Large-particle-size (d_(50) > 300 μm) lost-circulation materials (LCMs) are often used to plug large fractures and manage downhole losses. They are usually added to a fluid to form a pill, which is pumped downhole. If downhole temperatures are high, these large particulates can settle out of the fluid, likely resulting in unsuccessful LCM treatments. This paper discusses temperature-stable fluids that suspend large LCMs and, thereby, efficiently address this challenge and mitigate lost circulation at high temperatures. A detailed experimental study was conducted to study the rheology-vs.-temperature behavior of several fluids up to 325°F on advanced rheometers/viscometers. The suspension of large LCMs in these fluids at these temperatures was studied experimentally in a lab environment. The same LCM-fluid combinations were also investigated using the standard laboratory permeability plugging apparatus (PPA) tests at high temperatures. The slotted disc in a PPA simulates the fractures in the wellbore, and the slot plugging test is widely used in the industry to test the plugging efficiency of LCM particulates. The temperature effect on the rheology of the fluids was demonstrated by plotting rheology-vs.-temperature data obtained from the rheometer/viscometers at various applied shear rates. The rheological investigation showed that fluids designed with certain combinations of viscosifiers provided stable rheologies (only a slight drop in rheology with temperature) at high temperatures. During the suspension tests, these temperature-stable fluids demonstrated a superior ability to suspend the large LCMs at high temperatures. The information agreed with the quantitative correlations in the literature on rheology requirements of the fluids to suspend given LCMs. The temperature-stable fluids also improved the LCM performance during the PPA tests, indicating their potential to mitigate losses effectively in high-temperature wells.
展开▼
