Innovative Solution to Minimize Oil-Based Mud Formation Damage in Jurassic Depleted Reservoirs
Authors: Anood Al-Dhafiri , Yousef Al-Otaibi , Taha Bloushi , Majdi Al-Mutawa , Moudi Al-Ajmi , Mamoun Abdelbagi , Sebastian Sierra Martinez , Mohammed Abdel-Basset 
Published: February 2024

Abstract
This document describes how the use of filter cake breaking fluid pills in non-cemented completions across North Kuwait Jurassic reservoirs increased the well's likelihood to be stimulated and produced. It describes the process to test this innovative solution before a well trial, the wells and environment in which they have been used, and their impact in the well's ability to communicate the borehole with the reservoir. The initial step was to identify which type of mud breaking pills could be used and available in the industry and use the current OBM dispersant pills as found in cement job spacers to enhance cement-reservoir contact. A target well screening was done to wells with possible non-cemented reservoir completions. The detailed operational procedure was then designed to consider the breaker volumes, the composition of the interface's spacer high viscosity pill, and the weight of the displacement fluid to account for the hydrostatic loss in the solids-free breaker volume into each of the wells’ geometries. Finally, these wells were stimulated and tested to identify if the new approach had enabled the wells to be productive and minimize the OBM's damage.
The solution has been applied in three barefoot and two multi-stage completion wells. The first well's 380 ft 3-7/8" carbonate reservoir took 18 days to drill using 12.1 ppg OBM. Several calibration trips were done and on the final trip the 30 bbl mud breaking pill was displaced to replace the OBM within the open hole section. Post injectivity tests and an acid treatment, the well's initial production was 3 times the field average with a stabilization above field average gas production. In the second well, the 460 ft 3-7/8" section took 7 days to drill using 11.6 ppg OBM. This fluid was left in the hole to perform the acid treatment without achieving any injectivity. The entire reservoir section was then displaced with the mud breaking solution, for which injectivity and successful acid treatment and N2 activation achieved a final production rate comparable to the offset wells. In the third well, the 684 ft 3-7/8" reservoir took 3 days to drill with a 11.5 ppg OBM, which was displaced with the mud breaking pill using the drilling BHA before pulling it out of the hole. The well achieved immediate injectivity and higher than field average production. The fourth well's 676 ft had a 1578 ft section with a 4-1/2" stuck uncemented liner 1000 ft in the 6" OH. This well was left with 13.6 ppg OBM during 1 year and left unproduced. A reentry was done to mill the shoe, clean the uncased open hole and displace the entire section with 11.6 mud breaking fluid. A posterior injection was successfully applied achieving production results above field average on an area in which local offset wells had deemed the formation as tight.
The first multi-stage completion pilot was also trialed, in which the OBM weight was initially lowered from 12 to 8.8 ppg, and then displaced by the breaker fluid prior to set the hanger and activate the packers. Following this implementation, a second well with MSC completion was also performed in a 703 ft, 6" section. After a 19 day soaking period of the breaking fluid in the annulus between the MSC and OH, injectivity and stimulation operations were successfully carried out with low surface pressure requirements.
The use of filter cake breaking pills in barefoot wells achieved the purpose of facilitating the communication between the wellbore and the reservoir, requiring lower stimulation pressures, and minimizing formation damages that positively impacted the wells’ productivity.