A Large Aperture Test Apparatus for Severe Lost Circulation Material Evaluation
Authors: Ramasamy Jothibasu , Amanullah Md , Al-Arfaj Mohammad K 
Published: October 2018

Failure to have a reliable and adequate evaluation method and apparatus for materials used to combat severe lost circulation causes the drilling industry to have significant non-productive time due to frequent failure to control moderate to severe loss circulation. Apart from losing whole drilling mud while drilling, lost circulation can lead to additional problems such as differential sticking, borehole instability and also well control situation if not controlled properly. There are different types of lost circulation materials such as fibrous, flaky, particulate, polymers or their blends developed to mitigate severe mud losses. However, the non-availability of a reliable apparatus for simulating the loss zone and an appropriate testing method for evaluation of materials for severe loss scenarios make the selection of proper loss control materials very difficult and thus in most cases treatment of severe lost circulation is addressed by trial and error basis. Hence, the conventional severe loss control method has very low probability of success. In order to address this on-going problem, there must be a method and apparatus to evaluate and validate products for lost circulation based on the loss zone characteristics relevant to severe loss circulation problems. The paper describes a reliable test method and apparatus capable of simulating fractures and vugular zones up to 40 mm for screening and evaluating lost circulation materials for moderate to severe loss of circulation problems. The test apparatus is made of several components such as a test cell, a mud reservoir, a spacer/activator reservoir and a LCM reservoir. All these components are engineered and assembled in a systematic way using various fixtures such as ball valves, relief valve, connecting pipes, pressure inlet, fluid outlet and various discs with slotted and circular openings/holes to simulate various loss zones. The test cell is capable of holding a slotted metal disk having slots up to 40 mm to represent a fractured loss zone and discs with a circular holes to represent a vugular loss zone. The test apparatus has been designed to test various LCM products up to 600 psi working pressure. The reservoir chambers containing mud, spacer and LCM slurry are individually connected to 500 psi pressure lines to push the material from reservoir chamber to the test cell whenever required. Once the desired material is placed inside the test cell, the ball valve connecting the test cell chamber and the reservoirs is closed. The test can be carried out up to 600 psi to evaluate the blocking efficiency of the materials. The material passing through the slotted or circular hole containing discs will be collected through the outlet in the bottom of the test cell. The amount of material collected through the outlet will be used to evaluate the performance of the LCM. The newly developed test method and apparatus will play a vital role in screening of different materials for lost circulation and selection of right material based on the loss type. Therefore, it is expected to have a positive contribution in trouble free and safe drilling operation.