Annular fracturing of multiple zones with coiled tubing (CT) has been practiced for more than a decade. A typical treatment involves sand jetting perforating, cleaning the well, fracturing and isolation. It is economically desirable to perforate, fracture and isolate each interval quickly, allowing all intervals to be treated in the shortest time possible. However, CT lying on the bottom of horizontal wells creates a solids bed during the perforation and fracturing stage, this introduces additional complexities into the reliable execution of the fracturing process. For tight formations, proppant beds have to be completely or partially removed, otherwise the pad can entrain the proppant which creates a high potential for premature screen out.
In this paper, a new approach to cleaning the hole between multiple annular fractures is proposed. This hole cleaning process involves circulating the clean fluid through the annulus to the bottom of the wellbore and bringing the sands back to the surface through the CT; at the same time the CT pulls out of the hole (POOH). The sand particles at the top section of the wellbore are swept toward to the end of CT, while the solids near the end of the bottom hole assembly (BHA) are sucked into the CT as it is pulled out of hole. Eventually, all solids are removed with the CT partially pulled through the initial bed section. As a wiper trip to surface is not required, the efficiency of this new process is higher than other cleaning processes. A full scale flow loop was used to simulate the process. Maximum POOH speed and the hole cleaning time were determined under various conditions. Empirical correlations were developed to allow for optimization of the process under the down hole conditions.