Horizontal Well Productivity Restoration - Successful Stimulation Application in a Large Onshore Field

This paper discusses the step by step procedure to identify damage mechanism and remedial treatment in horizontal wells flowing with ESP (Electrical Submersible Pump) in one of the largest onshore field Mangala situated in Barmer, Rajasthan, India. Mangala field was discovered in 2004 and was brought on production with hot water flooding in August 2009 and is currently producing at plateau rate of 150,000 bopd (barrels of oil per day). The reservoir, in general, is of high quality with multi-darcy permeability, relatively viscous (15cp) and waxy crude (wax appearance temperature only 5 deg C below reservoir temperature). The Fathegarh is the main reservoir unit which is sub-divided into FM1 (top) to FM5 (base). FM3 and FM4 are dominated by well-connected sheet flood and braided channel sands having net to gross ~80%. These massive FM3 and FM4 sands have been developed with down-dip edge water line drive water injectors and up-dip horizontal producers. These horizontals wells (lateral length >500m) are completed with screens with ICD’s (Inflow Control Devices).The initial PI (productivity index) of wells has been of the order of 50-100 b/d/psi. However, with rise in water cut and increased withdrawal rate the productivity of these horizontal wells started to decline. This paper discussed the optimized production practice required to maintain optimum production rate from these horizontal wells. Due to the fact that even relatively shallow invasive near-wellbore damage may substantially impede flow; plan was prepared to identify the damage mechanism and accordingly engineer suitable remedial treatment. Envisaged damage mechanism included fines mobilization, asphaltene / wax dropouts and carbonate and sulfates scales. An inherent problem with these wells was poor acid distribution during matrix acidizing, especially due to high permeability in long horizontal sections. The low cost systematic stimulation design and placement technique resulted into the liquid PI restoration and improved ESP performance, which has been discussed in length in the paper.