Turned To Repeated Fracturing Technology Research And Application

Having investigated all-sidedly the domestic and international literatures about hydraulically re-fracturing which includs stress reorientation mechanics, reservoir simulation, fracturing design, and treatment technology. This paper absorbed the recent re-stimulation research accomplishment. Then, technique of choosing the candidates and analysizing mechanics interior of inducing new fracture were systemically studied. The major work of this paper is:(1) The classical parameter (statistics) estimation method, experience nonlinear model and statistics learning theory had analysized for choosing a suitable goal interval/layer. According to the bottle-neck problem, such as " data limited "," model and parameter forbid " and " a lot of problem mechanisms are not settled ", making-decision model about genetic algorithm-artificial nerve network and support vector machine had put forward, and computer software were be developed. The practice from the field proved that they have better adaptability for hydraulically re-stimulation treatment.(2) At first, initial in-situ stress field have been studied. Then, induced stresses by propped fracture have been studied according to elastic mechanics and change of pore-elastic stress by theory of coupled fluid and rock. Thus, the current stress field in the layer was determined by principle of stress add. The stress change difference in direction of principal stress is key to new fracture re-orientation caused by stress reorientation.(3) By maximum tension theory and maximum strain energy density theory in fracture mechanics, created and propagation direction of new artificial fracture are analysized. For tensile (I) type crack, fracture will extend and will not arise minute along crack surface branch. For inner shear (II) type crack, created-fracture angle is -70.5° according to maximum tension theory, but the angle has nothing to do with material nature. On the other hand, according to maximum strain energy density theory, the created-fracture angle has something to do with material property and fracture angle, the re-stimulation crack can have arbitrary angle.(4) A new type of plugging agent has developed to be used to plugging existed hydraulic fracture so the refracture direction be changed. It has breakthrough strength as high as 65 MPa and good rheology characteristic. It can meet the requirements of re-fracturing treatment.(5) It was proved from the oilfield that alter-orientation refracturing technology was reflexable and reliable. It created a new way for restimulation.