Ball sealers

(74) Agent

Bryns Patentkontor A / S, Oslo.

(56) Cited publications

Norwegian (NO) Patent No. 151558.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealing ball for closing perforations in a casing extending through subterranean formations made with a core of syntactic foam and a resilient coating.

Closing of perforations in a casing is needed when one wants to increase the production rate of hydrocarbons by acid treatment or hydraulic fracturing. For this purpose, sealing balls having a specific weight have long been used which allow the balls to be brought down to the perforations by means of downward fluid flow through the liner. Due to the pressure difference across the perforations, the sealing balls are held in place and closed.

However, the different requirements placed on the sealing balls are difficult to meet at the same time. The sealing balls shall, inter alia, have a very specific specific weight, they should be so rigid that the specific weight does not change with them. pressure that prevails at several thousand meters deep and they should have a durable surface which should however fit well and seal the perforations in question.

A sealing ball of the above type is shown and described in Norwegian Patent No. 151,558. This ball has an elastomeric coating of rubber or similar material.

The sealing ball according to the invention has a core of syntactic foam and an externally resilient coating of poleurethane, this combination having been found to be surprisingly advantageous. By the term syntactic foam is meant; here, a material comprising hollow spherical particles dispersed in a binder, e.g. and resin. The sealing beads of the invention can be used to limit the flow of treatment fluid through the perforations in a lower portion of a well of about 100% efficiency, without affecting the introduction of treatment fluid through the perforations into an upper portion of the well.

Thus, a sealing ball according to the invention is characterized in that the outer coating is of polyurethane.

In the present invention, a sealing ball has been found which is suitable for use in the process of treating a formation described in Norwegian Patent No. 152,467. Broadly speaking, this method involves introducing into the casing of a well perforated at a variety of levels, sealing balls intended to close at least one of the perforations in the casing, and a first fluid of a specific weight greater than the specific weight of the sealing balls, as well as an additional fluid having a specific weight less than the specific weight of the sealing balls. The sealing balls, the first fluid and the second fluid can be introduced into the well simultaneously or in any order. The first fluid is introduced into the well in an amount sufficient to fill the lower portion of the well to a level between the perforations to remain open and the perforations to be temporarily restricted in fluid flow. The difference in specific weight between the sealing beads and the fluid in the well causes the beads to move to the interface or transition zone between the first fluid and the second fluid. As soon as the sealing balls reach below the level to be treated, a treatment fluid is introduced into the well. Fluid flow through the perforations below the sealing beads will bring the sealing beads towards the perforations where the beads will abut the lower perforations and divert further introduction of treatment fluid through the upper perforations. This process can be repeated for processing any number of zones in the formation.

In order to apply the sealing balls according to the invention to the field, it is necessary that the sealing balls have a specific weight which is less than the specific weight of the heavy liquid used and, on the other hand, a specific weight which is greater than the specific weight. for the light fluid, while at the same time the bullets are able to withstand the pressure they are exposed to in the well casing. It is not uncommon for the pressure at the bottom of the well to exceed 700 kp / cm and even 1000 kp / cm during treatment of the well. If a sealing ball does not withstand these pressures, it will collapse, thereby increasing the specific weight of the sealing ball to a value which exceeds the specific weight of the heavy liquid.

The heavy liquid will generally have a specific weight of at least 1 g / cm and the light liquid will generally have a specific weight less than 0.8 g / cm. Therefore, the specific weight of the sealing beads must be in the range of 0.8 to 1.1 g / cm 2, preferably 1.0 to 1.05 g / cm 2.