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Formation gas pore pressure evaluation on drilling cuttings samples

Formation gas pore pressure evaluation on drilling cuttings samples description/claims

This application is a continuation-in-part of U.S. patent application Ser. No. 10/711,469 filed Sep. 20, 2004, which is incorporated herein by reference in its entirety.

The present invention relates generally to apparatus and process for obtaining formation pore pressure from a drilling cuttings sample, thereby reflecting the physical and petrophysical properties of the formation drilled for oil and gas or other targets. These measurements are obtained at the surface. While drilling, the mudflow brings the cuttings to the surface and, from the cuttings samples, the process and apparatus of this invention are employed in producing the information.

During the drilling of a well, mud circulates downhill and brings up formation cuttings of the strata penetrated at this time. After the lag time related to the annular velocity and the depth of the well, the cuttings arrive at the surface. At the surface a sample catcher device, disclosed by the author in patented U.S. Pat. No. 6,386,026 B1 May 14, 2002, captures the material and at this time the apparatus and process disclosed in this invention measure the physical, physical-chemical and petrochemical properties of the formation.

Conventionally grinding the sample or steaming it and measuring the gas extracted by using gas detectors with catalytic combustion sensors do some of the cutting gas extraction. We disclose the ways to obtain the Emission=V/P=mm3/Pa, Total Volume=V=mm3, Maximum Pressure=P=Pa of the samples of the drilled strata.

Apparatus and process of this invention are provided for obtaining the specific properties of the drilled formation or any descried formation sampled. The apparatus and process for measuring the formation gas pore pressure on drilling cuttings samples in the test tube can be defined as follows:

The apparatus includes a vertical holder for a test tube, a test tube for placing the cutting sample and a pipette for adding a measurable quantity of liquid. (Note: “vertical holder for test tube and test tube” are disclosed in U.S. application Ser. No. 10/711435 published 20050063050 Horizontal Binocular Microscope for vertically gravitated and floating samples) which is incorporated herein by reference.

The process includes measuring the gas bubbles size and volume in the test tube and the height of liquid covering the bubble. With this information, the volume and the pressure of the gas emitted out of the pores is calculated. The pore size is measured by the grain sieve of fraction in the test tube. As the sample is very fine grinded (by mortar and pestle) the size may be assumed as the statistic average of the mass. This initial volume of gas in pore and the final volume in test tube are related by v1/p1=v2/p2. By adding/subtracting more liquid to the sample and increasing/decreasing the height and the pressure of the liquid on the pore, the test is repeated and the measurements documented in the tables for math processing to obtain the error corrections and standard deviation of the measurements. The results are expressed in Emission=V/P=mm3/Pa, Total Volume=V=mm3, Maximum Pressure=P=Pa.

It is an object of the present invention to obviate or mitigate at least one disadvantage of previous methods and apparatus for determining pore pressure.

In a first aspect, the present invention provides an apparatus for measuring the size and the height of a bubble in a drill cutting sample including a sealable container adapted to receive the drill cutting sample, a liquid, and a pressurizing vapor, pressurizing means for varying the pressure of the pressurizing vapor in the container, level means for varying the level of the liquid in the container, and vibration means for vibrating the drill cutting sample.

In one embodiment, the pressurizing means includes a source of compressed pressurizing vapor.

In a further aspect, the present invention provides a method of determining the gas pore pressure of a drill cutting sample, including receiving a grinded sample in a container, the grinded sample having fine particles, the grinded sample being obtained by grinding a drill cutting sample taken from an earth drilling process, substantially separating discrete media of the grinded sample by grain size, receiving a liquid in the container, the liquid covering the grinded sample to an initial liquid level at an initial pressure, increasing or decreasing the pressure in the container to produce a bubble or vary the size of a bubble of gas within the sample, measuring the size of the bubble and the pressure, and calculating the gas pore pressure.

In one embodiment, the discrete media of the grinded sample are separated by vibration. In one embodiment, the discrete media of the grinded sample are separated by sieve. In one embodiment, the discreet media of the grinded sample comprise sandstone, siltstone, and shale.

In one embodiment, the method further includes calculating a volume based on a spherical bubble and determining an emission from the formula—emission=volume/pressure. In one embodiment, the steps of varying the pressure, measuring the size of bubble and pressure, and calculating the gas pore pressure repeated for a subsequent bubble after the initial bubble. In one embodiment, steps of varying the pressure, measuring the size of bubble and pressure, and calculating the gas pore pressure are repeated for a subsequent pressure after the initial pressure. In one embodiment, the subsequent pressure is greater than the initial pressure. In one embodiment, the subsequent pressure is less than the initial pressure. In one embodiment, the initial pressure is atmospheric pressure. In one embodiment, the size of the bubble is measured by the measurement of the bubble diameter by microscope. In one embodiment the container is a test tube. In one embodiment, the liquid is a substantially clear liquid. In one embodiment, steps of varying the pressure, measuring the size of bubble and pressure, and calculating the gas pore pressure are repeated for a plurality of cycles for bubbles and/or pressures, to determine an error correction and standard deviation.

In a further aspect, the present invention provides an apparatus for measuring the size and the height of a bubble. The apparatus includes a vertical holder for a container, for example a test tube, the test tube for placing the cutting sample and a pipette for adding a measurable quantity of liquid.

In a further aspect, the present invention provides a process of measuring the size and the height of the bubbles. The pore size is measured by the grain size of fraction in the container (for example a test tube). As the sample is very fine grinded (by mortar and pestle) the size may be measured by sieving it and then taking the statistic average of the mass weight versus the sieve size. By applying the above method using 2-3 different sizes as necessary the high accuracy will be achieved.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

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