| The oil and gas resources in Tarim Basin are one of the important parts of China’s oil and gas supply,and play an important role in the whole energy history of China.As of April 2018,Tarim Oilfield has built 25 million tons of large oil and gas fields,with cumulative oil and gas production equivalent exceeding 300 million tons,natural gas production accounting for 60%of the total domestic oil and gas production,and oil and gas production equivalent accounting for nearly 70%of the total domestic production of PetroChina,which has made great contributions to national energy security.However,the deep fractured tight sandstone gas reservoir in Tarim Basin has complex geological structure and strong heterogeneity,which has exposed many problems in oil and gas drilling and testing,such as insufficient understanding of reservoir physical properties,insufficient understanding of reservoir damage mechanism caused by micro fractures and fractures,and poor pertinence of reservoir protection technology,It can not meet the current exploration and development of Tarim deep reservoir,so it is urgent to further study the reservoir protection technology of Tarim deep fractured tight sandstone gas reservoir.Taking the deep fractured tight sandstone gas reservoir in Tarim Oilfield as the research object,this paper carried out the research on the damage evaluation method of fractured tight sandstone,formed a relatively complete experimental evaluation method for fractured reservoir damage,carried out the research on the reservoir characteristics and potential damage of the study block,and revealed the damage mechanism and characteristics of fractured tight sandstone reservoir in Tarim Oilfield,A series of reservoir protection technologies for deep fractured tight sandstone gas reservoirs in Tarim Basin are further studied,and a new reservoir protection technology scheme is formed.Field tests are carried out and good application results are obtained.The main research contents and achievements of this paper are as follows:Based on the analysis of reservoir characteristics of deep fractured tight sandstone gas reservoirs in Tarim Oilfield(taking Keshen block as the research target block),the potential damage types of fractured tight sandstone gas reservoirs are analyzed and studied,and the damage characteristics and types of fractured tight sandstone reservoirs are defined.On this basis,a set of experimental methods for damage evaluation of fractured tight sandstone reservoirs are proposed,It is clear that the damage evaluation of fractured tight sandstone reservoir mainly focuses on fracture damage evaluation,and the fracture and base block are evaluated separately.The two evaluation methods complement each other and form a complete set of damage evaluation system for fractured tight sandstone reservoir,which provides the basis for establishing the industry standard suitable for the damage evaluation of fractured tight sandstone reservoir.Based on the analysis of geological characteristics,drilling and completion technology and formation fluid characteristics of deep fractured tight sandstone gas reservoirs in Tarim Basin,combined with the newly established damage evaluation scheme for fractured tight sandstone reservoirs,the formation mechanism of damage in deep fractured tight sandstone gas reservoirs in Tarim Basin is deeply studied,and the damage mechanism of deep fractured tight sandstone gas reservoirs in Tarim Basin is clarified.The results show that the plugging damage of solid particles to reservoir fractures,microfractures and fracture pore interface is the main damage mechanism of the reservoir.At the same time,the reservoir has moderate to strong water/salt sensitivity and stress sensitivity,as well as serious liquid(water or oil)locking damage.The damage of drilling and completion fluid filtrate to the reservoir is serious and can not be ignored.Based on the research results of damage mechanism and geological characteristics of deep fractured tight sandstone gas reservoirs in Tarim Basin,as well as the damage characteristics and particularity of fractured reservoirs,the protection ideas of fractured reservoirs are clarified,and the protection technology construction of fractured sandstone reservoirs is completed.The reservoir protection technology ideas of ensuring no drilling fluid leakage by micro fractures and minimizing drilling fluid leakage by large fractures and vertical fractures are formed,The theory and technology of fractured tight sandstone gas reservoir protection,which is "total acid dissolution+barite chelation plug removal+liquid lock prevention",has been formulated.Based on the theory and technology of "total acid dissolution+barite chelating plug removal+liquid lock prevention" for fractured tight sandstone gas reservoir protection,a new type of liquid lock prevention agent was designed and developed based on the damage mechanism of liquid trap and wetting reversal mechanism,and its performance was evaluated by laboratory experiments.The research shows that when the mass concentration of anti lock agent is more than 1.0 g/L,stable micelles and micelles can be formed on the interface,which can effectively change the wettability of the core surface,and has good salt resistance and temperature resistance.The temperature resistance is above 150℃,which indicates that the new anti lock agent can improve the performance of drilling and completion,and achieve the purpose of anti lock.Focusing on the protection theory and technology of fractured tight sandstone gas reservoir of "total acid dissolution+barite chelating plugging removal+liquid lock prevention",the research on barite chelating plugging removal theory and technology is carried out,and the barite chelating plugging removal theory and technology are formed.The results show that barite chelator can chelate with multivalent metal ions,soften,dissolve,disperse and suspend the mud cake solid phase in the fracture,effectively solve the blockage problem of barite insoluble solid phase,and promote the flow back and reduce the damage.Based on the theory of "total acid solution+barite chelate plug removal+fluid lock prevention",the laboratory experiment of drilling and completion fluid is carried out,and a set of low damage drilling and completion fluid system of "total acid solution+barite chelate plug removal+fluid lock prevention" is formed.The experimental pressure bearing capacity of the system is up to 10MPa.The initial filtration loss of fractures with different widths is very small,and the filtration law is basically the same,The average permeability recovery rate after flowback is more than 60%.It has good reservoir protection performance and can meet the technical requirements of reservoir protection in the process of exploration and development of Tarim deep fractured gas reservoir.Finally,some wells in the study block were selected and field tests were carried out.The test results show that the permeability recovery rate of the test well is greatly improved after using the technology of all acid soluble barite plugging removal and liquid lock prevention,and the leakage prevention performance of the system is also greatly improved.The average loss is 63%lower than that of the well,the acid soluble rate of mud cake is 43.9%higher than that of the well,and the average skin factor is 2.44,The skin factor of comparable wells is generally 3-20 or higher,which belongs to the range of no damage or slight damage,and the reservoir protection efect is very good.This paper systematically expounds the damage mechanism of deep fractured tight sandstone gas reservoirs in Tarim Basin,puts forward a set of new experimental methods and procedures for damage evaluation of fractured tight sandstone reservoirs,puts forward new ideas for fractured tight sandstone reservoir protection and forms a series of reservoir protection technologies suitable for the study area,These results provide a reference for the theory and application of reservoir protection technology for the efficient development of deep fractured tight sandstone gas reservoirs in Tarim Basin. |
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