Foam Cement Engineering and Implementation for Cement Sheath Integrity at High Temperature and High Pressure

摘要

Cementing high-pressure, high-temperature (HPHT) wells poses various challenges not seen at normal well conditions. For instance, the following objectives are critical for HPHT wells: ? Prevent losses during drilling fluid circulation and cement slurry placement. ? Displace the drilling fluid and place the cement slurry effectively. ? Prevent free-water or gas-channel development. ? Reduce slurry fluid loss. ? Provide support for the production packers. ? Decrease compression loads on casing connectors. ? Prevent damage to cement sheath. ? Prevent annular gas pressure over the life of the well. The industry is recognizing the interaction between these factors to determine the optimal cement job design for accomplishing these objectives. This paper presents and discusses the engineering analysis to determine the optimum foamed cement sheath properties for integrity during the life of the well at HPHT conditions. Also, this paper compares foamed cement to nonfoamed slurries in achieving these objectives. Other important issues discussed are the performance of nitrogen at HPHT conditions and the rheological properties of the foams. Key issues addressed are the state and solubility of nitrogen under downhole conditions and the integrity of the cement sheath during the life of the well. Thermodynamic solution theory and experimental studies are applied to the former, and finite element analysis is applied to the later. Case examples are presented discussing foamed and conventional operations at near HPHT conditions for someNorwegian, North Sea wells. Cement properties are contrasted for the different foamed and conventional cement slurry properties with respect to: ? Achieving the HPHT objectives, such as placement efficiency and sheath properties ? Prejob design to obtain the objectives ? Job planning and procedures ? Job execution ? Logging of foamed cement ? Post-job evaluation of the cement systems