Clay Removal And Cut-point Curve Analysis of a One-step Solids Control Equipment: Theory And Field Application
Authors: Malekzadeh D. , Hayatdavoudi A. , Ghalambor A. 
Published: March 2010

Abstract
The objective of this paper is to evaluate the performance of a One-step Solids Control Equipment (OSSCE) based on the actual field data. The material balance technique was used to achieve this objective. The data obtained consisted of density, volume flow rate, solids content, and size distribution of the mud in each flow stream of OSSCE. The cost-effectiveness of using OSSCE as compared to mud cleaners was investigated using the actual field data obtained upon running the same mud from the shale shaker underflow through the two equipment. In addition, the cut-point curve for each equipment was obtained.
The results indicated that the cost of using mud cleaner on the mud sample analyzed is about 4.5 times higher than that of OSSCE if a 3% reduction in volume per cent of low gravity solids is desired and assuming a higher efficiency for both equipment due to less solids loading after each run of the entire mud system through each equipment. In our opinion, this is a reasonable assumption that will ensure that the 0.9% and 0.27% net reduction in volume per cent of low gravity solids calculated for OSSCE and mud cleaner, respectively, during the first run of the entire mud system is achieved at subsequent runs. The cost difference is due to the fact that the mud cleaner discarded only 1.7 times more low gravity- solids than weight material while OSSCE discarded 4 times more low gravity solids than weight Material. Results indicated that very high recovery efficiencies for commercial additives such as barite, lignite, and iron oxide were obtained using OSSCE.
Based on mineral analysis, approximately 31 % of very small amounts of Chlorite that entered OSSCE (only 2% by volume of total clay minerals that entered OSSCE belongs to Chlorite) was discarded-by concentric discharge and screen overflow discharge. This high per cent by volume of Chlorite discarded may be attributed to its high density, small size, shape, and flocculation of Chlorite particles. The lowest per cent by volume of clay type discarded belongs to Kaolinite (3%), which may be due to the lesser amount of flocculation by this clay type and/or its size, shape, and low density. Finally, the results indicated that the cut-point curve will shift to the left as the volume flow rate of screen overflow discharge increases, resulting in sharper particle separation or lower d50. Therefore, the volume flow rate of the screen overflow discharge can be adjusted to obtain the desired cut-point.

Introduction
Drilling fluid is a major factor in the success of any drilling operation, and the key to any effective mud system is good solids control. Solids control is one of the most important phases of mud control on every well.
Mud solids consist of particles which come from the formation being drilled and other particles which are added to the mud to control chemical and physical properties. The material added to the mud include:clay additives such as bentonite,weight material such as barite, andvarious chemicals to control rheological and filtration properties.