Study and Application of Technology for Preventing and Controlling Mud Losses in Mahu Block

Mud losses were frequently encountered in Mahu block. By carefully study the volume of mud losses, formation porosity, development of formation fractures and leaking pressure profile in this area, the characteristics and mechanisms of mud losses were analyzed. Lost circulation prevention and control slurries for the specific formations were evaluated and optimized, and lost circulation materials were selected using morphology analysis and particle size matching method. It was found in study that the second and the third intervals of the wells drilled in the Mahu block have higher volume of mud losses and high frequency of downhole troubles. The Badaowan formation, Baijiantan formation, Klamay formation and Wuerhe formation penetrated by these two intervals are full of pores and fractures and have low pressure bearing capacity, making them vulnerable to mud losses. Using the lost circulation materials available at the rig site, a new mud loss prevention slurry SDSZ and a mud loss control slurry SDDL were formulated with sized millimeter and micron particles by matching the shape of the particles and the morphology of the loss zones. The mud loss prevention slurry SDSZ was tested on a sand-bed and the depth of filtration of the SDSZ was 50% lower than that of the lost circulation control slurry previously used. The mud loss control slurry SDDL can strengthen the loss zones by increasing their pressure bearing capacity to above 7 MPa. Percent acid solubility of SDDL was at least 60%. In field application, 75% potential mud losses were prevented from occurring, and the success rate of controlling mud losses on the first try was 80%. The mud loss prevention and control slurries developed, as the study has shown, are able to effectively solve the mud loss problem occurred in Mahu block.