Study On Methods For Determining The Physical Lower Limit Of Tight Oil

With the rapid development of the petroleum industry and the reduction of remaining recoverable reserves of conventional oil reservoirs,which makes that today's exploration and development had to focus on complex reservoirs with more difficulty,such as tight reservoir.Besides,evaluation and determination of the lower limit of physical properties for effective reservoir of tight oil is one of the key factors for the oil and water zones identification,the precise calculation of remaining reserves,the establishment of development program and the evaluation of economic technology.And the Chang 7 reservoir of the Wucangbao is a typical tight sandstone reservoir.Consequently,it is necessary to determine the lower limit of porosity,permeability and so on.In this paper,I put the Chang 7 tight oil reservoir of the Wucangbao in Ordos Basin as the research object.With the actual situation that it is difficult to determine the lower limit of the physical properties of the reservoir,we comprehensively compared and analyzed the geological data,such as well logging interpretation,oil testing data,reservoir physical property analysis,etc.,and found out the inherent relationship between reservoir physical property and geological,development and other dynamic and static data.According to the principle of statistics and the fluid percolation mechanism of ultra low permeability reservoir,we use 10 kinds of dynamic and static methods to study the lower limit of the physical properties of the reservoir.Finally,the lower limit of the permeability and porosity on the condition of the existing economic and technical are determined.The research has achieved the following results and understandings:(1)Wucangbao oilfield in Ordos Basin is a large sandstone lithologic gas reservoir,the group of Chang 7 tight oil reservoir is continuous distributed with large areas,and the physical property of reservoir is poor.Porosity is mainly distributed between 4%~12%,the permeability is mainly distributed between 0.01mD~1.5mD,generally less than 0.3mD.(2)With the actual situation that the Chang 7 reservoir of Wucangbao oilfield has complex lithology and large variation of physical property,this paper deeply analyzes and studies the “Four Relations”,and establishes the parameter logging interpretation model of the area after identifying the lithology of reservoir.(3)In this paper,we use 6 kinds of static methods,which are empirical statistical method,oil occurrence method logging parameters and intersection diagram method,capacity simulation method,irreducible water saturation method and mercury porosimetry,to determine the lower limit of the target reservoir in the study area,respectively as follows: the lower limit of the porosity(?)is 6.1%;the lower limit of the permeability(K)is 0.040 mD.The reservoir characteristics,formation pressure and other factors had the control function to the physical property of the reservoir,and the dynamic data can objectively and truely reflect the properties of the reservoir.We use the 4 kinds of dynamic method,which are displacement pressure test method and minimum flowing pore throat radius method and oil accumulation method and the test method,to determine the lower limit of the objective reservoir properties,respectively as follows: the lower limit of the porosity(?)is 6.4%;the lower limit of the permeability(K)is 0.042 mD.(4)After the study and comprehensive comparison for lower limit of physical properties for effective reservoir of Chang 7 tight oil layer in study area,we determined that the lower limit of the porosity(?)is 6.2%;the lower limit of the permeability(K)is 0.041 mD.With proved reliable,the standard is the basis for the effective thickness division,reserve calculation and the development plan of the study area at the later stage.