Reflections on the Development of Oil Fracturing Technology in China (1
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With the North American shale gas revolution, reservoir stimulation technology is leading the major changes in the global unconventional oil and gas exploration and development. Stimulation has become the three key engineering technologies with geophysical exploration and drilling. China Petroleum 60% to 70% of new reserves of extra-low permeability and low permeability of unconventional oil and gas resources. Special low permeability, deep high temperature, unconventional and offshore oil and other difficult new areas are to be developed and utilized. Transform objects from conventional to unconventional reservoirs reservoir, reservoir properties from high permeability to low permeability, ultra low permeability. The reservoir type is change from conventional oil and gas reservoir to dense gas, tight oil, shale gas, coal bed gas, etc. And accompanied by low pressure, abnormally high pressure, water sensitivity, temperature and other characteristics, the transformation is very complex. With the improvement of the number of wells, the number of layers, the number of segments, the transformation of the reservoir is a large displacement, high pump pressure, large-scale, factory operation characteristics. The changes of fracturing fluid and reservoir layer, the adaptability and cost of the new technology investment put forward new requirements, it is necessary to sort out the oil fracturing fluid technology status and the future development thinking and planning.

Present situation of oil fracturing fluid technology & Application in China

There is no uniform standard for classification and nomenclature of fracturing fluids and named according to the type of thickener. It can be divided into plant gum fracturing fluid type, synthetic polymer fracturing fluid, surfactant s fracturing fluids, and other cellulose fracturing fluids. In this paper, according to the main line of thickener Categories, combining with characteristic fracturing fluid technology, to introduce the technique and application status in oil fracturing fluid.

1.1 Guar gum fracturing fluid

Guar gum fracturing fluid is frozen by the guar collagen powder or a derivative thereof with boron or zirconium formed by crosslinking. Guar collagen powder content of water insoluble is as high as 18% to 25%, the modified guar gum insoluble matter is from 2% to 12%. Guar gum derivatives include hydroxypropyl guar (HPG), super guar gum (SHPG), carboxymethyl guar (CMG), carboxymethyl hydroxypropyl guar (CMHPG), etc.The SHPG is high degree of substitution, purified hydroxypropyl guar gum, which water insoluble is low, and less residue after fracturing fluid gel breaking residue.

Hydroxypropyl guar gum fracturing fluid: Typically at a temperature less than 90 ℃, HPG- inorganic boron crosslinking system is used. When temperature is higher than 90 ℃, HPG- organic boron system was adopted. Through the research and development with new, more efficient crosslinking agent, the formation of an ultra low concentration HPG fracturing fluid significantly reduced the concentration of HPG. It can make 0.15%HPG cross link, breaking the United States fracturing fluid 0.18% lower crosslinking. The relative concentration of the thickener decreased 35-45%, residue decreased 38-53%.

Carboxymethyl hydroxypropyl guar (carboxymethyl guar gum) fracturing fluid: Under alkaline conditions, CMHPG and organic zirconium form fracturing fluid. It equips many advantages such as wide temperature usable (50℃~180℃), low thickener dosage (lower than conventional for 50%), low friction ( lower for 30%~40%), low residue and low residue damage ( lower for 55%), good hanging sand capability etc. Its performance has reached the international advanced level. Also, the acid fracturing fluid system is suitable for alkali sensitive formation and can effectively inhibit the expansion of clay.And it can be applied to CO2 and foam system.

Low molecular recyclable fracturing fluid: The molecular weight decreased after the degradation of the adhesive, 1/20 ~ 1/10 for the conventional. The molecular weight of water insoluble, broken glue, and the damage to the formation of the water are decreased too.

Concentratedly fracturing fluid: To meet the need for accurate measurement of continuous compounding, the guar powder was suspended in a more environmentally-friendly diesel or mineral oil, forming a concentrated liquid thickener.

Overall, guar gum fracturing fluid is most widely used, applications share of more than 90%. But different systems have different degrees of sensitivity to the salt ions in the water distribution system, influencing the properties of fracturing. 

1.2 Fenugreek gum fracturing fluid

Fenugreek gum is a domestic thickener, it is extracted from the seeds of natural plant gum Coumadin. Raw powder of fenugreek gum in water insoluble is 7% to 15%, it equips good water solubility, low friction, the temperature resistance is as high as 170℃. The technical performance of the fenugreek gum is equivalent to the adhesive. But limited by the quality of seeds, processing level, cost pressures and other factors. Currently fenugreek gum fracturing fluid thickener has such disadvantages like high dosage, low temperature resistance and its performance did not meet the technical level has been formed.

1.3 Synthetic polymer fracturing fluid

Synthetic polymer fracturing fluids include two categories of cross-linking and associating. Under the background of the large price increases of the gum, synthetic polymer fracturing fluid technology has been developed rapidly.

Polymer fracturing fluid almost has no residue.Compared with the plant gum fracturing fluid, the solid damage is lower.However, the polymer fracturing fluid is sensitive to water quality and gel.It is difficult to be mixed in the presence of the solution, the supporting agent is not easy to be mixed, the crosslinking control is difficult, and construction friction is high.

1.4 Surfactant fracturing fluids

Thesurfactant fracturing fluid has the characteristics of no residue, easy breaking adhesive, low damage, high elasticity and good sand carrying capability and all the oil fields have been applied.Finally, due to high cost, has not yet obtained a wide range of promotion.

1.5 Oil based fracturing fluid

Oil based fracturing fluid is mainly used for the water sensitive reservoir, which is easy to cause damage by water - based fracturing fluid. Compared with water-based fracturing fluid, it has a high cost, difficult to use, but also the existence of flammable and combustible risk.There is only a small amount usage in Xinjiang Oilfield Applications.

1.6 Characteristic fracturing fluid technology

Emulsion fracturing fluid: Emulsion fracturing fluid is a fracturing fluid system between water and oil base fracturing fluid. Compared with the water base fracturing fluid, the water into underground is reduced. Emulsion fracturing fluid also equips the characteristics of low loss, low residue and high viscosity.The system is used in Haita Daqing, Qinghai, Jilin, Turpan Hami, Xinjiang and other fields of strong water sensitivity reservoir, and achieved good results.

Foam fracturing fluid: Foam fracturing fluid is a mixture of high concentration of liquid N2 or CO2 on the basis of conventional fracturing fluid. It is a low damage fracturing fluid counterpart with the gas phase as internal phase, the liquid phase as external phase.The foam fracturing fluid has a high viscosity, low loss, high residual liquid return rate, especially suitable for low temperature, low pressure, water sensitivity and water lock.The practical application of foam fracturing fluid is not common, the main reason is that the construction equipment is complex and expensive, and the construction cost is high.

Weighted Fracturing Fluid: Improve fracturing fluid density is an effective method to reduce the wellhead pressure construction. Consider cost issues, we use KCl or NaNO3 to HPG- organic boron fracturing fluid system to increase the density.

Thermo-chemical fracturing fluid: The chemical reaction heat is introduced into the water-based fracturing fluid, forming of the self generated thermal foam fracturing fluid. It is used for fracturing in shallow heavy oil , low pressure and low permeability reservoir.

Slickwater: It is a low viscosity and low friction fracturing fluid which is formed by using the drag reducing agent, surfactants, scale inhibitor, clay stabilizer, bactericides, gel breaking agent, anti swelling agent and so on.

About L.E.A.D.

LEAD OILFIELD SOLUTIONS COMPANY is a professional manufacturer and supplier of Sodium Polyacrylate, Corrosion inhibitor, Demulsifierin China. We offer stimulation service and chemicals, acid fracturing engineering. We produce such as clay inhibitor, encapsulated gel breaker, defoameretc. Please visit the company's website at www.sloilfield.com. Connect with L.E.A.D. onGoogle+, and LinkedIn.

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