A major concern to the petroleum industry has been the potential damage to the reservoir and propped fracture system following a stimulation treatment. Possible damage due to the stimulation fluid can exist from residue, fluid retention, or formation-fluid incompatibility. During recent years, a major emphasis has been placed on the development of fluid systems to minimize these possible sources of damage.
By utilizing low-residue gelling agents, potential damage to both the fracture flow capacity and formation permeability in the vicinity of the fracture face should be reduced over that of fluids which contain insoluble residue from the broken gel. Several gelling agents utilizing a variety of base fluids have been developed which possess low residue.
Numerous developments exist in the area of nonaqueous, high viscosity fracturing fluids. These fluids usually high gravity hydrocarbons or alcohol, have been utilized in the stimulation of water-sensitive formations. High gravity hydrocarbons are particularly applicable to water-sensitive, oil producing reservoirs. Their advantages are low residue, low surface tension, and compatibility with both the formation and formation fluids.
Methanol as a base fracturing fluid has met with success when used in low porosity, low permeability, gas reservoirs plagued with slow clean-up and formation damage. However, this fluid is somewhat more costly and often requires the use of specialized equipment. With the introduction of fracturing fluids based on mixtures of alcohol and water, an effective lower cost alternative is now available.
Laboratory tests with formation cores have shown that regained gas permeability is much more rapid following injection of alcohol solutions than when water alone is the injected fluid. This is attributed to a reduction in surface tension and an increase in vapor pressure of the fluid due to the presence of alcohol. In addition, alcohol aids in protecting water-sensitive formations against clay migration and swelling.
Gases, such as nitrogen and carbon dioxide, may be utilized in the fracturing treatment to reduce the amount of time required for clean-up and the amount of fluid retained by the formation. Rapid removal of the treating fluid often lessens the chance for permeability reduction in the formation due to changes in relative saturation clay hydration, or any other formation incompatibility.
During any phase of the drilling and completion of a hydrocarbon producing well, here exists a possibility of formation damage. This paper is concerned with only one of these phases, that of stimulation by hydraulically fracturing the producing formation. Often times, the major benefit of a Hydraulic fracturing treatment may be to fracture through damage created by drilling and completion of the well.
As the industry turns more and more towards drilling wells in low pressure, Low permeability reservoirs, The effects if any damage created during the hydraulic fracturing process are greatly magnified. Because of this, it becomes important for research to be oriented toward eliminating or reducing fracturing treatments. Sources of damage may exist from incompatibility of the fracturing fluid with the formation or formation fluids, fluid retention in the propped fracture and formation, and gel residue or other solids present in the fracturing fluid.