Study On Water Injection Development In Zhuang 23 Ultra-Low Permeability Reservoir

The Zhuang23 ultra-low permeability reservoir,characterized by a rapid decline in production and a low degree of reserve recovery,is currently in elastic development phase,and urgently needs injecting water to supplement the formation energy to improve the development efficiency.This paper,through theoretical calculation and numerical simulation,described the study on the waterflood development technical policy of Zhuang 23 reservoir,aiming at providing technical support for its rational development.In this paper,a critical well spacing model is established with consideration of both pressure-sensitive effect and starting pressure gradient.The ultimate well spacing of Zhuang 23is calculated,according to which the current well pattern adjustment scheme is designed the artificial fracture parameter is designed.A three-dimensional geological model of Zhuang 23reservoir has been established,in which the optimization of the waterflood development technical policy and effect prediction have been carried out through numerical simulation.The injection water quality limit was confirmed by the mathematical model of internal granule jamming.The results show that a larger starting pressure gradient and stronger pressure-sensitive effect characteristics are existed in the Zhuang 23 reservoir.Its minimum starting pressure gradient is 0.25 MPa/m,and the stress sensitivity constant?_k=0.0225.The critical well spacing of Zhuang 23,by using theoretical model of critical well spacing,is 173m under the driving pressure differential between 20MPa in the production well and 30MPa in the injection well and with consideration of starting pressure gradient and pressure-sensitive effect.The existing well spacing is able to meet the requirements of critical spacing by fracturing with a half fracture length of 40m-234.8m.At the initial stage of water injection,in accordance of Zhuang 23 well network adjustment plan,a reverse rhombus nine-spot well pattern is formed by injecting 7wells.To form,and in the middle and later,stages 5 wells will be injected to be adjusted to a rectangular five-point well pattern.The technical policy of block waterflood in perforation horizons are 1-7 layers,and the water injection development is carried out with the formation pressure reduced less than 10 MPa.At the preliminary stage,the optimum production rate is1.5%with the employment of reverse rhombus nine-spot well pattern.The optimum production rate of rectangular five-spot well pattern is 1.25%when the water cut reaches about 55%.The optimal adjustment program simulates for 15 years,and the block degree of reserve recovery is14.6%.In order to avoid reservoir blockage during waterflood development,the suspended solids content in designed injection water should be less than 1.0 mg/L,with its diameter less than 0.8?m.