A Breakthrough in Controlling Lost Circulation in a Pay Zone by Optimizing the Particle Size Distribution of Shellfish and Limestone Chips

Abstract

The most common drilling problem experienced by drilling engineers is lost circulation, which results in great expense to oil companies because of either drilling fluid supply or subsequent drilling problems like pipe sticking. It becomes more challenging when dealing with heavy mud weights as high as 165 pounds per cubic feet (pcf). To resolve this problem, lost circulation materials (LCMs) are added to the drilling fluid in order to diminish mud loss rate to an acceptable level. Different types of LCMs in use in the drilling industry are employed based on the circumstance. The situation becomes worse when drilling in the reservoir section. In such intervals, the added materials should have the capability to be off the formation when the well is put on back flow or they should be soluble in acid in order to prevent reservoir impairment and reduction in productivity. In this study, it is tried to find the optimum size range of limestone and shellfish for use as LCMs in fractured and loose formations. Six different sizes of limestone and six different sizes of shellfish were used with four various slots and sleeves (simulating distinctive formations) for assessment of loss stopping efficiency. An oil-based mud in a bridging material testing apparatus was utilized at several differential pressures and temperature of 16°C, but because in overbalanced drilling a differential pressure of 200 psi is more likely to be employed, tests were conducted at a pressure of 200 Psig. After performing numerous tests with different sizes of LCMs, a remarkable decrease in mud loss was observed when using a particular size of LCM according to formation type and optimum LCM concentration.