratio, a newly defined parameter reflecting the characteristics of both productivity indices, was calculated to evaluate the refracturing stimulation effect. The comparisons with two classic cases indicated our solutions were exactly consistent with the results in the previous literature and verified the reliability and accuracy of our solutions. Results show that compared with initially fractured well, the productivity of refractured well first rises rapidly and then slows down as principal/reoriented fracture angle or rotation angle increases, but an inverse relationship may occur at low initial fracture conductivity. Meanwhile, the productivity index ratio curves under the same initial fracture conductivity converge into a bunch of curves, first increasing and then slowing down as reorientation fracture conductivity enhances. Overall, refracturing treatment is more effective for fractured wells when initial fracture conductivity becomes lower. Reoriented/principal fracture length ratio has a weak negative correlation with the productivity index ratio, but reorientation fracture number shows a stronger influence on the stimulation than the other factors. Principal/reoriented fracture angle, fracture length ratio, reorientation fracture number and fracture conductivity should be optimized before refracturing to achieve the optimal productivity. Additionally, in a rectangular reservoir, the central refractured well obtains larger productivity than the eccentric refractured well, and hydraulic fractures deploying along the reservoir extension can slightly increase well productivity.