RESERVOIR DAMAGE MECHANISM OF DRILLING MUD IN TIGHT SANDSTONE GAS RESERVOIRS IN SHENFU BLOCK

In recent years, more and more attention has been paid to the exploration and development of unconventional oil and gas such as coalbed methane, shale gas, and tight gas. At present, CNOOC has carried out a pilot test of tight gas exploration and development in the Shenfu block of the Ordos Basin. Tight sandstone gas reservoirs have low porosity and permeability, and is easy to be polluted during drilling. The drilling and completion fluid is an important technical carrier for implementing reservoir protection measures during the drilling process. Therefore, it is necessary to systematically study the damage mechanism of drilling fluid to reservoirs according to the characteristics of tight gas reservoirs in tight gas fields in the Shenfu block. The research results show that the mud has a certain degree of damage to the core, and the permeability damage ratio is 2.39.1, which belongs to mild and serious damage. The damage of the mud to the core is mainly reflected in the first 2 hours. The factors that damage the permeability of the reservoir are: first, the solid particles of the mud directly block the seepage channel. Second, due to the low permeability of the rock, after the organic components in the mud enter the voids, water lock and adsorption effects occur. In general, organic components have less damage to core permeability, and the longer the soaking time, the greater the damage. Third, drilling mud can change the salinity and alkalinity of the reservoir fluid, causing a certain degree of reservoir sensitivity damage.