| Lost circulation (LC) is an unfavorable event encountered during drilling operations that at extreme situation can jeopardize the whole drilling process. Millions of dollars can be easily accumulated impacting both the economy and the feasibility of such projects. Well control, wellbore stability and stuck pipe incidents are some of the anticipated consequential events caused by lost circulation.;The main objective of this work is to investigate the effectiveness of conventional lost circulation materials (LCM) through 1) studying LCM under a simulated circulation condition (Scirc), mimicking wellbore fluid flow, for fractured formations 2) studying losses in vugular formations experimentally and formulate effective LCM recipes.;To address these objectives, a fluid loss apparatus was designed and developed to simulate field conditions (i.e. the overbalance, difference between mud weight and pore pressure, and mimic circulation). Previously reported effective LCM recipes have been retested conventionally, (i.e. no Scirc ), and under Scirc on tapered slotted stainless steel disks (TS), simulating fractured formations. To study losses in vugular formations, stainless steel disks with different irregular opening shapes and sizes were developed. These disks were used first in a low-pressure LCM apparatus (LPA) with different LCM additives to screen out potential effective recipes. The seal integrity of those recipes was then investigated at higher pressure under an overbalance condition using the developed apparatus.;In this research, LCM blends were tested under a Scirc replicating more of the actual field behavior in fractured formations. The identified effective LCM blends are expected to have an increased success for field treatments. Also this work is considered as the first attempt to study losses in vugular formations experimentally. The results will significantly enhance the understanding of the seal formation in irregular shape openings. |
