Evaluation on the Ability of a New Self-Degrading Lost Circulation Agent to Plug Fractures and Protect Reservoirs

When drilling in fractured reservoirs, consideration has to be given to both the plugging of the fractures to control mud losses and the removal of the plugging agents after completion of the well. Conventional temporary plugging agents do not degrade by itself and do not have enough strength to withstand the formation pressures of the reservoirs. A new environmentally friendly self-degrading lost circulation agent SDPF was analyzed for its performance as a lost circulation material (LCM). The self-degrading mechanisms, ability to control mud losses under pressure and reservoir protection by self-removal of SDPF were investigated through pressure bearing test and with Fourier infrared spectrometer, thermogravimetric analyzer (TGA) and scanning electron microscope (SEM). Experimental results have shown that under 25 MPa, the percentage of SDPF that was broken under pressure was less than 5%. The percentage of self-degrading increases with temperature, acidic and basic conditions help accelerate the self-degrading of SDPF, and inorganic salts play no role in the self-degrading of SDPF. A self-degrading mud loss control slurry was formulated with SDPF as the bridging particles and other acid-soluble materials as synergy materials. Micrometer and millimeter sized fractures can be plugged with the slurry, and fractures plugged with the slurry can withstand pressures up to 7.5 MPa. Experiment on the removal of mud cakes and core flowback have shown that rock cores after self-removal of the slurry had percent recovery of permeability of at least 85%. These experimental results have proved that the mud loss control slurry formulated has the ability to control mud losses under pressure and good performance in reservoir protection by self-removal. The development of the new self-degrading LCM is expected to solve mud losses into fractured reservoirs and reservoir protection, two problems that have been difficult to solve simultaneously previously.