Nanoparticles in Weighted Water Based Drilling Fluids Increase Loss Gradient

摘要

Drilling fluid composition can greatly influence the stability of a wellbore. This paper discusses the effect that a nanoparticle drilling fluid has on the formation loss gradient. Creation of nano-barite was performed by mechanical and chemical means and comprised 3% by weight of the drilling fluid. A hydraulic fracturing unit was used to determine the core breakdown and fracture reopening pressure of low permeability core samples. Using both a typical water based drilling fluid, part of the barite particles where mechanically and chemically created as nanoparticles. The fracturing test cell and low permeable core samples measuring five by eight inches were confined to typical in-situ stress conditions throughout the wellbore pressuring up and fracturing process. The results obtained from the hydraulic fracturing experiments can be analyzed evaluating the pressure versus time curve. Analysis of these curves show that the breakdown pressure for three fluid samples yielded roughly the same value, yet the fluids with chemical and mechanical nanoparticle additives showed a 4% and 15% increase in reopening pressure over the base case. Application of the reopening pressure increase seen in nanoparticle weighted drilling fluid can be shown for a theoretical equivalent field case where fluid loss gradient in the dominating casing design criteria. Applying a 15% increase to the loss gradient as seen with the application of mechanical nanoparticles in the drilling fluid would provide a larger area for a casing program to be designed and has the capability to lessen the overall number of casing strings. From these experiments it can be seen that the addition of barite nanoparticles to drilling fluid has the potential to greatly alter the margin between pore pressure and the loss gradient under in-situ conditions.