Lubov Abdulayevna Magadova, Doctor of Eng. Sc., Technical Director of Khimeko-GANG is answering our readers questions.

 

 

Polysaccharide fracturing fluids are the safest and the cheapest, as they are based on water. Yet, it is necessary to take into account that, as it gets in terrigenous reservoir, the fresh water may prompt clay swelling. Meanwhile, the use of mineralized formation water, which does not bring about clay swelling, is not always possible because of the complications with polysaccharide jellifying. The latter is sensitive to multivalent cations, present in the formation water.

 

Some companies, for instance, Сlеarwater, suggest using special additives to fresh water reducing clay swelling. Yet, our researches (Gubkin Russian State Oil & Gas University) showed insufficiency of these additives. Only increase in clay stabilizer NCL-100 content in water gel from the recommended 2 l/m3 up to 10 l/m3 allows receiving the bentonitic (Sarigukhsky) clay swelling equal to the level of swelling in the formation water of calcium-chloride type with the density of 1012 kg/m3. At the same time, adding 20 kg/m3 of cheap potassium chloride into the fresh water allows settling all the problems with clay swelling. That is why working in mudded reservoir, sensitive to water, needs fresh water with potassium chloride to be prepared as fracturing fluid.

 

Service companies apply several types of destructors: peroxide destructors, pellet destructors, enzymes. Peroxide destructors (ammonium, natrium and potash persulfates) are used more frequently. For dosage during operations fracturing, the peroxide destructors should be preliminary dissolved in water. It is necessary to point out that ammonium persulfate is better dissolved in water. That it is why it is more

popular. Yet, highly concentrated water solutions of such aggressive media as peroxide destructor solutions bring about strong corrosion of dosing tools leading to their breakage.

 

Experience suggests that auger-type dosage of the destructor is the most suitable. When it’s the case of little amount, dry mixture with potassium chloride is recommended.

 

The advantage of a linker with deferred linkage is that it reduces friction loss, when it is pumped into the well, since gel viscosity increases gradually and the maximal viscosity is recorded at bottomhole level. High speed of pumping makes the proppant remain in suspended state. At the same time lower friction loss results in lower well mouth pressures, and this is a better guarantee of a successful operation.