Advanced HPCT Abrasive Perforating Technique Utilized to Successfully Bypass Damaged Formation to Allow for Effective Acid Stimulation
Authors: Malik Ataur R , Al-Bu Ali Mustafa S , Ogundare Tolulope M , Mukhliss Amro E , Green Todd , Haekal Muhammad 
Published: March 2015

This paper will discuss how an advanced technique of abrasive perforating with high pressure coiled tubing (HPCT) was utilized to bypass damage that existed in the open hole section of the well-bore as a result of a recent descaling operation. The well discussed in this paper had extensive scale and therefore required coiled tubing (CT) intervention to clean the wellbore. Following the scale cleanout, a matrix bullhead acid job was performed to bring the well back to production. Some +nonacid soluble scale remained in the wellbore was pushed into the formation ahead of the matrix treatment. As a result, no incremental gains were achieved after the acid treatment.

After analysis of the cleanout, stimulation data and results, it was determined that the cause of the now poor production was scale debris plugging the formation. As the scale was not 100% acid soluble, the team chose to use an abrasive perforating tool with HPCT to bypass the suspected damage. Fifteen stages of perforation were successfully conducted using HPCT Advanced Abrasive Perforating Technique in a single run in depleted carbonate reservoir.

Following the HPCT abrasive perforating operation, good injectivity was reestablished and the well was successfully stimulated to bring the well back to optimal production.

Introduction

In the last few years, the number of de-scaling activities in Saudi Arabia has significantly increased; bringing with it an array of operational complexities such as maintaining optimum circulation conditions and minimizing losses into the formation. The descaling operations generally take place in mature and depleted sour reservoirs where multiple acid fracturing treatments were conducted in the past. The formation is isolated using a large volume of CaCO3 chips prior to mechanical descaling treatment to maintain full circulation during most of the CT intervention period. The size of mill is often limited to 3.5" because of the minimum internal diameter of the wells which makes descaling somewhat inefficient inside the 7" liner. Acid stimulation usually follows these mechanical removal activities to bypass any potential damage into the formation as well as to boost the well productivity. The stimulation treatment often cannot dissolve all the induced damage. Thus, it is critical to bypass the damage through advanced perforation strategy so that acid stimulation becomes more effective by dissolving both damage and etching fresh reservoir rock. The subjected well, highlighted in this paper, has been in the production for 28 years, making it one of the most mature gas wells in the field. Over the years, the well has seen a significant decline in productivity; a decline mainly attributed to reservoir depletion as well as to the scale precipitation in both sandface and inside the wellbore. The well was worked over in 2002 and a new tubular were installed before re-perforating and acid fracturing the existing interval. Ten years later, iron sulfide (FeS) scale accumulation in the tubular was detected and confirmed by running a series of gauge cutters only for the 3.25 in size to tag scale at shallower depths.