METHOD AND EQUIPMENT FOR RECORDING AND PROCESSING DIGITAL IMAGES OF DRILL CORES

Abstract: A method for recording and processing digital images of a slabbed drill core (10), is characterised in that the images of the drill core (10) are recorded directly by means of a high resolution, digital camera (9) moved in equal intervals along the drill core (10). While the records are taken, the drill core is illuminated by a constant light in a direction having an angle ( alpha ) with respect to the surface of the drill core, as the digital recorded data are transferred to a computer (6) for further processing and storing.

Description: Method and equipment for recording and processing digital images of drill cores The present invention concerns a method and equipment for recording and processing digital images of drill cores taken from subterranean geological formations. Recording and processing should here be understood as digital photographing and recording, together with handling, showing and statistical analysis of such images by means of suitable data equipment and software. While performing drilling operations for oil and gas, there are frequent taken up samples such as drill cores from formations that may contain oil- and/or gas. The drill cores are subjected to different investigations to determine the petro-physical properties of the formations from which the cores are collected, that will say petro-physical properties related to porosity, permeability, grain size and grain size distribution, sand and clay relations, together with the quantification of main minerals in sand stone. Previously it has been known to take ordinary colour pictures in scale 1:5, 1:4 and some times 1 :2, of slabbed drill cores under the influence of visible and ultraviolet light. To ease the handling of such pictures, that usually are taken in a large number of samples, they have been scanned by means of a hand scanner and stored in electronic data registers (digitalised). Meanwhile, today there are no methods or techniques available that make use of the pictures or the stored data to calculate (predict) properties of drill cores. The disadvantage concerning such photographing and hand scanning is that the digitalised pictures made by a hand scanner are not of an unlimited length, and they are usually present in one fixed format (scale). In addition, the quality of film and developing process vary because commonly a plurality of service companies are involved in the handling drill cores. Different companies have different types of cameras, film qualities and illumination conditions. In addition, the picture quality deteriorates in course of time. Reprinting (making new reports) will lead to reduced picture quality. Further, digitalisation of pictures in this manual manner will in addition be dependent of: Equipment (scanner type/resolution) Picture quality (positive or negative) The format of the picture (1 :5, 1 :4, 1 :2) The quality of a hand scanned digital picture is therefore unsatisfactory for image analysis and prediction of petro-physical parameters. In addition, hand scanning represents one additional and work consuming intermediate step. According to the present invention, there is provided a method and equipment that make it possible to predict petro-physical parameters of drill cores sampled while drilling for oil or gas, based upon digital image analysis. The method according to the present invention is characterised in that the images are recorded directly by means of a high resolution, digital camera that is moved along the drill core in equal intervals, as the drill core, while performing the records, is illuminated by a constant light at an angle (α) with respect to the surface of the drill core, while the digital recorded datas are transferred to a computer for further processing and storing. Further, the equipment is characterised in that it comprises a framework with a table for fastening the slabbed drill core, whereby there is arranged a movable digital camera above the table in conjunction with an upper part of the framework, said camera being adapted for movements along the drill core, sources of light for the constant radiation of light at an angle (α) with respect to the drill core, together with a computer for recording, processing and storing the digital data. The dependent claims 2 to 4 and 6 to 9 define advantageous features of the invention. Meanwhile, until present it has been regarded as impossible to make use of the implicit information according to the invention because of its enormous complexity if a method for quantifying should be based upon a deductive model for generating light/shadow pattern out of physical "first principles". The invention is based upon the inverted problem definition. As the light/shadow pattern is characterised empirically, that will say this complicated 2-dimensional pattern is transformed to other forms of simpler 1 -dimensional vectorial expressions being much easier to incorporate in statistical calibration techniques (PLS-multivariate calibration), it will now be possible to calibrate known petro-physical parameters from sand stones directly with these new implicit expressions. One central and critical factor of success for this composed method will be represented by a sequential application of traditional image analytic texture operators with new implemented methodology for characterising complex measuring sequences, AMT (Angle Measurement Technique). The AMT-method is described in the literature, but until present it has just been employed in geomorphologous works that differs totally from this new field of application, Formation Evaluation Workstation (FEW). The possibility of direct video image correlation and thereby Video based Petro-physical Parameter Predictor (VPPP) prediction facility of the FEW concept, is related directly to this innovative new combination of special illumination of the surface of the sand stone, texture derivation of the resulting light/shadow pattern, linearisation of the resulting texture image for AMT analysis, accompanied by a final empirical PLS multivariate calibration vis-a-vis laboratory measurements for the desired types of sand stone parameters. In the following, the invention shall further be described by example with references to the drawings where: Fig. 1 shows a recording rig according to the invention for digital core images in a frontal view, Fig. 2 shows the same in a side view. The recording rig according to the invention consists mainly as shown in Fig. 1 and 2 of a framework 1 with a table 2 for fastening a slabbed drill core 10, a movable position system 3, 4 including camera 9 and illumination 7, 8, together with an automatically control and operation system comprising a computer 6 and a control-/switch cabinet 5. The framework 1 may advantageously be made out of aluminium profiles, but its dimensions must be sufficient to secure a stable and vibration free function. The table 2 is fixed to the framework 1 and is, as previously mentioned, adapted to fasten a slabbed drill core 10 at a distance that is constant with respect to the camera 9. It should be dimensioned lengthways to handle drill cores at minimum 3 meters. The camera 9 is a high resolution digital video camera of the so called "frame capture" type and is arranged in a carriage 11 that is movably supported along a rail (not further shown) by means of a rail system (not shown either) in an upper frame part 3. The screw is driven by a step motor 4 that advantageously may have 200 steps in one revolution. If the screw is provided with a screw pitch of 5 millimetres per one revolution, this will give a movement ("linear resolution") of 0,025 millimetres per step. The carriage is, in addition to the camera, provided with two day-light lamps 8 and two armatures for ultraviolet light 7 adapted for illuminating the core sample while recording the images. The illuminating sources are thereby moved together with the camera as the images are recorded. In this manner, the illuminating conditions are held constant along the drill core. It should be pointed out that each and one of the light sources 8 and the light sources 7 is arranged and controlled in such a manner that the drill core may be illuminated symmetrically or non-symmetrically at different angles of incidence of the incoming light. When recording images that just have the purpose to show the drill cores, symmetrical illumination at an angle of 20-60° will be employed. Images recorded for use in statistical analysis, are taken by the use of asymmetric illumination where the angle of incidence is 5-30°, to achieve the best possible ligh shadow pattern while recording the images. All functions are controlled by means of a computer (the PC) 6 that is provided with a program for positioning the camera, calibration, recording functions, data storage and image splicing etc. All electric components, such as relays, fuses and electric junctions, between the PC and the hardware part of the equipment (motor and illumination) are arranged in the switch cabinet 5. The operation of the equipment is as follows; the carriage 11 together with the camera 9 and the illumination 7, 8 is moved along the rail in the above fixed frame part 3 in a stepwise manner, as the camera records one image a step of the drill core 11 fastened in the table 2 below. The camera, that may have a resolution up to 4400 x 3400 points, records the images digitally and transfers them electronically through the cable 12 to the PC 6. A self-developed software for the PC, that will not be further described here, handles and synchronises the control of the motor together with operation of camera and light. On the basis of the data that are recorded in this manner with respect to the position of the camera and the illumination conditions, the images of the drill core are put together (spliced) electronically to a long image that, per se, together with records of plural core samples may represent the geological structure for a complete well. The composed images are stored in the PC and may be distributed/given to users/customers on hard disc, magnetic tape or optical discs. In addition to the software for recording, processing and storing the digital images as mentioned above, it has been developed software for visualising images of drill cores on a data monitor, together with software for statistical analysis of digitalised images. The software for monitoring images is a self-developed program used to show 24-bits digital core images on a data monitor. The program may handle images of both TIFF- and BMP-format. The images may be spliced electronically and may be monitored as an unlimited, continuous image (for instance a complete well). Showing images in this manner is based upon a novel technique named segmented file-reading that is a method for fast visualising of digital images that extend beyond the place available on the data monitor. Segments of images are read from file to memory-buffers by means of background processing. This type of loading is controlled on basis of the user's latest movements in the image. The method implies that in approximately 90% of the cases there will be a sufficient amount of image segments in the memory to cover the part of the image that the user wants to see. This results in a substantial faster visualisation of the images compared to ordinary methods based upon reading of data directly from file. The program may in addition show data logs from file, depth correlated and scaled correctly, at the side of the digitalised image. The logs will be scaled automatically to the image as the image changes. The program may operate in 4 modus: 1 image + 3 logs 2 images + 2 logs 3 images Zooming of one image in scale 4:1 and 8:1 As concerns the software for statistical analysis, due to the application of small-angle, asymmetric illumination of the drill cores, there is now possible to obtain a light-/shadow pattern in the images that by means of the software may be employed to calculate/predict: - Averaged grain size and grain size distribution - Porosity - Permeability - Main mineralogy Quantification of the properties will depend upon the reflection of visible light and/or that there will be originated a light/shadow pattern in a diagnostic and quantifying manner.

Claims: Claims 1. Method for recording and processing of digital images of slabbed drill cores (10), characterised in that the images are recorded directly off the drill core (10) by means of a high resolution, digital camera (9) moved in equal intervals along the drill core (10), where the drill core is illuminated by constant light at an angle (α) with respect to the surface of the drill core when the records are taken, and where the digital recorded data are transferred to a computer (6) for further processing and storing. 2. Method according to claim 1 , charcterised in that the drill core is illuminated by the use of white and ultraviolet light. 3. Method according to claim 1 and 2, characterised in that the drill core is illuminated by an asymmetric illumination at an angle of incidence (α) between 20-60°. 4. Method according to claim 1 and 2, charactersed in that the drill core is illuminated by an asymmetric illumination at an angle of incidence (α) between 5-10°. 5. Equipment for recording and processing digital images of slabbed drill cores (10), characterised in that it comprises a framework (1) with a table (2) for fastening the slabbed drill core (10), whereby there is arranged a movable digital camera (9) above the table in conjunction with an upper part of the framework, said camera being adapted for movements along the drill core, sources of light (7, 8) for the constant radiation of light at an angle (α) with respect to the drill core, together with a computer (6) for automatic positioning of the camera, digitalisation, processing and storing of the digital data. 6. Equipment according to claim 5, characterised in that the light sources (7, 8) comprises sources radiating white light (daylight with Kelvin grade number > 3200) and ultraviolet light. 7. Equipment according to claim 5 and 6, characterised in that the light source(s) radiates light in one direction (α) for symmetric- and asymmetric illumination respectively. 8. Equipment according to claim 5 and 7, characterised in that the camera (9) and the light source(s) (7, 8) are arranged in a common carriage (11) that is adapted for movements along rails arranged in the upper part (3) of the framework. 9. Equipment according to claim 8, characterised in that the carriage is movable by means of a screw driven by a stepmotor (4), whereby said stepmotor is controlled by a computer.

Inventors: ELIASSEN OEYVIND, ESBENSEN KIM, OPGAARD HELGE, SCHEIE AASE, TJETLAND BJOERN GUNNAR, ELIASSEN, OEYVIND, ESBENSEN, KIM, OPGAARD, HELGE, SCHEIE, AASE, TJETLAND, BJOERN, GUNNAR
Applicants: ELIASSEN OEYVIND, ESBENSEN KIM, NORSK HYDRO AS, OPGAARD HELGE, SCHEIE AASE, TJETLAND BJOERN GUNNAR, ELIASSEN, OEYVIND, ESBENSEN, KIM, NORSK HYDRO A.S, OPGAARD, HELGE, SCHEIE, AASE, TJETLAND, BJOERN, GUNNAR
Application year: 1996
Main classification: G01N21
IPC codes: G01N15, G01N21