| The proportion of fracturing in ultra-low permeability reservoirs is greater and greater. Because of the difference of lithologic & physical property and in-situ stresses, low-permeability layers always have thin interlays, whose proportion increases continually these years. Besides, one layer differs from another in physical properties. All these make hydraulic fracturing difficult to construct and give challenge to improving traditional separate layer fracturing methods, as it is hard for them to increase fracture length & width. These traditional methods cannot be applied to thin layer and multiple layers, so this paper focuses on amelioration of separate layer fracturing technology with ball sealer.The essence of new ball sealer fracturing is to change the time & the way of injecting balls at the metaphase of pad. The following are other improvements: In order to control the fracture height and make the ball seat easily, decrease the flow rate while injecting balls. It is also required to try to keep the flow rate as a constant through the whole process of injecting balls to judge if there is a new layer fractured. Before inputting sand, the flow rate should be lifted up to maintain the fluid supply capability for per unit of reservoir height. Meantime, the volume replaced by low viscosity fracturing fluid should be more than the volume of wellbore to make sure that the ball sealers can drop to the bottom hole.This technology avoids the blindness of traditional ball sealer fracturing and the interference of proppant caused by interzonal cross flow. In addition, this technology has important academic and realistic values on enhancing fracturing scale, controlling fracture height, improving proppant profile and gaining favorable effect after fracturing. Field application has proven that this method has a better adaptability, contraposition and maneuverability. Therefore, this method is fit for high efficiency frac stimulation of ultra-low permeability interlays.
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