Molecular Dynamic Simulation For Shale Gas In Micro-nano-pore And Media Interface

Unconventional resources of oil and gas represented by shale gas have great potential and get a wide attention both at home and abroad.It became the hot spot in the exploration of oil and gas all over the world.The resource of shale gas is very abundant in China,whose reserves is estimated up to several trillion cubic meters that is several times of conventional oil and gas reserves.Therefore,in front of the deficiency of conventional energy of oil and gas day by day,the study about exploration and development of shale gas can provide a new way for China to improve the structure of oil and gas energy and solve the problem of potential threat of current energy.The pore structure of shale reservoirs has a very important influence on the characteristics of reservoir.Micro-nano-pores are major space for shale gas,and the state and density of methane in the mircro-nano-pores of shales have an important influence on the assessment and exploitation of shale gas.According to the actual formation environment,the method of molecular dynamic was used to simulate the adsorption of methane gas by the micro-nano-specific holes.The methane density in different locations of the microstructure was calculated.We used microscopic to convert the density into the effective amount of the active reservoir.In this paper,the typical shale samples of JY1 in Fuling area of Chongqing city were taken as the research object.Using the stratigraphic environment,three adsorption models of different adsorption matrix types(organic matter,brittle minerals,clay minerals)were constructed in the Materials Studio software.And different types of pore structures(rectangular and triangular holes)were constructed in the adsorption models.The molecular dynamic method was used to study the adsorption process of methane in different models with different shapes and different matrix types.The methane density distribution of methane in different matrix types,different hole types and different positions was sorted out by stratified statistical method.Finally,the micro-mechanism of methane adsorption was explored by using Radial Distribution Function.The results show: Under the condition of pressure of 30 MPa and temperature of 328 K,the adsorption of methane in the same model showed a layered phenomenon,and the adsorption capacity of methane in slit and hole was different.The methane density in the pores was substantially greater than the density of free methane in the slit and the methane state in the pores was closer to the liquid.The adsorption density of methane in the rectangular pores and the adsorption density of methane in the triangular pores were slightly different.Under the same conditions,different types of adsorption models,methane adsorption were layered phenomenon,but the specific values of different locations slightly different.The total amount of gas in the organic model was higher than that in the brittle mineral model.Finally,the images of 2415 m deep rock samples of JY1 well were collected by scanning electron microscopy,and the organic matter porosity was identified.According to the graphite adsorption model,the methane adsorption density at different positons was calculated.In the microstructure of shale sample,the contours of the pores were sketched out and the different methane adsorption capacity was given along the boundary area to calculate the gas content of the shale reservoir.The calculated result was close to the actual field analytical values.Therefore,it is instructive to use micro-simulation method to evaluate the macroscopic storage capacity of shale gas.