Multi-stage fracturing stimulations improve well performance in tight oil reservoirs of the changqing oilfield

The oil reservoirs in the Changqing Oilfield consist of stacked sand/shale deposits, and the majority of the target zones have a permeability of 0.05-0.3mD. All oil wells completed in tight reservoirs from the Changqing Oilfield require fracture stimulation to achieve commercial production and to improve well productivity. Fracture stimulation is also very common for water injection wells to enhance injectivity. Multiple payzones in the region were either stimulated with standalone treatments that were isolated and pumped separately or with single-stage treatments to simultaneously treat several intervals using a kind of limited-entry technique. However, with the continuing development in these fields, larger pay intervals (gross pay thickness up to 75 meters) with poorer reservoir quality were encountered. Post-fracture production results indicated that the above stimulation techniques were not always effective in these tight reservoirs. As a result, a new staging technique was evolved and employed to stimulate these tighter reservoirs with better economic effectiveness. With this technique, two or three pay intervals were first perforated and dual-stage fracture treatments were then performed: one stage at a time without using any mechanical isolation. The idea was two-fold: a) using the stress increase around the fracture created by the first injection to divert the subsequent treatment to un-stimulated interval(s), and b) using the proppant banks created from the first propped treatment to minimize the proppant settling to the bottom portion of the fracture created by the second propped treatment. Three-month average post-treatment production data indicated that the dual-stage treatments outperformed conventional single-stage treatments in some reservoir environments. Candidate selection was a key to the success of this technique, and reservoir conditions that favor these types of treatments are as follows: multiple pays, lower permeability, lower net pressure, and less stress contrast between different payzones. Radioactive tracer logging and microseismic fracture mapping were conducted to evaluate fracture height growth. This paper presents a case history of fracture performance evaluations. Reservoir data, fracture modeling and post-fracture production data were compiled and employed to demonstrate the benefits of this fracture treatment technique in some tight oil reservoirs. ©2008,Internation Petroleum Tecnology Conference