| Ultra-low permeability reservoirs have become an important part of the increase in reserves and production in the Changqing Oilfield.Aiming at the problems of rapid production decline and low recovery factor of horizontal wells after initial fracturing in Block A of Changqing Oilfield,large fluid volume and large displacement were carried out in some wells and good stimulation effect was obtained by close cutting and repeated volume fracturing experiments.However,the re-fracturing location did not consider the effects of the stress field and seepage field before the re-fracturing,which resulted in a huge re-fracturing cost.Therefore,it is of great significance to propose a horizontal well re-fracturing optimization method considering the current stress field and seepage field.Aiming at the problems existing in the optimization technology of re-fracturing in Block A of Changqing Oilfield,based on the formation mechanism of hydraulic fracture network,the mathematical model of stress shadow and its influence on the fracture network,and FracMan fracture modeling and Uncong numerical simulation technology were used.The current actual stress field and seepage field characteristics in Block A of Changqing Oilfield were combined,the complex fracture network of primary fracturing and re-fracturing is described in detail,and the influences of complex fracture network,stress field and reservoir seepage field on the optimization parameters of re-fracturing are deeply studied.Research shows that:(1)In the process of selecting re-fracturing location of horizontal wells in ultra-low permeability reservoirs,two factors are mainly considered,namely fracture network distribution and stress field after primary fracturing and remaining oil distribution and pressure field of producing well group.Among them,through the comparative analysis of stress field and fracture network distribution,the location that is easy to increase reservoir volume by re-fracturing is mainly selected.By analyzing the remaining oil distribution and pressure field variation of the production well group,the location with greater stimulation potential for re-fracturing can be selected.(2)By comprehensively considering the in-situ stress field and seepage field of the current well-controlled reservoir,the following results can be obtained by optimizing the re-fracturing location of A typical well group in Changqing Oilfield:the P50-11 wells were designed to be refractured in 12 stages,and the P52-16,P-5,and P-14 wells were designed to be refractured in10 stages.(3)The optimal cluster spacing of new hydraulic fracture in horizontal wells is mainly affected by the density of natural fractures in well-controlled reservoirs and the angle between natural fractures and hydraulic fractures.Through specific optimization research on different wells of typical A well group in Changqing Oilfield,it can be seen that:the optimal cluster spacing of new hydraulic fractures in well P50-11 with supplementary pressure is 15m,and the optimal cluster spacing for new hydraulic fractures in wells P52-16,P-5 and P-14 is 10m.(4)The SRV increases with the fluid volume and the pump rate,and the The increase of SRV decreases with the increase of fluid volume and pump rate.Considering the purpose of reducing cost and increasing efficiency of re-fracturing optimization research,it is necessary to seek the inflection point for the target horizontal well to achieve the best development effect with the fluid volume and pump rate.A typical well group in Changqing Oilfield adopts 10m~3/min pump rate and 1000m~3/section fluid volume to carry out re-fracturing to obtain the best development effect. |
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