NO324113B1 - Concrete mix for use in oil and gas wells - Google Patents

Abstract

Concrete mixture for use between casing and rock wall in a borehole adapted for exploration for or production of oil or gas, or arranged for maintenance of such exploration or production holes, where the concrete mixture due to the pressure of said gas or oil or surrounding structures or due to the depth of the hole below a sea level must withstand high pressure while the specific gravity of the concrete mix is regulated by the concrete mix containing a specific gravity aggregate material with a specific gravity less than the specific gravity of cement, in order for the liquid concrete to exert a pressure on the surrounding structure. self-weight-regulating aggregate material are compact glass balls.

Description

This invention relates to a concrete mixture for use in oil and gas fields, more specifically a mixture consisting of a significant proportion of glass spheres with a preferably rough surface. The purpose of the invention is to provide a compressive concrete with a low specific gravity.

When using concrete, it is necessary in some contexts to reduce the specific weight of the concrete mixture in order to reduce the stress on surrounding structures during the casting phase. A close example of this is the cementing of an oil well. Concrete is used here to fill the space between the borehole casing and the bedrock through which the hole passes. Some rock structures are unstable and can collapse if exposed to a hydrostatic pressure from liquid concrete that is filled around the casing. The consequences of this can be large, unwanted cracks in the formations around the borehole.

In order to reduce the specific gravity of the concrete mixture, it is used today, among other things, fly ash as aggregate material in the form of balls with a diameter down to 0.25 mm. The fly ash provides the desired opportunity for regulating the specific weight of the cement mixture, but the properties of the fly ash make it of little use when purposes other than a reduced specific weight are desired. Fly ash is a by-product from the combustion or processing of e.g. silica. It often contains substances hazardous to health. However, the fly ash's inability to withstand high pressure is of greatest importance to the properties of the cement mixture. Already at a pressure of approx. 60 bar (800psi) collapses the fly ash. This results in settlements in the concrete before solidification and thus an increase in the specific weight of the concrete.

The purpose of the invention is to remedy the disadvantages of known technology.

The purpose is achieved by features which are indicated in the description below and in subsequent patent claims.

In a concrete mixture intended to be filled between an oil or gas well's casing and the surrounding rock wall or between pipes of different diameters, aggregates known in and of themselves such as cement, water, sand and possibly density, viscosity and solidification regulators are used substances.

In order to reduce the specific gravity of the concrete mixture, glass particles have been mixed into the water, for example of the product type Liaver Super-K from Liapor GmbH & Co KG, Hallendorf, Pautzfeld, Germany, in the form of mainly glass balls with a diameter of 0.25 - 0.8 mm . Liaver Super-K is delivered with different specific weights, typically from approx. 0.45 to 2.5 g/cm<3>. The most used type has a specific gravity of 0.45 to 1.0 g/cm<3>.

The preferably most used types of glass particles have a specific gravity which means that they remain floating or, if the water is kept in a stirring motion, suspended in water. When the glass particles are liquid or suspended in the water, an even distribution of the glass particles is ensured when the water/glass particle mixture is added to the rest of the aggregates during the concrete mixing process.

According to the invention, the specific gravity of the concrete mixture is regulated by using a type of glass particle with a specific gravity that at approx. 30% glass admixture by volume gives the desired concrete density according to the needs of the casting assignment. In this way, the concrete mixture can be used under conditions where the pressure on surrounding structures must be minimized.

The glass particles have a compact cross-section. The surface is preferably rough.

Concrete mixed with glass beads of the Liaver Super-K type has high compressive strength. Concrete mix testing shows a crushing of 0.3% of this type of glass beads at a pressure of close to 1100 bar (15000 psi) and a temperature of 175<2>C. In this way, a concrete mixture according to the invention exhibits small settlements during solidification and high compressive strength in the hardened state.

The surface of the glass particles in their preferred spherical shape exhibits a great ability to adhere to cement. When pumping a concrete mixture containing glass beads, it has been shown that wear on pump and pipe details is reduced by lowering the total abrasiveness of the aggregate mixture. Cement-coated glass beads exhibit a reduced grinding effect compared to the other main components of a concrete mix. At the same time, the concrete mixture's ability to flow through pipes and the like is improved, whereby the power requirement for pumping is reduced.

In tests, the concrete mixture according to the invention shows little shrinkage and strong adhesion to steel. This achieves a good connection, for example, between an oil/gas well's casing and the surrounding concrete.

Glass has a relatively high heat capacity. During the concrete's solidification and hardening process, the high heat capacity has a dampening effect on the temperature rise that naturally occurs in this phase. Especially in wells where gas condensate occurs in a frozen state, the aforementioned effect is of great importance. An increase in the temperature in the gas hydrate can lead the gas to vapor form, which leads to a strong volume expansion. The expansion may result in damage to technical installations in and around the well. The use of glass particles in the concrete mixture will thus reduce the risk of such damage during casting work in boreholes.

In what follows, a non-limiting example of a preferred embodiment is described which is visualized in the accompanying drawings, where: Fig. 1 shows an illustrative and greatly enlarged glass particle suitable for use in a concrete mixture according to the invention.

Reference is made to figure 1, where a spherical glass particle 1 of the type Liaver Super-K 1 in a particle surface 3 exhibits several recesses 2 of varying shape.

A concrete mixture according to the invention consisting of

36.25 1 seawater with specific gravity 1.025 g/cm<3>

4.5 1 CaCl with specific gravity 1.314 g/cm<3>

30 1 glass balls Liaver Super-K 1 with

specific gravity 1,000 g/cm<3>

100 1 G cement with specific gravity 3.220 g/cm<3>

showed a specific gravity of 1.71 g/cm<3> in the wet state. After solidification under 69 bars (approx. 950 psi) pressure, the specific gravity showed 1.71 g/cm<3>.

Laboratory tests were carried out in which a concrete mixture I suitable for the purpose according to known techniques is compared with a concrete mixture II according to the invention. A summary of several repeated tests shows the following measurement results: The measurement results showed that the concrete mixture according to the invention has produced the expected effect on compressive strength and adhesion.

Claims (5)

1. Concrete mixture for use between casing and rock wall in a borehole designed for exploration or production of oil or gas, or designed for the maintenance of such exploration or production holes, where the concrete mixture due to the pressure from said gas or oil or surrounding structures or on due to the depth of the hole below sea level, it must withstand high pressure at the same time that the specific gravity of the concrete mixture is regulated by the fact that the concrete mixture contains a specific gravity-regulating aggregate material with a specific gravity less than the specific gravity of cement, in order for the liquid concrete to exert an appropriate pressure against the surrounding structure of the borehole, characterized by the specific weight-regulating aggregate used in the concrete mix consists of compact glass spheres (1). 2. Concrete mixture according to claim 1, characterized in that the proportion of glass balls (1) constitutes up to 40% of the total volume of the concrete mixture. 3. Concrete mixture according to one or more of the preceding claims, characterized in that the specific gravity of the glass balls (1) is between 0.45 and 2.5 g/cm<3>. 4. Concrete mixture according to one or more of the preceding claims, characterized in that the diameter of the glass balls (1) is between 0.25 and 0.80 mm. 5. Concrete mixture according to one or more of the preceding claims, characterized in that the glass balls (1) have a rough surface (2).