Proposta de uma correlação para cálculo da perda de carga e diâmetro hidráulico no escoamento de suspensões e selamento de fraturas

Abstract

During drilling operations it is usual to find natural or artificial fractures on the wellbore; these fractures allow the drilling fluid to flow into the rock formation. This phenomenon is called loss of circulation and it increases cost of the operation and may threat the structural integrity of the well. In order to combat this problem it is necessary to understand the flow of fluids through fractures and develop methods to mitigate the loss of circulation. This work proposes a new model for correlation between the pressure drop and the volumetric flow of fluid through fractures. A physical simulator was used to collect experimental fluid flow and pressure drop data in fracture with 2, 5,10 mm of aperture and 1,02 m long. A LCM made of a mixture of polymers and calcium borax was added to the fluids to study the sealing of fractures. Density, rheological behavior, composition and particle size test were performed to characterize the studied materials. The lost circulation material had bimodal particle size distribution and the formulated fluids had a Herschel-Bulkley rheological behavior. Experimental flow and characterization data were used to propose a correlation between pressure drop - volumetric flow and to develop a new methodology to monitor the sealing of fractures by calculating the decrease of hydraulic diameter throughout their healing. The suspension with lost circulation materials went through filtration tests to observe the effects of sealing particles on the mud cake and filtrate volume. The proposed correlation pressure drop and volumetric flow was able to model the flow of fluids though fractures with low experimental deviation. The methodology to monitor fracture sealing was able to calculate the hydraulic diameter and the filtration tests showed that the lost circulation material particles are filtration control agents.