Lost circulation prevention or mitigation is a major challenge while drilling. Conventional lost circulation materials (LCM) are often implemented to prevent/cure seepage or partial losses. When it comes to severe losses, often caused by larger fracture sizes, special treatments are being applied. Curing severe losses with specialized treatments requires more time because some treatments can't be applied in the presence of downhole tools, where special equipment and procedures are required. In addition, polymer and cement treatments require time to be activated or cured after being pumped.
Evaluating the performance of LCM and their effectiveness in sealing wide fractures is required in conjunction with an optimized LCM combination to ensure their ability in curing losses. This paper presents investigations about the possibility of sealing relatively large fracture using conventional LCM instead of the other approaches such as cement or hydratable LCM pills. Two specifically developed apparatuses were used to optimize LCM combination and investigate their ability in sealing wide fractures at different pressures. A set of tapered slots that simulate sealable fracture widths with different fracture aperture (2.5 – 5 mm) and tip sizes (1-2 mm) were used in this study.
A total of 160 tests were conducted to optimize LCM combinations and concentrations in addition to 30 tests to evaluate the integrity of the seal formed under elevated pressures with apparatus capability of up to 10,000 psi (69 MPa) fracture differential pressure. The effects of varying LCM's type, concentration, particle size distribution and fracture width were studied with respect to differential pressure and fluid loss. The results showed that LCM's that have irregularity in particles shapes and a degree of deformability such as nut shells are capable of sealing wide fractures when used individually or in combination with other LCM's. In addition, a strong relationship between fluid loss values and the seal integrity was observed, i.e. lower fluid loss, gave higher sealing efficiency.
There is a good potential for conventional LCM's to be reconsidered as a corrective approach for partial or severe losses when the proper LCM's size, type and concentration are selected for a wider range of fracture widths. Curing losses using conventional LCM's for a wider range of fractures widths is advantageous since it can cut time and cost compared to current practices.