Comparison of Lost Circulation Material Sealing Effectiveness in Water-Based and Oil-Based Drilling Fluids and Under Conditions of Mechanical Shear and High Differential Pressures

Abstract

A study was conducted to assess the performance of granular and fibrous lost circulation materials as preventative treatments and in remedial treatment of lost circulation in water-based and oil-based drilling fluids. For the preventative treatments, a factor that introduced increased mechanical wear on the particles was added to the hot-rolling process, to identify signs of deterioration of performance of certain materials. The study of remedial treatments of lost circulation was conducted on slotted discs with apertures of 750 µm and up to 5 mm and with a differential pressure of up to 34.5 MPa (5000 psi). To compare the sealing pressures of the different tests, a simple statistical analysis was introduced to differentiate between the peak holding pressures and the sustainable holding pressures of the various material and fluids combinations. The material degradation studies showed that CaCO3-based lost circulation materials rapidly experienced significant particle degradation after exposure to fluid shear and mechanical degradation and that this considerably reduced the sealing performance of the materials. Also, synthetic graphite-based products showed clear signs in particle size degradation and a significant reduction in sealing performance. Cellulose-based products showed superior resistance toward mechanical wear and only small changes in sealing performance. When comparing water-based and oil-based fluids, it was clear that granular lost circulation materials showed considerably lower sealing efficiency in oil-based drilling fluids compared to water-based drilling fluids. In contrast, cellulose-based materials showed similar sealing performance in oil-based fluids and water-based fluids.