In a mature oil field, many wells have low productivity. In one oil field in South Sumatra, most of them produce 150 bpd and 7 bopd. Some of the wells initially produced 300 bopd with 20% WC. Previous engineers had tried to treat the wells with acid stimulation to increase relative permeability. The others treat the wells by adding more perforation. Sometimes, a frac pump is used to do hydraulic fracturing.
Several questions must be answered before choosing an appropriate treatment for the well. How much is the remaining reserve around the well? How about the decline rate? What kind of productivity damage is there? Stimulation or Fracturing?
Formation damage is complex. Sometimes, preventing formation damage is more expensive than doing a treatment to cure the damage. A compatibility test is important to avoid the worst damage after treatment. Precipitation, scale build-up are some side effects due to incompatible treatment fluid with formation fluid. Also, be careful with the size of the particle inside the treatment fluid. The particle can block pores and prevent the treatment fluid to touch the formation. Some companies use expensive pieces of equipment to filter completion fluid and treatment fluid.
Frac pump sometimes is used to pump stimulation fluid to pre-saturate formation with VES (visco elastic surfactant) to prevent formation damage. Before fracturing or matrix acidizing, the formation is soaked by VES where the VES contains viscosity enhancer, temperature stabilizer, and the internal breaker. The viscosity enhancer will enhance elasticity where at the static condition the VES has high viscosity but at dynamic condition has a low viscosity. As of the name, the temperature stabilizer is for stabilizing the VES viscosity against the formation temperature.
The internal breaker is the improvement of the previous method of using VES. It is believed that without an internal breaker, the VES will stick onto the formation pore and can not be removed all by well unloading. The internal breaker will break the VES which will be easily unloaded during well flowback.
In fracturing, the VES will occupy a high permeability area including fractured formation and prevent loss of fracturing fluid to that zone. The fracturing fluid which delivers by a frac pump will then frac low permeability area. The same situation is achieved during matrix acidizing. Without VES, the acid will acidize the high permeability area and leave the low permeability area untreated. VES will occupy the high permeability area and divert the acid to the low permeability area.
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