A Research On Related Technologies Of Formation Damage Control For Deep Gas Well In Xujiaweizi

By analyzing the general geographical overviews, meteorology, hydrology, and the background and basic characters of regional structure, formation generalization, the conditions of source kitchen, reservoir and cap rock, fluid characters and types of gas reservoir etc, we conduct a deep research on the damage mechanism of gas reservoir and measures of reservoir formation damage control, meanwhile develop some research on the following aspects such as water sensitivity, salt sensitivity , flow rate sensitivity, acid sensitivity, alkali sensitivity, pressure sensitivity of the gas reservoir, the problem about damage of inorganic and organic scale, solid invasion, water lock damage caused by drilling fluid filtrate are also discussed. In the end ,we come to conclusion that the reservoir damage in deep gas well of Xujiaweizi is mainly caused by water sensitivity, and then flow rate sensitivity, the pressure sensitivity and alkali sensitivity relatively have slight influence on gas reservoir, and there is no damage because of acid sensitivity. If the reservoir formation has enough energy to displace the water lock section, water lock will cause slight damages, otherwise the damage will be serious.In this paper, the method was established for formation damage control of gas reservoir, the method have fully considered several factors which can influence the reservoir. During drilling, the main damage to the gas reservoir is solid block caused by solids in drilling fluid or completion fluid which invade into crack or caused by the lost circulation. Filtrate of drilling fluid can cause water sensitivity, water lock and alkali sensitivity damage, filtrate which contains high quantity positive ions can cause inorganic scale damage. According to the field requirement, we have developed drilling fluid system with high temperature resistance and ultra low fluid loss and effective protection program. The KWB-1 can significantly enhance high temperature resistance of other fluid loss control additives, it has character of synergistic action, good compatibility, and good gel maintenance capability, simple to operate, easy to maintain.The porosity of gas reservoir in the main faults belt in Xujiaweizi is 2%-10%, its permeability is about 0.04-2.574 md, and it is easy to be damaged during drilling process. To control reservoir damage in this area, reduce the damage caused by drilling process, we should prevent solids from invading micro fissures and the damage caused by fluid loss, reduce the damage caused by filtrate in low permeable formation, use the suitable drilling fluid density, and shorten the time of formation exposed to drilling fluid.