Diversion technologies is becoming widely used as part of multistage fracturing operation and acid stimulation especially in carbonate formations completed with extended reach or multilateral wells. Further importance is gained during the development of unconventional resources where large number of stages are required with enhanced stimulated reservoir volume (SRV) per fracture. This is achieved by improving the fracture network and complexity using far field or deep diversion techniques. Diversion gained more value since it was an enabler for more efficient refracturing jobs since it can divert treatment from existing fractures. One of the main functions of diverters is to direct the stimulation fluid toward the desired treatment interval to increase the efficiency of productivity enhancement process.
A diverter could be either mechanical or chemical. Mechanical diverters include packers, ball sealers, coil tubing, and particulate diverting agents such as benzoic acid flakes, rock salts, wax beads and fiber. Chemical diverter is mostly used as temporary barrier of fluid during treatments, and will get converted back afterwards by chemical means. Chemical diverter can be divided into two main types: polymer-based diverter and surfactant-based diverter. In the past decade, biodegradable diverter has been developed according to the concern of both environmental protection and less formation damage. Relative permeability modifier (RPM) can also be used as diverter in some cases. All the above diversion techniques will either divert the fluid in the wellbore or deep inside the formation based on the objective of the treatment and type of fluid used.
This paper covers diverters in both injectors and producers with the applications of matrix acidizing, acid fracturing and hydraulic fracturing. In matrix acidizing, polymer-based acid gel is one of the most applied diverters. Adding N2/CO2 to form foamed acid, the treatment efficiency could be further enhanced with less formation damage. Viscoelastic surfactant (VES) improved acidizing was also applied in many cases. Fiber based acidizing fluid proposed to be effective in carbonate formation. Multi-stage acid frac jobs were done in 2011 in tight gas carbonate formations. A new trend of acid frac is to use CO2 energized fracturing fluid for tight, sour gas formations. Far-field fracturing mechanism was studied by means of solid particulate diverting agents. Eco-friendly and biodegradable diverters were applied for zonal isolation. Nanoparticles, as new generation of diverters, have been used for EOR as foaming agents since beginning of this decade, especially at HTHP conditions; nanoparticle stabilizers were applied in polymeric gel and VES system to enhance the stability for diversion fluid.
To make the best performance of diverters, limitation on working conditions of each type of diverter would be identified, such as cost, temperature range, pH range, size distribution, and compatibility with fluid additives.