Expandable, Acid Soluble and Settable LCM for Severe Losses

Abstract

Loss of circulation during drilling and cementing operations is a very common yet challenging problem. It often causes large amounts of non-productive time (NPT) and inadequate zonal isolation. One of the main reasons why such losses are difficult to remedy is the lack of knowledge about accurate fracture width and depth encountered while drilling, leading to an improper selection of suitable plugging materials that can adapt, in both volume and shape, to effectively plug a wide range of fractures with unknown dimensions.Traditional, non-reactive particulate/fiber based or settable fluid, types of loss circulation materials (LCM), when applied in insufficient quantities, cannot effectively seal a high permeability zone. Whereas, the series of settable and acid-soluble LCM fluids developed in this work are expandable in nature; therefore, the LCM can adapt in volume even under high downhole pressure to effectively seal a wide range of fractures with unknown dimensions. Volume adaptability is introduced in the LCM through in-situ generation of non-hazardous gas; in the gas phase, the LCM can either expand or contract depending on the differential pressure at the fracture space.The fluids developed in this work are applicable up to a downhole temperature of 149°C (300°F). An HTHP cement consistometer has been used to determine the pumpability time of each LCM fluid to ensure that they do not setup prematurely while pumping. A set-delaying agent is used to adjust the pumpability time. The LCM fluid starts in-situ generation of the non-hazardous gas above 49°C (120°F) while pumping down the wellbore. Laboratory testing has been performed to quantify the percentage of expansion at different temperatures, demonstrating that the rate of gas generation is faster at higher temperatures. Acid solubility has been tested with 15% HCl and the LCM is 100% soluble. In-situ formation of gas in these fluids is non-flammable and non-hazardous, unlike earlier industrial attempts that release hydrogen gas. The expandable nature of this acid using soluble and settable materials makes it novel and unique in that it can expand, even under down-hole pressure conditions, to effectively cure major losses at application temperatures up to 149°C (300°F).