Studies Of Drilling And Completion Fluids In Low Permeability Sandstone Reservoir

The oil and gas production from low permeability formation received more and more emphasis in China. The specific characteristics of low permeability reservoir, such as narrow pore throat, strong anisotropy, high content of clay and rich with micro- fractures, make the reservoir more prone to be damaged. So it need the newly developing low-damage drilling and completion fluid systems and formation damage control measures to increase the production of individual well. This thesis mainly studied the bottleneck problems restricting the exploitation and development of low permeability sandstone oil and gas field. New evaluation technologies of formation damage of low permeability sandstone formation and reservoir protecting drilling and completion fluids have been developed, and the comprehensive technologies have been tested.The Formation Damage Evaluation Apparatus has been developed, through which the core flooding test can be done for permeability as low as 0.1 mD. The capillary imbition and liquid retention methods have developed to found the low permeability evaluation methods.The formation damage mechanisms has been studied in details. Water trapping is the main damage factor in low permeability and the controlling factors to reducing the water trapping in compact sandstone gas reservoir.Using loading core micro imaging analysis system, the integrated measures coupling with core observation and thin section analysis, core fracturing simulation stress and loading core micro imaging analysis has been established, which can be used to study the opening and closure of fractures under primary crustal stress, and the formation damage induced by stress can be determined in quantity.Newly developed anti- water blocking clay free drilling fluid and bio-completion has been used in many tiny reservoirs of Erdos Block Gas Field and Shengli Oilfield. The formation damage mechanisms has been studied and the reservoir protection measures has been established. Through reservoir protecting technology application in 15 wells, better results have been achieved. The history of no production without fracturing was ended.The newly developing anti-oil high efficiency foam drilling fluid has been successfully used in three wells DP 14, DP19 and DP22, but during the drilling, there are some matching technologies should be further investigated.The self blocking-removing drilling fluid system with proprietary intellectual property rights has been developed, which exhibits anti-high temperature, strong anti-calcium ion, strong anti-cuttings, benign reservoir protecting, and so on. The mean recovery permeability can be higher than 90.0%. The mudcake is more hydrophobic, which can resist the water passing and liberate the oil phase. When soaking in the oil phase, the mudcake can be removing completely, realizing the formation damage self removing.