Experimental investigation of sealing ability of lost circulation materials using the test apparatus with long fracture slot

Abstract

Lost circulation in fractured formations is a major challenge. The addition of conventional lost circulation materials (LCMs) to drilling fluids is the main method to control loss. The seal integrity is affected by different properties of LCMs. Plugging apparatus with slot is extensively used to evaluate sealing performance of the selected LCMs. In general, the fracture in the formation has depths, and the drilling fluids loss far into the formation. A LCM test apparatus with long fracture slot was introduced in this paper. The main objective of this work is to study the effect of LCM type, concentration and particle size distribution on the seal integrity with long fracture slot. The breaking pressure, fluid loss values, position and thickness of plugging zone are the parameters for evaluating LCM performance. Optical microscopy and scanning electron microscopy were used to observe the arrangement and microstructure of the seal. We can better understand the sealing mechanisms in long fracture by analyzing the cell pressure and fluid loss vs. time plot and the seal structure. Results showed that increasing the LCMs stiffness resulted in higher breaking pressure. There is a critical maximum concentration at which LCM will bridging and filling set at the fracture entrance and no tight seal barrier inside the fracture. Loss effect was beneficial to form thicker plugging zone inside the fracture. Suitable wide particle size distribution of LCM formed thick plugging zone inside the fracture. Multi-layer seal barrier can withstand the external load together, resulted in high seal integrities. The addition of fibrous materials in particles resulted in higher breaking pressure and lower fluid loss.