The Influences Of Bedding Plane And Crack On Aqueous Imbibition Characteristics Of Shale Gas Reservoirs

Spontaneous imbibition and absorption of fracturing fluid by shale reservoirs is a key factor affecting oil and gas production in the process of hydraulic fracturing of shale gas reservoirs.Shale reservoirs have rich development bedding structures and microcracks due to their formation characteristics.However,the influences of these complex cracks structural systems to the fracturing fluid absorption still lack a certain understanding.At present,there is a lack of research and understanding on the spontaneous imbibition of fracturing fluid in reservoirs,as well as the understanding of the microscopic imbibition law of stratified fracture structure and microscopic pore cracks structure.The role and influence of fluidic migration and bedding fractures in the process of imbibition have not been further analyzed and understood.This paper starts from the engineering background of "Shut-in" and "backflow" of shale reservoir fracturing process.The traditional laboratory spontaneous imbibition experiment method and core treatment were used to seek breakthroughs.The process of this paper firstly uses scanning electron microscopy to observe the micro-bedding planes and cracks structure of shale reservoirs,and uses image processing technology to calculate the corresponding face rate,and then calculates the fractal dimension that reflects its complexity according to the shape characteristics of the pores.Spontaneous imbibition experiments were carried out with different fractal dimension and different bedding cores,and real-time monitoring of nuclear magnetic resonance was performed simultaneously.After that,the effects of micro-cracks and pores on imbibition were studied by combining NMR curves and spontaneous imbibition curves.In general,the following research results have been obtained:(1)A set of analytical and experimental methods for matrix pores and micro-cracks in shale reservoirs has been initially formed and the relationship between the structural differences of bedding planes and the underlying physical properties of reservoirs can be quantitatively analyzed through digital technology.It is found that there is a positive correlation between fractal dimension and organic carbon content.(2)A set of experimental scheme and evaluation parameters that can control the influence of unconventional shale reservoir bedding planes and cracks on spontaneous imbibition are initially formed.The regularity of the imbibition rate and the quantity of imbibition of different bedding planes and cracks to the spontaneous experiment is analyzed.The spontaneous imbibition experiment shows that the rate and amount of imbibition in the direction of parallel bedding are greatly increased which implies that the bedding planes may be the main cause of this phenomenon.(3)A set of experimental schemes for simulating microscopic fluid migration in the process of reservoir “Shut-in” and “flowback” processes were initially formed.From the perspective of cracks with different structures,the internal imbibition law was analyzed.And the experimental also defines its mode of action and its characteristics in macro and micro scale.(4)The influence and effect of bedding planes and microcracks on actual engineering development are initially analyzed.