Calculation Of Shale Gas Content And Sensitivity Analysis

Shale gas is a typical unconventional oil and gas reservoir,and its storage conditions,reservoir formation mechanism,and reservoir characteristics are quite different from those of conventional oil and gas reservoirs.Therefore,the assessment of conventional oil and gas reservoirs does not apply in shale gas.Based on the typical characteristics of shale gas,the calculation of shale gas content can be explored,which can provide the basis for the evaluation and calculation of shale gas reserves in China.Based on the previous research,main factors and calculation methods of shale gas content are studied in this paper.The main contents and results are as follows:(1)The factors that affect the shale gas content are the total organic carbon content(TOC),kerogen maturity(Ro value),development degree of fracture,pore structure,clay mineral and brittle mineral content,temperature,pressure and humidity.Among them,the TOC content is the core element of shale adsorption,and positively correlated with the adsorption gas.Resistivity and porosity logging curve overlap method,radioactive uranium element and total organic carbon regression method are commonly used in the calculation of organic carbon content;Ro value represents the degree of thermal evolution of the shale,basically there exists a positively correlation between Ro value and shale gas content within a certain range,usually using vitrinite reflectance or specular reflectance to measure Ro value;pores determine the specific surface area of shale,according to the shale rock physical model,a variety of logging parameters equations are established to calculate porosity;when the water content is more than 4%,the greater the humidity of the shale,the poorer the reservoir capacity,the Simandoux equation is used to calculate the water saturation of the shale;the temperature inhibit adsorption capacity,when the pressure is constant,the higher the temperature,the worse the adsorption capacity,the stronger the desorption capacity;the pressure promote the adsorption capacity,when the temperature is constant,the greater the pressure,the stronger the adsorption capacity.(2)Using the indirect method,the main factors influencing the adsorption capacity of shale gas are depth(H),TOC,Ro,and H reacts the mutual effect of T and P.Considering the three factors,the variability function spherical model is used to simulate the trend of TOC,Ro value and adsorption gas volume under the formation condition.Orthogonal analysis was used to quantitatively study the effect and sensitivity of different influencing factors.Under the actual situation,with the increase of H,T,P increase at the same time,and there is a depth turning point between V and H,and above the depth turning point,pressure is more sensitive than temperature,while below this point,temperature is more sensitive than pressure.The calculation model can assess any shale gas resource under different H,TOC,Ro;and the analysis method can also provide the basis for parameter optimization in shale gas reservoir.(3)Based on the general method of free gas calculation,since the pore diameter and the methane gas molecular diameter are at the same order of magnitude,the proportion of the adsorbed phase volume in the total pore volume cannot be neglected,so the adsorption phase volume should be subtracted from the total pore volume to correct free gas.