Damage of Fracture Face Skin in Massive Hydraulic Fracture Stimulation

Multi-stage fractured horizontal wells can create fracture networks and increase the contact area between fracture and matrix to enhance well productivity and EOR. It has become a tendency to pump large volumes of fluids and proppants with higher and higher slurry rate during hydraulic stimulation. While field production has presented that not all productivities have positively relation with the increase of stimulation scales. Some small-scale fractured wells even perform better than the massive treatment ones.To investigate this phenomenon, a new evaluation experiment studied by CT scanning and rock mechanics testified the existence of the fracture surface damage, and some key factors were revealed. Moreover, we established a new mathematical model of fracture surface skin with segment characteristics using fluid coupling method based on the classical model of PKN and KGD. Comparison of the Cinco-Ley model and new model revealed that influence of the fracture surface damage skin on productivity was only 5% using Cinco-Ley model, while the influence was 50% using our new model.The results indicated that for a specific low permeability reservoir, if high net pressure can't create complex fracture, it would bring formation damage in the near well. We put forward a method for low damage treatment as following: 1)utilize the newly developed fracturing fluids such as slick water, low concentration densifier, linear gel (not cross linked), low molecular weight fluid, etc.; 2)Optimize minimum viscosity of fracturing fluid, then optimizing the corresponding pumping rate; 3)Optimize combination of fluid and proppant type and size according new mathematical model; 4) Try acid-fracturing during pad stages so as to minimize formation damage and fracture damage to obtain an optimized propped profile.The technology has been put in to filed application in 45 wells, the performance of post-fracturing is very remarkable with the daily oil rate being 14m3/d increased more than 32.2% that of the past well stimulation, and it has a great significance in the near future.