A Study On The Salting-out Mechanism And Plugging Removal Technology Of High Salinity Reservoirs

The deep gas reservoir of Shizigou has high salinity.The reservoir has complex lithology and complex mineral composition.It has strong fluidity of salt paste and poor longitudinal shielding ability.It is easy to occur salt blocking in the formation and wellbore.It is possible to damage the normal production of gas wells.In this paper,according to the salting out problem of the formation of the Shizigou,we study on the mechanism of the salting out of the formation and its influencing factors,and take measures to the salt-blocking technology which is suitable for the Shizigou reservoir.In order to achieve the salting-out mechanism of high-salt reservoirs and the study of salt-blocking technology,this paper mainly carries out the following work and has achieved the following results:(1)The study on geological characteristics and fluid properties of high-salt reservoirs:The paper analyzes the deep reservoir geological features and salt rock distribution of the Shizigou.The up-dip of the reservoir is blocked by the dense layer of the cream rock layer or the dense limestone layer and mudstone layer.The distribution of salt rock layers and the sandy mudstones make up an inter-bedded layer.The paper analyzes the composition of the reservoir salt.The results show that the main component of the salt scale is sodium chloride.And the paper analyzes the comprehensive reasons of the reservoir salting.The Shizigou formation water's mineralization degree is analyzed,and the formula for calculating the density and viscosity of the brine is fitted.(2)The theoretical study on the dissolution crystallization of sodium chloride:The calculation model of the dissolved crystallization equilibrium constant of sodium chloride is established,and the formula for calculating the solubility of sodium chloride is obtained.The relationship between the solubility of sodium chloride and the pressure and temperature is analyzed.Based on the kinetics,the dissolution kinetic model and crystallization kinetics model of sodium chloride are established to analyze the dynamic process of sodium chloride dissolution and crystallization.Whether sodium chloride precipitated depends on the dissolution rate and crystallization rate of sodium chloride.Through the analysis of the theory of dissolving and crystallization of sodium chloride,the mechanism of salting out of deep reservoir of Shizigou is fully understood.(3)The study on the influence of water saturation on stratigraphic salt formation:In the Shizigou gas reservoir,due to the evaporation and vaporization of the formation water,the water saturation decreases.It can result in salt formation of the reservoir.By deducing the water saturation model,the factors affecting the decline of water saturation are analyzed,and the salt radius of the formation is predicted.The salt formation in the formation occurs within fifteen meters of the well.Based on the established water saturation model,the formulas of salt content,reservoir porosity and permeability are derived,and the effect of water saturation reduction on salt formation is analyzed.The results show that the water saturation decreases and the salt content of the formation increases.Both layer porosity and permeability are reduced.(4)Predicting simulation of stratigraphic salt formation:The salt concentration of deep reservoirs in Shizigou under different conditions is predicted by OLI ScaleChem software.And the effects of pressure,daily gas production,daily water production,temperature and formation water salinity on salt formation are studied.The conclusions are as follows:the daily gas production,temperature and formation water salinity are positively correlated with the salt concentration,and the pressure and daily water production are negatively correlated with the salt concentration.The predicted salt concentration is related to the water saturation model.The influence of salt on reservoir physical properties is analyzed.The results show that the salt has a lower effect on reservoir porosity and permeability.The longer time the well produce,the greater damage the reservoir has.(5)The research on the release of salt plugging technology:In order to solve the problem of salt plugging in the Shizigou reservoir,the solvent content is increased by using water to remove salt,and the supersaturation and high salinity of the formation water are reduced.Through the experimental synthesis of ammonia triacetamide salt inhibitor,increase the solubility of sodium chloride and change the crystal type of sodium chloride.And the high-efficiency salt-inhibiting agent is compounded,and the NTPF-1 high-efficiency slow-release salt suppressant suitable for the geology of the Shizigou reservoir is developed.Combined with water-removal and salt-removal and chemical salt suppression,a comprehensive removal measures which is suitable for the Shizigou reservoir is proposed.