Effects of interactions in natural gas/water/rock system on hydrocarbon migration and accumulation.

The study of natural gas accumulation process in tight formation has become the focus of the petroleum industry. One of the priorities is the effects of interactions in natural gas/water/rock system on hydrocarbon migration and accumulation process. On the macroscopic scale, we investigate the interactions in natural gas/water/rock system by formation fluorescence test and production data analysis. One the microscopic scale, the mechanisms are revealed by mathematical analysis and experimental methods considering the variation of geological temperature and pressure. The effects of interactions in natural gas/water/rock system are also simulated by numerical simulation. The results are visualized and quantified. A novel semi-analytical method based on a physical experiment is proposed to calculate the temperature- and pressure-dependent contact angle and interface tension which reflect the interactions in the natural gas-water-rock system. This semi-analytical is embedded in the numerical simulation during the simulation of the natural gas charging process. The results indicate that with the increase of geological temperature and pressure, the contact angle will increase and the interface tension between natural gas and water will decrease. The capillary resistance in the formation will be reduced. Since the decrease of capillary resistance, the natural gas can be charged into smaller pores, so that the actual charging threshold is lower than the one originally obtained under present reservoir conditions. After considering the temperature and pressure during the accumulation process, some sand bodies that were thought not to be charged may have natural gas accumulate.