Gazprom Performs First Multiple Hydraulic Fracturing in Carbonate Reservoirs

A multiple hydraulic fracturing operation has been performed for the first time on a horizontal well drilled into carbonate reservoirs* in the East area of Orenburg oil and gas condensate field, operated by Gazprom Neft Orenburg, a subsidiary of Gazprom Neft. The operation was performed as part of Gazprom Neft’s tight reserves program.

The drilling of horizontal wells using multiple hydraulic fracturing is the key technology for development of tight reserves. This technology makes it possible to complete several hydraulic fracturing operations on the borehole of an individual well in order to increase oil recovery by impacting individual strata one at a time.

Acid multiple hydraulic fracturing involves metered injections of a special gelatinous compound and inhibited hydrochloric acid into the stratum. During the first stage, a viscous layer fills the cracks in the reservoir. Subsequent acid processing makes it possible to accomplish deeper penetration of the compound into the stratum. The treated channels remain open, which allows for the cracks to have a high throughput and increases the influx of oil into the well.

Hydraulic fracturing in the East area of Orenburg oil and gas condensate field consisted of five stages. The length of the horizontal section reaches 600 meters. A total of two hydraulic fracturing operations were performed on two separate production wells. After completion of the operations, the combined average flow rate of both wells will add up to approximately eighty tons of oil per day. The wells are functioning via natural flow.

“The method we’re using to raise oil recovery helps increase the flow rate of horizontal wells significantly by bringing larger quantities of reserves into development. The results we achieved clearly demonstrate that we can successfully apply acid multiple hydraulic fracturing at new wells to enhance the development of the East area of Orenburg oil and gas condensate field,” says Gazprom Neft Orenburg CEO Alexei Ovechkin.

The East area of Orenburg oil and gas condensate field is a unique and one of the largest fields in the Orenburg region. Development of the field is complicated primarily by its geological characteristics, since fractured carbonate reservoirs with a high gas/oil ratio and hydrogen sulfide content predominate at the field.

Reservoirs are rocks that contain empty spaces within, are permeable, and in which water, oil, and gas can move under the effect of gravity and an overburden pressure differential. Terrigenous reservoirs are composed of sand, siltstone, sandstone, siltite, certain types of argillaceous rock. Fifty-eight percent of the world’s discovered oil reserves and 77 percent of gas reserves are associated with reservoirs of this type.

There are only two main rock-forming minerals in carbonate reservoirs: calcite and dolomite. Oil and gas filter through them primarily via cracks and caverns. Carbonate reservoirs, unlike terrigenous reservoirs, can be substantially improved in terms of their filtration properties and storage capacity by means of artificial treatment with solutions of hydrochloric acid and carbonated water, as well as through other methods that take advantage of the chemical reactivity of the calcite and dolomite.