Effect on Water-Resistant Cement Slurries by Materials Non-Dispersible in Water

In the Chuanyu area, the shale gas producing Jialingjiang Formation is developed with plenty of fractures and formation water. This leads to a mud loss problem which greatly prolongs the drilling time and hinders the safe and efficient development of the shale gas. Cement slurries non-dispersible in water have been studied to deal with the mud loss problem encountered in the shale gas drilling. By evaluating the water non-dispersibility of five polysaccharide polymers and organic polymers, key materials and their quantity ratio are selected, and a low-density cement slurry non-dispersible in water is formulated for cementing water-bearing loss zones. In well cementing with this cement slurry, pressure balance loss control technique was used, and the cement slurry, after being displaced into the well, is not displaced and washed away by the formation water from the loss zones, hence realizing effective sealing of the loss zones and paving the way for subsequent operations. This low-density water non-dispersible cement slurry has been successfully used in cementing the well Z203H6-X drilled in the Chuanyu area, the equivalent circulating density (ECD) of the formation into which mud has been lost is increased from 0.99 g/cm³ to 1.21 g/cm³. In subsequent operations lost circulation slurries were used to enhance the compressive strength of the formation, and the ECD of the formation was further increased to 1.81 g/cm³. This cement slurry has provided a technical means to solve the lost circulation problem encountered in drilling the fractured water-bearing formations in shale gas drilling in the Chuanyu area.