Experimental Research On A New Turnaround Fracturing Fluid

With the rapid development of exploiting extraordinary low permeability oil and gas resources,the existing stimulation technologies can’t meet the demand of oil and gas production.Reservoir stimulation technologies have been developed from conventional hydraulic fracturing to larg-scale volume stimulation.The application of turnaround fracturing in volume fracturing has gradually become the mainstream stimulation technology.In order to realize the original fractures plugged and generate new fractures,temporary plugging agent is usually added in fracturing fluid in the conventional turnaround fracturing.However,the most existing temporary plugging agents have many defects,such as low strength of temporarily plugging,a large quantity of leak-off,difficult plug removal,serious damage to the reservoir.Therefore,these temporary plugging agents can not satisfy the requirements of turnaround fracturing construction.The synthetic method of supramolecular gel is adopted in this thesis to develop a new kind of turnaround fracturing fluid system.The biggest characteristic of the fracturing fluid system is:it makes use of the continuous heating effect of the formation so that it can plug the previous fractures by phase change under temperature stimulation conditions.Then turnaround fracturing can open new fractures.Repeating this operation can make a single hydraulic fracturing construction acquire a number of oil and gas flow channels for the purpose of volume stimulation.In the end of construction,the turnaround fracturing fluid can break gel and remove plug.The concrete research content is as follows:(1)Through the theoretical analysis of mechanism of turnaround fracturing technology,the technical principle of turnaround fracturing,cracking and extension mechanism of factures and the best time of turnaround fracturing,the technological characteristics of turnaround fracturing have been defined.(2)4 kinds of turnaround fracturing fluid systems are developed on the basis of the theory of supramolecular chemistry.The methods of OM,SEM,DSC,FT-IR are used for characterization and study.The effects of different types and concentration of salts and guest molecule on gel systems are analyzed.The turnaround fracturing fluid system which has excellent performance is chosen by testing 4 different turnaround fluid systems.(3)According to the requirements of the fracturing fluid performance,the basis performance experimental evaluation of turnaround fracturing fluid systems is implemented.The results show that the new turnaround fracturing fluid systems have good performance such as:gel forming and breaking performance,thermostability,compatibility,rheological property,the leak-off resistance,low damage and the flowback perfonnance.So it can meet the requirements of turnaround fracturing construction.(4)The temporary plugging and turnaround performance evaluation experiments are conducted.The experimental results show that the turnaround fracturing fluid has good temporary plugging,plug removal and turnaround performance.Its maximum blocking strength is up to 62.3MPa/m.The conclusion can be obtained by the synthesis and performance experimental evaluation of the turnaround fracturing fluid:the turnround fracturing fluid system is a new kind of fracturing fluid which is based on the supramolecular gel.It has the general performance of fracturing fluid and it can also make the fractures plugged and unplugged.Therefore this turnaround fracturing fluid system can satisfy the requirements of turnaround fracturing technology.It has a very important significance in promoting the development of unconventional low permeability reservoir.