Measurements of rock parameters

Abstract

Methods and apparatus to measure physical parameters such as density and porosity of the rock matrix in a near wellbore area are provided. A borehole tool having a number of transducer elements in a transducer array is placed at an outermost surface of the borehole tool and is capable of emitting focused high frequency ultrasound beams into the rock matrix in the near wellbore area. The transducer array may be placed on the ribs or stabilizers of the borehole tool, and / or on a sleeve with a lower rotational speed, and may include a fronting material with similar acoustic impedance as the rock matrix. A method for measuring physical parameters of the rock matrix in a near wellbore area is also provided where a focused high frequency ultrasound beam is emitted into the rock matrix in the near wellbore area from one or more transducer arrays on a borehole tool.

Description

FIELD OF THE INVENTION[0001]The present invention relates to methods and apparatus to measure physical parameters such as density and porosity of the rock matrix in a near wellbore area as well as the type(s) of fluid present in the near wellbore area.BACKGROUND[0002]In geological exploration and development, formation evaluation indicating the physical properties of a volume of rock next to the borehole is used to determine e.g. whether a potential oil or gas field is commercially viable. Extrapolation of the properties beyond the measurement volume further requires a geological model.[0003]Physical properties of the near wellbore rock are generally evaluated by measurements-while-drilling (MWD), Logging-while-drilling (LWD), by different wireline tools or combinations hereof.[0004]Measurements-while-drilling (MWD) in general covers the collection of directional data enabling well trajectory description in three-dimensional space while extending the wellbore, and also includes pres...

AI Technical Summary

Benefits of technology

[0014]According to one aspect the present invention relates to a borehole tool for performing measurements in a wellbore comprising a number of transducer elements in at least one transducer array placed at an outermost surface of the borehole tool for emitting at least one focused beam of high frequency ultrasound into the rock matrix in the near wellbore area when in use. Hereby is obtained a borehole tool capable of measuring different physical properties of the rock matrix in the near wellbore area, such as for instance densities and porosities. By the use of focused beams of high frequency ultrasound information of the rock matrix of very high resolution is obtainable. These parameters can thus be determined with a far better accuracy and precision than with traditional measuring techniques resulting in better information for finding, evaluating, and exploiting oil and gas fields. The use of ultrasound is also advantageous in making the use of the highly dangerous and polluting radioactive sources superfluous, ultrasound on the other hand posing no risks to the personnel handling or manufacturing the borehole tool or to the environment when in use.

[0017]In a further embodiment the transducer array(s) is placed on a sleeve of the borehole tool with a lower rotational speed compared to the drill string. This is advantageously in that measurements can then be made on a stationary or near stationary environment, minimizing dynamic effects, regardless of the motion of the rest of the borehole tool.

[0021]Also, in one embodiment the borehole tool according to the further comprises a processor for influencing the functional parameters of the transducer array(s) such as frequency, amplitude and / or focal point position of the emitted focused beam. Hereby is obtained a borehole tool where the measuring parameters can be optimized continuously whereby better, more reliable and more precise results can be obtained.

[0031]In yet a further embodiment the method comprises applying one or more correction filters to generate near perfect focus of the emitted beam. This step also acts to improve the precision of the measured data

Problems solved by technology

Further, many wellbores prove to be difficult or even impossible to measure with conventional wireline tools, especially highly deviated wells where hole stability issues may be time critical.

Most wireline measurements are recorded continuously while the sonde is moving, however certain fluid sampling and pressure-measuring tools used for formation sampling require that the sonde be stopped, increasing the risk that the sonde or the cable might become stuck.

According to established knowledge all radiation represents a health hazard.

Despite all security efforts performed when applying the method described above employing radioactive sources, the potential health risks as well as the environmental disadvantages of the method provide powerful incentives to develop alternative methods to measure indirectly or directly the rock density and porosity excluding the use of radioactive sources.

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