Master of Science in Petroleum Engineering (MSPE)
Oil and natural gas resources in the deepwater Gulf of Mexico are important for the U.S. economy, but development is limited by high costs. Dual density drilling concepts that result in wellbore pressure gradients similar to the natural subsurface gradients can simplify well designs and reduce costs. Riser dilution may be an economical means of achieving such a system. This system would use a low density fluid to dilute the weighted wellbore fluid and give an intermediate density fluid in the riser. Two key concerns addressed in this study are whether a drilling fluid can be formulated that will suspend solids and transport cuttings after dilution and whether the fluid returning from the riser can be separated into wellbore and dilution fluids for a continuous process. The first concern was addressed by laboratory testing of synthetic-base drilling fluids. The wellbore, riser, and dilution fluids were formulated with the same synthetic fluid to water ratio and liquid phase product concentrations with only the barite concentration, and therefore density, being different. Formulations with good emulsion stability over the maximum density range needed for real deepwater applications were developed. However, appropriate rheologies for the extreme case of 17.0 ppg wellbore fluid and 9.5 ppg riser fluid were not achieved with laboratory muds. Separation testing was conducted to address the second concern using a laboratory centrifuge and hydrocyclones. The laboratory centrifuge demonstrated that practically all barite could be removed from the dilution stream and retained in a wellbore stream, but also that the wellbore stream rheologies were excessively high. Hydrocyclone results implied the need for two stages of separation. The most successful two stage trial gave less contrast in densities than the laboratory centrifuge, but gave better rheologies and emulsion stabilities than either the laboratory fluid or the laboratory centrifuge tests. Also, the rheologies from hydrocyclone testing were only slightly less than the rheology values considered necessary for a working riser dilution system. Both the density contrast and the rheologies were also close to the best centrifuge results published by others working on similar systems.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Shelton, John, "Experimental investigation of drilling fluid formulations and processing methods for a riser dilution approach to dual density drilling" (2005). LSU Master's Theses. 282.
John Rogers Smith