Fracturing in Unconventional Reservoirs can be Challenging: UAE Case Study

Abstract

Abstract To fracture unconventional reservoirs a different approach is required to be utilized. With the day-to-day advancement in fracturing technology more unconventional formations are being routinely fractured. But now and then we come across formations which challenge modern technologies and make us think out of box. This paper will describe the case history covering the planning and execution of one of the first "Acid-Frac" jobs in UAE. Being the first fracturing job in this formation, no previous stress gradient data was available nor were any leakoff test (LOT) or formation integrity test (FIT) results available at the planning stage. Various aspects of the reservoir and wellbore were considered, core samples of the formation were collected for testing and a 1-D mechanical earth model was developed. The paper will describe the steps taken to prepare the geological model along with the assumptions made. It will also discuss how the uncertainty of stress gradient was tackled while planning the job. Along with the unknown variables about formation, additional challenge was on the surface pressure limitation. Although tree-saver was planned to be used to protect the wellhead, the surface pressure limitation was due to wellbore completion. Based on the various unknowns and limitation on surface pressure, the job was designed. In addition to job planning, this paper will also discuss various lab tests which were conducted on the formation cores to optimally select acid fracturing fluid. Pre-job fracturing model was run with different scenarios which helped to predict if the job could be successfully pumped within the surface pressure limitation. Operation and equipment mobilization was optimized keeping in mind the uncertainties that were predicted. The paper will go into depth covering the different scenarios which were considered while planning the job, vital role of geological model and job execution. Although job execution did not go as per plan, paper will discuss various efforts which were made to establish injectivity and how this job helped in understanding the formation better learning lessons along the way which will be implemented in future campaigns.