Evaluation of polymer free drill-in fluids for use in high productivity, horizontal well completions

Abstract

Advancements in deepwater drilling have necessitated the use of more specialized reservoir drill-in fluids (RDIF). These RDIFs must exhibit unique rheological properties while minimizing formation damage. Xanthan gum biopolymer is generally used as a primary viscosifier in RDIFs. In high salinity brines the high shear rate viscosity that xanthan gum provides can approach levels that could exceed the fracture gradient of the well. Therefore, it is important to maintain a xanthan gum concentration that keeps the equivalent circulating density at a modest level. Reducing the xanthan gum level, however, compromises the hole cleaning properties that the low- shear-rate viscosity provides. Xanthan gum biopolymers are also associated with formation damage, which inhibits the flow of oil and gas during production. A new RDIF, which utilizes no xanthan gum biopolymer, has been recently developed. The new product uses a starch instead of polymer to develop rheological properties. This fluid will primarily be targeted for production zone drilling in highly deviated and horizontal wells. This research focused on filtercake cleanup and the reduced formation damage associated with this biopolymer-free fluid. The behavior of the polymer free fluid was analyzed developing tests at different temperatures, at different drill solids content, and with different treatment fluids. The laboratory methods used were a ceramic disc cell and a linear flow cell. The former will permit an analysis of the time that a certain cleaning treatment takes to flow through a filter cake. The latter simulates well completions in unconsolidated horizontal well reservoirs permitting the estimation of formation damage produced by drilling and completion fluids and the effectiveness of the cleaning treatment applied. Multivariate statistical analysis was performed with the experimental results obtained. Comparison with conventional RDIF data from polymer carbonate and sized salt fluids provided informative contrasts in performance.