TYPES OF PROPPING AGENTS USED IN HYDRAULIC FRACTURING

Oil recovery from layer and any impact on it are carried out through wells. The Bottomhole Zone of Layer (BZL) is the area in which all processes proceed most intensively. Efficiency of mining, outputs extracting, acceleration performance delivery and that share of sheeted energy which can be used on raising of liquid directly in the well significantly depend on a condition of a bottomhole zone of layer.

In case the layer is put by jointed well hardpan breeds, the mechanical methods of influence, the most widespread of which is hydraulic fracturing, can be applied to increase oil or gas recovery.

The Hydraulic Fracturing (HF) is a process of influence of liquid directly on breed until it doesn't begin to collapse and process of formation of cracks will begin. HF is carried out by pumping gap liquid to layer (gel, water or acid) under pressure exceeding pressure of disclosure of cracks [2].

The first Hydraulic fracturing was in the Hugoton field in the state of Kansas in 1947. This fracturing treatment contained river sand from a nearby river. The fracturing fluid was gasoline, gelled with World War II surplus Napalm. This river sand was used to hold open the created fracture. This proppant was of poor quality and the volume was small. Even though specialists have had tremendous debates and discussions stating that proppant is not needed, the overwhelming evidence supports the need for some type of material to hold open the created fracture or fractures to allow for the ongoing production of hydrocarbons.

For the subsequent half a century rather large number of various wedging agents have been tested: steel fraction, aluminum granules and high-strength glass balls. In addition to the above mentioned river sand, one of the more interesting early day propping agents was particles of Walnut Hulls. In the early days of hydraulic fracturing it was felt that all fractures propagated horizontally at bedding planes. The idea of the usage of the soft Walnut hulls is that they would be easily transportable, i.e. they would float. And that under pressure of the closing fracture face they would compress rather than crush.  And used at low concentration would leave infinitely conductive flow paths for hydrocarbons to produce through. The use of Walnut hulls as a functional material was fairly short lived due to the fact that the vast majority of fractures were vertical and the walnut hulls would float and converge and with closure would create something akin to fiber board which has virtually no permeability.

As a result of HF, the wells output's increasing by decrease in hydraulic resistance in a bottomhole zone and increase in a filtrational surface of the well raises multiply. Final oil recovery also increases because of familiarizing with development of poorly drained zones and seams [4].

The entity of hydraulic fracturing is formation and extension of cracks in layer creating of high pressures on a well bottom by the liquid downloaded in a slit. In the formed cracks the sorted coarse-grained sand or proppant are forced. Proppants are the spherical granules retaining of cracks created by HF from interlocking under the big pressure and providing the necessary productivity of oil and/or gas wells by creation of the carrying-out channel in the layer [2].

An additional positive effect can be achieved when used as a liquid breaking foam based on acid. Hutchins and Miller reported classification of gas/liquid mixtures based on quality. When quality ranges below 52%, it is classified as energized fluid as dispersion; wet foam is classified as foam quality between 52 % and 74 %; dry foam is classified as foam quality between 54 % and 96%; and mist is classified above 96 %. Generally, the higher the quality of a foam, the higher the viscosity and interfacial structure of foam bubbles. In low quality foams below 50 %, the bubbles touch each other and allow less freedom of movement within the total fluid. In high quality foams above 75 %, the bubbles are crowded together and no longer have spherical shapes. Movement within the fluid is very restricted; resulting in high apparent viscosity results Foam texture refers to bubble-size distribution of the dispersed gas phase. Qualitatively, it describes the distribution of small/large bubbles and homogeneous/heterogeneous nature. Foams are normally formed in systematic hexagonal texture as a result of gas dispersion through a continuous surfactant solution. [6]

The formed new cracks in the layer or which have opened and the extended available ones, connecting to others, become the conductors of oil and gas connecting the well remoted from a well bottom with productive zones of layer. The extention of cracks deep into of layer can reach several hundred meters [4].

Now in HF operations the following types of propant are used:

• natural quartz sand;
• aluminosilicate ceramic propant (on the basis of bauxites, kaolins and their mixes);
• magnesia-silicate proppants (based on serpentinit, olivinit and their natural mixes);
• RCP with a polymeric covering (both ceramic, and quartz sand) [6].

The ceramic agglomerated bauxite is high-strength proppant which is made of qualitative bauxite or kaolinic ores. Process of production includes ore crushing, compaction into spherical particles and roasting in the furnace at the high temperature causing agglomeration process. The final product usually contains up to 85 % of Al2O3. Other 15% make oxides of iron, titan and silicon. [1].

RCP downloads to the well at a final stage of HF for the purpose of prevention of the return carrying out of proppants. There is a strong coupling of them due to polymerization of a covering under the influence of high temperatures and pressure. High values of permeability are remained even when exposed to the polymeric covered propants of high pressures.

The use of the proppants in hydraulic fracturing is a necessity. Since 1947 a great job has been done, however it is necessary to make the further improvement of production technologies and an assessment of efficiency, and a search of new materials.

Список литературы:

1. ГОСТ 51761— 2005. Пропанты алюмосиликатные. Технические условия. – Москва: Стандартинформ, 2006.
2. Меликбеков А.С. Теория и практика гидравлического разрыва. - М.: Недра, 1967. - 141 с.
3. Папков С Новое поколение проппантов для ГРП. // Журнал Neftegaz.ru – № 7-8 - p. 80-81.
4. Khristianovich S.А. Researches of the mechanism of hydraulic fracturing // Institute of geology and development of combustible minerals. – М., 1960. – V.2.: Materials on development of oil and gas fields.
5. Malpani R., Holditch S.A - The gap liquid choice for a production intensification from low-permeable gas-bearing layers // Oil and gas technologies. – 2008. -№11. - p. 51-55.
6. Hutchins, R. D., and Miller, M. J. 2003. A Circulating Foam Loop for Evaluating Foam at Conditions of Use. Presented at International Symposium on Oilfield Chemistry, 5-7 February, Houston, Texas. SPE-80242-MS.