The effect of wellbore circulation on building an LCM bridge at the fracture aperture

Abstract

Different laboratory experimental setups with slotted disks, simulating fractures’ apertures, have been used extensively to formulate effective loss circulation materials (LCM) recipes. The amount of fluid loss and sealing pressure have been used as the evaluation criteria. The question still remains is how valuable these tests are when LCM fluids are circulated in the wellbore to stop losses. The main objective of this work is to study the effect of the annular fluid flow on building an LCM bridge at the fracture aperture.To address the objective, a fluid loss apparatus has been developed to mimic wellbore circulation. Tapered slotted disks were placed upward in a cylinder filled with drilling fluid and LCM additives. Drilling fluid is pumped at the bottom of the cylinder and the wellbore circulation is simulated through the use of stirring paddle. Previously reported effective LCM recipes have been retested conventionally, no simulated circulation, and under simulated circulation condition (Scirc) with varying pump flow rates and tapered slotted disk sizes. A new term, sealing effectiveness ratio (SER), is introduced to effectively evaluate the sealing integrity of the LCM recipes at the Scirc.The results showed when stirring the sample, a higher fluid loss was required before the sample sealed and the maximum sealing pressure (Pmax) was lower than sealing pressures reported from conventional tests. Different LCM recipes required a different minimum flow rate for a seal to initiate at the Scirc. Increasing the flow rate improved the sealing effectiveness ratios of all LCM recipes. At high flow rates some recipes gave very similar Pmax as conventional tests while others lost more than 35% of their strength. At a given flow rate with larger opening size slot, the effect of Scirc was amplified as higher fluid loss was required to initiate a seal and a lower sealing effectiveness ratio was recorded. The most significant new finding is that LCM with lower specific gravity was less prone to the Scirc making them better preventive approach candidates.