Abstract
Lost circulation materials (LCMs) are added to drilling fluids to mitigate lost circulation (LOC) problems. Designing the fluid requires a good understanding of sealing mechanisms and all the parameters affecting the sealing performance. Laboratory testing apparatus is the key concept for LCM evaluation ensuring successful treatment. The high-pressure test cell containing fracture discs is an effective tool among the broadly designed apparatus. A variety of formulations has been developed from the LCM physical properties. Recently, the testing conditions such as the slot wall angles and the fracture disc thickness were found to have significant effects on the evaluation results. However, the effect of the base fluids, fluid density, types of weighting materials and aging conditions has not been addressed. In this study, two different base fluids, water-based fluids and oil-based fluids, were used to compare the base-fluid effect. Drilling fluid density was raised up using barite and/or hematite to investigate the effect of the weight agents. Barite was sieved to study the effect of fine particles on the sealing. Finally, the dynamic aging tests were conducted in LCM-treated WBF using two temperature levels (200 °F and 400 °F) and two aging periods (24 and 72 h). The results showed that the base fluids affected the sealing performance depending on the complex interaction between the solid particles and the fluids. Adding weighting agents tended to improve the seal integrity. Adding proper size of fine particles improved the LCM sealing performance. Aging conditions affected LCM properties depending on the thermal stability of the materials.
Highlights
Lost circulation (LOC) is a challenge for many drilling operators
The sealing pressure in the G, Sized calcium carbonate (SCC) and Cellulosic fiber (CF) and (G and SCC #1) formulations increased by approximately 50% when used in oil-based fluid (OBF) compared to water-based fluid (WBF)
With previous work of Jeennakorn et al (2017) and the observation made in this study, the sealing mechanism could be further explained
Summary
Lost circulation (LOC) is a challenge for many drilling operators. It significantly increases drilling expenses due to the loss of massive amounts of drilling fluids and potentially loses expensive downhole equipment or even the entire well. Laboratory studies were continuously and comprehensively run to understand how LCM works, how to evaluate the performance, and how to improve the sealing ability in the field application (Scott and Lummus 1955; Abrams 1977; Nayberg 1986; Dick et al 2000; Hettema et al 2007; Kageson-Loe et al 2009; Kefi et al 2010; Clapper et al 2011; Alsaba et al 2014b, c, 2016). Focusing on fracture sealing in the impermeable rock matrix, Alsaba et al (2014c, 2016) presented the effects of LCM type, shape, concentration, particle size distribution (PSD), and temperature on the seal integrity with respect to differential pressure at different fracture widths. The experiment was continuously run using the high-pressure LCM tester as an evaluation method (Alsaba et al 2014b, c, 2016)
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