There is a place in the stimulations/sand control area for non-aqueous systems, particularly for water sensitive formations. The non-aqueous systems include hydrocarbons gels. Non-aqueous alcohols provide several advantages in terms of formation compatibility, retained conductivity, cleanup and enhanced productivity. In addition to operational difficulties, several technical challenges are posed when non-aqueous alcohols are considered for fracturing/gravel pack gels.
Conventional wisdom indicates that guar or guar derivatives will not gel non-aqueous alcohol systems. The alcohols are considered anti-oxidants. Thus, oxidizers are not expected to break non-aqueous polysaccharide gels. Based on these factors, several monograms and text books on fracturing fluids have categorically stated that it was impossible to gel non-aqueous alcohol with guar based polymers and that there was no known way to degrade pure methanol-based gels at temperatures below 32 C.
This paper presents against conventional wisdom with a new technical avenue for a new non-aqueous alcohol based gel that can also be broken very efficiently at moderate to high temperature (50 C to 120 C). A non-aqueous gelled alcohol fracturing/gravel packing fluid based on a guar derivative that can be crosslinked and energized is described. The unique system meets the rheological requirements for fracturing and can be broken using an unique oxidizing breaker system.
In the stimulation of oil and gas wells, hydraulic fracturing has established itself as a useful and economic requirement in the industry. It has also been established that proppant transport and retained conductivity to be the two most important parameters of fracturing fluids. It is generally assumed that viscosity is one of the prime requirements for not only proppant transport but also optimum fracture width and length. To obtain maximum results from a fracturing treatment, it is essential to obtain maximum retained conductivity from the treatment. Several factors that contribute to this are, recovery of maximum amount of the treatment fluid, complete and clean break of the gelling agent and prevention of formation damage from fracturing fluid interactions (such as clay migration, swelling and emulsion and/or fluid blockage of pore throats). These interactions can extend into the formation if leak off of the fluids cannot be controlled. However, these factors are generally balanced with available technology, economics and safety among other factors.
Conventionally, water or hydrocarbons have been used as base fluids for fracturing. Over the years, several authors have identified the advantages of alcohols over these fluids. These includes, but are not limited to, the low freezing point, low surface tension, high water solubility, high vapor pressure and formation compatibility of methanol. The three concerns with methanol are all related to safety: the low flash point, high vapor density and the invisibility of flame. With special precautions, as previous authors have identified methanol can be safely used in the field.
Several approaches to gelling methanol have been described in the literature (3-4, 6-8). These include foams of methanol to gelling with synthetic polymers (Polyacrylamide and PEO) and modified guar. Attempts were also made to crosslink the gelled methanol with metal crosslinkers.