Study On Void Volume Of Cavity Bottom Deposit In Salt Cavern Gas Storage

As gas storage, salt caverns has important practical and strategic significance, but the salt rock of our country has a characteristic of layered distribution, argillaceous interlayer and higher levels of insoluble impurities, etc. At the end of the dissolving cavern, there will be thicker cavity accumulation of insoluble material, and occupying a large storage capacity, so it is necessary to study and evaluate the void volume of accumulation, master the volume loss of the cavity, and thereby providing a theoretical basis for the crafts of gas injection and drainage.This paper will analyze composition and distribution of the insoluble material after the soluble experiment, and based on experiments and the simulation of the deposits porosity testing to get the accumulation porosity of every layers, then evaluate and revise the existing accumulation model, getting the calculated method of void volume accumulation according to the interpretation results of the site log, then predict the volume expansion of the crafts of gas injection and drainage. The following understanding:(1) According to the soluble experiment of the salt rock sample, measured the particle size and size distribution of deposits, the results have shown that the particle size distribution in line with the fractal distribution. The study found the sample solubility has a linear relationship with the fractal dimension D, so it can use the fractal dimension of the particle size to describe the characteristics of different insoluble matter.(2) Measured the particle porosity of different size distribution by gas expansion method, the results show that the sand porosity of different particle size distribution is smaller than the single particle; the experiments of brine on the accumulation porosity show that the brine increases the accumulate porosity of smaller particles, but little impact on the porosity of larger particles. Experiments of gas injection and drainage shows the accumulate porosity is less than the anhydrous accumulation body, indicating the presence of bound water accumulation.(3) Based on Discrete Element Method to simulate the accumulation of the deposits particle, the simulation porosity of the overall deposit is36.41%; Simulating the porosity of different fractal dimension of each group deposits, studies show that the fractal dimensions has a linear relationship with the simulation porosity, as the fractal dimension increases, the simulation porosity decreases.(4) Simulating the accumulation of the experimental sample particle of different size distribution, simulation and experimental results show that the presence of contrast differences in porosity, because the theory can’t simulate irregularly shaped particles. Thus obtained form factor of the experimental samples is1.184, the corrected actual porosity value of the overall rock samples deposit is43.11%.(5) Based on the experiments and simulations to evaluate the various accumulation model, studies have shown that the fractal model can accurately characterize the sample accumulation porosity according to the solubility of the sample; for the compressibility model (CPM), fixed the system compaction index K is4.03according to the data of measured small particles, then calculated simulation porosity of the particles, and compared with the simulation results, showing that CPM model calculations is also accurate.(6) Based on fractal model and CPM model obtained the field applications calculation method of the accumulation porosity, combined with logging data to calculate the accumulation porosity, the calculation result of CPM method is slightly smaller than the fractal method (fractal is45.76%, CPM is48.23%), the porosity of field test is42.66%and then predict the volume expansion of the crafts of gas injection and drainage according to the porosity.