Lessons Learned from Stimulation Treatments and Filter Cake Removal Practices in High Permeability Carbonate during the Drilling Phase

Abstract

Abstract In permeable carbonate formations, hydrochloric (HCl) acid treatments are usually utilized to remove formation damage and mud filter cake induced by drilling operations. Usually, the practice is to implement these stimulation activities after the rig is released and permanent completion is set. In some cases, these stimulation treatments cannot be performed due to tight project schedules and the need to deliver production/injection targets on time with minimum risk and environmental impact. These unique scheduling issues dictates stimulating the well before landing the production string and while the rig is on-site to save rig time and minimize expenditures. Yet, stimulating the well in this situation will increase its injectivty, which may lead to severe lost circulation problems and potentially serious well control issues. The objective of this paper is to present several field cases designed to achieve effective stimulation treatments while combating the issues of lost circulation. Several stimulation recipes were studied in the lab and deployed in the field trying to address the goals of having a recipe that provide stimulation mechanism with the highest safety commitment and controlled investment. For example, acidic brine with different HCl concentrations, enzymes and organic acids were used. These recipes were applied during the cleanout trips after reaching total depth of the well. Therefore, they were used to displace the drilling mud out of the hole. As the displacement began, immediate lost circulation (100 barrels per hour (bph) to 150 bph) took place, which hindered well safety. Losses were beyond the rig pump capabilities and mandated immediate curing processes with Hydroxyethyl Cellulose (HEC) Polymer pills, which damaged the well again. This paper details the experience gained from stimulating more than 10 wells where acidizing jobs have been performed before running the completion. It discusses efforts and techniques utilized to stimulate these wells but allowing the rig to perform casing clean out, mud displacement, pulling out assembly, and running the completion without encountering losses. Normally, this process takes an average of 3-to-5 days to complete. Subsequently, all tried stimulation recipes caused early lost circulation with varying degrees of severity. Lessons learned from these treatments are studied in this paper. These lessons were beneficial in optimizing and integrating stimulation and drilling activities. These synchronized efforts proved realized cost savings and fast turnover of wells.