During the completion of a well the utilization of a propellant stimulation system immediately after or at the time of perforating has been demonstrated to provide sufficient stimulation energy to cleanup formation damage in the near wellbore region while remaining within the desired zone of interest. The focussed and virtually instantaneous nature of this technique means that it can be used in applications where more aggressive stimulation techniques may result in the increase of undesirable fluid production due to stimulation extension into adjoining regions. Propellant stimulation devices provide an inexpensive and effective method of dealing with near wellbore damage due to drilling, completion, or perforating in both producing and injecting environments.
Standalone propellant stimulation techniques have been successfully utilized for a number of years in various areas of the world. The recent development of a propellant assisted perforating system means that the perforations and near wellbore region can be effectively stimulated at the instance of perforating. This advanced perforating system fuses perforating and propellant stimulation devices into a hybrid system - the well can be perforated and the near wellbore region stimulated all with one run in the hole. The development of propellant stimulation modeling software and high-speed electronic pressure recording devices has assisted in the development and verification of the technique's effectiveness in removing or reducing near wellbore damage.
This paper will discuss the development history of this unique perforating and stimulation technique and the new analytical tools used in its advancement and ongoing application. A number of case histories are presented documenting the use and effectiveness of the stimulation method in a variety of environments and applications.
Propellants can be defined as explosives that deflagrate rather than detonate. Detonation propagates a shock wave through the explosive, whereas deflagration chemically burns the material. The deflagration of the propellant generates a volume of high pressure combustion gases that can be utilized to stimulate the near wellbore region of a reservior without risk of damaging the formation as is the case with explosives used in the process of perforating a well11.
Originally propellants tools were configured as standalone devices and run in the well after the interval had been perforated. The objective of the propellant stimulation was to remove near wellbore damage, which in a number of instances could be attributed to the perforating process. The development of a propellant-assisted perforating system eliminated the additional procedure as the perforating and stimulation operation could be undertaken simultaneously with the objective of generating more effective perforations at the time of perforating.
The propellant-assisted perforating system employs a cylindrical sleeve of propellant that is slid over the outside of a conventional hollow steel perforating carrier (Fig. 1). The system is conveyed in the well either on wireline or tubing, depending on the application or stimulation interval length. Once positioned on depth, detonating the shaped charges ignites the propellant sleeve. The pressure wave generated by the charge exits through the carrier and penetrates the propellant sleeve and the casing, forming a perforation tunnel in the formation. The perforation is already formed before the propellant begins to generate gas.
As the propellant burns, a surge of high-pressure gas is produced that enters the newly created perforation and breaks through the damage around the tunnel, extending fractures from the perforation. When gas pressure in the well bore dissipates, gas surges back into the well bore carrying damaging fines from the formation.