Study On Change Law Of Reservoir Fracture In Chaheji Oilfield

The water-injection method has been used to explore the Chaheji oilfield in North China for many years,where microfractures and artificial fractures have been seen in the reservoir.The formation of these fractures has caused water well turbulence and unbalanced water injection during development process,impacting the development of oil fields and the distribution of residual oil.It is of great significance to clarify the variation characteristics of fractures in order to improve the development of water injection in oil fields.In this paper,the reservoir of Chaheji oilfield is taken as the research object,and the characteristics of the reservoir are analyzed.The porosity,permeability and stress sensitivity characteristics of the reservoir core are tested.The permeability-NMR integrated equipment,the fracture stress sensitivity test and Rock Deformation law experiments are used to analyze the fracture permeability,fracture opening and the law of fracture changes.This paper researches the following research results:1.The pore permeability and triaxial stress tests were performed on the reservoir core of the target block,and the target reservoir porosity and permeability were measured.The porosity was in the range of 11%-15% and the permeability was in the range of 3.4-63 m D.The target block is a middle-porous and low-permeability reservoirs.Rock mechanical parameters under different confining pressures are obtained.The data shows that as the confining pressure increases,the Young's modulus of the rock also increases.2.Using the permeability-NMR integrated equipment,the natural core of the mine was tested for the wide band of natural microfractures.Tests found that under different confining pressures,the NMR T2 spectrum would change,and the width of the cracks under different confining pressures was obtained.3.Conducted empirical studies on the variation characteristics of core and artificial core using NMR.Experimental results showed the following: The conductivity of fracture exhibits apparent staging characteristics: specifically,following the open-up of a fracture its conductivity first shows slight increase then the pace of increase slows down.In addition,artificial fracture has a clearer characteristic as compared to fracture: Its conductivity initially increases significantly and then keep increasing gradually.4.Using the equivalent flow method,the method of inversion of fracture permeability using production data was deduced,and the relationship between fracture permeability and total flow resistance was obtained.As long as the total seepage resistance is obtained from the production data,the fracture permeability can be calculated.At the same time,the permeability calculation model under the presence of proppant is theoretically established,and the variation law of the fracture conductivity under high closing pressure is obtained.The influencing factors of fracture conductivity is analyzed.The research results of this paper provide basic data for the development and decision-making of Chaheji oilfield in North China.