Recently, there has been significant interest in understanding the material properties of lost circulation materials (LCM), including size degradation studies from mechanical compression tests and from shear flow. These types of tests are currently of particular importance because of increased drilling activity in mature fields, which often require LCMs as a background material. The objective of this work is to present the size degradation of LCMs from flow loop tests.
A flow loop test was performed to study the size degradation of LCMs, mainly ground marble (GM) and resilient graphitic carbon (RGC). A predetermined amount of GM and RGC was added to an 80-bbl synthetic-oil-based drilling fluid. The flow loop consisted of 3-in. diameter flow lines. One circulation through this flow loop required approximately 8 minutes, which is equivalent to one circulation in the actual field application. The fluid with LCM was circulated through the flow loop at a 400-gal/min flow rate. Fluid samples were collected at different stages, and a wet sieve analysis was performed to determine the amount of material in the drilling fluid retained on each sieve. Comparing the amount after the flow with the amount before flow allowed estimations of the LCM size degradation. This provided the size degradation the LCM would experience as a result of flow through the loop.
Another objective was to study the effect of a turbine, which was anticipated to be part of the bottomhole assembly (BHA) on the size degradation rate of LCMs. To evaluate this, a turbine was incorporated in the flow loop, and the fluid with LCM was again circulated at a 400-gal/min flow rate. Again, samples were collected at different times, with a wet sieve analysis performed to determine the size degradation of LCMs when flowing through the turbine and the flow loop.
GM was subjected to a 35% size reduction resulting from the flow loop alone, compared to only a 16% size reduction of the RGC. When the turbine was added to the flow loop, GM was almost completely degraded (a total of 75% reduction) to a smaller size after only one circulation through the loop. Concurrently, the RGC experienced only a 20% reduction in size even after 160 minutes of flow (20 circulations) through the loop and the turbine.
Size degradation studies of LCMs were conducted for the first time in a flow loop at a 400-gal/min circulation rate. The results show the importance of using a resilient LCM, such as RGC as part of a LCM background package when drilling lost circulation problem zones in mature fields.