Kris Ravi

Design approach to sealant selection for the life of the well

Recent experience in the field has demonstrated that the mechanical properties of the annular sealant are a critical factor in the success of a well. A demanding operational regime of the well such as High Pressure/High Temperature (HP/HT) and well interventions, e.g. pressure testing stimulation, put a strong emphasis on the mechanical design of a candidate sealant

Experimental and Numerical Study of Drilling Fluid Removal from a Horizontal Wellbore

After a well has been drilled, the drilling fluid should be removed and replaced with either cement and/or completion fluids. For effective zonal isolation and optimum hydrocarbon production during the life of the well, the entire drilling fluid should be removed from the annulus Cement and completion fluids are sensitive to drilling fluid contamination, and even a thin layer of oil-based drilling fluid could prevent the cement from bonding to the formation and the casing In addition, for optimum hydrocarbon production, the cement sheath must be able to withstand the stresses throughout the life of the well. 1 Several factors affect the success of drilling fluid removal from horizontal annuli. Under static conditions, drilling fluid usually forms a gel structure. Under positive differential pressure, the drilling fluid loses filtrate and forms a filter cake on the formation face. Sometimes the filter cake is mushy and difficult to remove but the formation fluid can easily flow through it. The successful removal of the gel and mushy filter cake depends on the structures that form and how these structures behave under flow conditions. In addition, casing centralization affects the fluid flow profile in the annulus, which affects gel and filter-cake removal. To investigate the mechanism of drilling fluid removal, we conducted both numerical and experimental studies. In the experimental studies, chemical flushes and spacers were tested for their effectiveness in removing drilling fluid. The experiments showed that annulus cleaning begins around the inner pipe and progresses outward at increasing fluid flow rates. Analytical fluid flow models and full 3D multiphase numerical models allowed us to estimate flow profiles and the success of removing drilling fluid under downhole conditions. The large-scale experiments and analytical/numerical modeling have led to a better understanding of the factors controlling drilling fluid removal from horizontal wellbores.

Designing effective zonal isolation for high-pressure/high-temperature and low temperature wells

In recent years, many wells have been constructed that are subject to extreme conditions. Two extreme conditions that can pose a particular challenge during the completion of a well are low temperature, for example in deepwater applications, and high-pressure and high-temperature, encountered in HPHT wells. The products and processes that are normally used to cement wells may be insufficient to create zonal isolation for these extreme conditions. This paper presents methods to help design and execute effective cement jobs for HPHT and deepwater, low temperature wells. First of all, recommendations are outlined for the deepwater conditions. Drilling fluid removal, sealant placement, and sealant sheath strength development are all affected by extreme conditions and are there ore designed accordingly. In order to help determine how strong the sealant sheath needs to be, formation properties are taken into account as well as the operations to be performed during the life of the well. These operations include well testing, stimulation, production, and injection. The paper goes on to discuss the advantages of new products and processes for cement wells under extreme conditions. The laboratory testing procedures, pre-job design procedures, job implementation and evaluation procedures that were used to test the new products and processes are described. Finally, guidelines are given for optimized designs for HPHT and low temperature wells using these products and processes.