Hydraulic fracturing has proven to be extremely beneficial for almost all different kinds of reservoirs in the Western Desert of Egypt, with approximately 70% of the production resulting out of this stimulation technique. However, a deterrent to fracturing in many cases has been the proximity of the producing zones to underlying (or overlying) water zones, either located near the water-oil contact or the producing zones adjacent to water bearing zones. In the absence of geological barriers, the fracture height can grow uncontrolled during a fracturing treatment into the water-bearing interval and cause unwanted water production after the job. Excessive water production threatens the economics of a well by shortening its production life as the water production dominates over the hydrocarbons production and traps the reserves behind, increasing disposal and lifting costs, boosting the fines migration, increasing the rate of tubular corrosion and scale build-up. Many times in marginal fields, these can be sufficient reasons not to consider fracturing or its benefits at this time will not be economical.
Some reservoirs are not produced without fracturing or producing naturally at uneconomical rate. These kinds of wells are the best candidate for this technique once we encounter water-bearing zones above and below.
Since this technique is incorporating with hydraulic fracturing so it has been named as Conference while fracturing or CWFrac service. The oil industry has used permeability modifiers since the 1970s. They have been primarily used to reduce the water production coming from water-fingering, water-coning, early water breakthrough in water-injection reservoirs, and water coming from high permeability water streaks.
One great advantage of the RPMs in reducing water production is that they only decrease the relative permeability-to-water with little to no effect on the relative permeability-to-hydrocarbon.
The RPM used in this technique has certain advantages over other RPMs that have been introduced previously in the industry. Primarily it is a water-soluble polymer combined with water-insoluble alkyl chains (retaining the overall water solubility), otherwise known as a hydrophobically modified polymer.
A hydrophobic modification is a water-soluble polymer with small groups attached that are not water-soluble. Because only a few of these groups are attached, the polymer is still soluble in water. However, because these groups are hydrophobic, they tend to attract each other and repel water molecules. This could almost be called a crosslinking mechanism, although it is a weak association. This is why a hydrophobically modified polymer has increased solution viscosity. This weak association also leads to increased levels of adsorption (Fig. 1). The bottom layer of lines represents polymer molecules adsorbed onto a rock surface. With a normal polymer, this is all that would result. There is no driving force for more polymers to adsorb onto the first layer. However, with the hydrophobically modified polymer, the hydrophobic associations cause more polymer to adsorb (as demonstrated by the dashed lines in Fig. 1), and this is why higher levels of water-permeability reduction occur with this polymer.
This polymer, once it is pumped into the formations, adheres immediately to the formation grains and begins to work immediately. Incorporating this chemical as padding before the hydraulic-fracturing treatments helps to stimulate marginal reservoirs, where the possibility of crossing water zones near the hydrocarbon zones is very high. This technique yields good results. The mechanism of permeability reduction is based on restriction of the water-flow path in the matrix of rock without harm to effective oil permeability (Fig. 2)
Rami Yassine Country Manager, Production Enhancement
Amr Azzam Account Manager, Business development
Ahmed Ali Technical Prof. Frac/Acid