Cementing Wells Penetrating Clastic Rocks with Self-healing Cement in Block Tazhong

The clastic formations in the Block Tazhong have complex structures, poor lithological characters and toughness, and high brittleness. During drilling operation, wells penetrating the clastic formation have experienced borehole collapse and sloughing, and borehole of irregular sizes was formed. Cementing of the production casing string has long been facing with diffculties such as low formation pressure and mud losses in the Permian system, coexistence of oil and water in the same zone, interbedding of sandstone and shale, thin sandstones and hence multiple pay zones, short distance between a pay zone and a water zone, and inter-channeling of oil and water, etc. Based on the study on the mechanism of gas-channeling in cement slurry, a leading slurry with density of 1.35 g/cm³, and a tail slurry with density of 1.88 g/cm³ were formulated with several additives, such as silica powder, lightweight material BCE-610S, medium temperature retarder BXR-200L, drag reducer BCD-210L, self-healing agent BCY-200S and anti-channeling flter loss reducer BCG-200L. This cement slurry had good stability, mobility, zero free water, low fltration rate (flter loss<50 mL), elastic modulus near 7 GPa, high compressive strength, and ability of anti-channeling. By optimizing the composition of the cement slurry column in hole, pressure balancing during well cementing was realized. Using well cementing software, the displacing effciency was improved. As a set of self-healing cementing technology, it has been used in 4 wells in Tazhong, all cementing jobs successful, especially the main pay zones which were cemented with excellent job quality, effectively solved the diffculties in well cementing in clastic rock formations.