Method of conducting in situ measurements of properties of a reservoir fluid

#The invention regards a method of conducting in situ measurements of properties of reservoir fluids by means of measuring instruments/apparatuses enclosed in a casing connected to the outer, free end of a string of tubulars in a wellbore/well that extends at least down to the hydrocarbon-containing layer of the reservoir, where the inherent pressure of the reservoir fluid (the reservoir pressure) ensures the inflow of reservoir fluid to the instrument/apparatus casing through an inlet or possibly a combined inlet/outlet, and where signals that are generated via electronics etc. on the basis of measurement results obtained in situ, are transmitted further to the surface position, possibly for further analysis.

#The use of new technology for, among other things, drilling and production in ground formations with high temperatures and pressures, the injection of water and gas to increase the degree of recovery, multiphase production on the seabed and transport of produced hydrocarbons through seabed pipelines place increasingly stringent demands on the exactitude of the knowledge that is required of the physical and chemical properties of the gas, oil and water to be produced from the deposit. Previously, such knowledge of the reservoir fluid in the ground formation was normally obtained through full production testing. Today however, there is a definite tendency towards an increased use, of various sampling tools that may be run into and out of the well during drilling, by means of a wire string. However this last method allows fewer possibilities for obtaining data regarding relevant reservoir fluid parameters than that which is possible with full production testing.

#The above methods each have different advantages and disadvantages. The strong point of full production testing is that data may be collected from a large volume of reservoir fluid, ensuring highly reliable data. The main weak point is the great costs incurred, for instance when hiring a rig and other necessary equipment. Another significant disadvantage is that it will be necessary somehow to handle the large volume of reservoir fluid that is transported up to the surface. At present, this is normally done by burning the oil and gas, which is damaging to the environment. Consequently, the oil companies aim to cease such burning after 2003. Essential advantages of the use of sampling and measuring equipment that is lowered into the well by a wire string, is that it allows continuous sampling of the reservoir fluid during drilling, and that it may be carried out at a considerably lower cost than full production testing. In addition, there is no need to burn oil and gas. As already mentioned, the main weak point of the equipment is the limitations on what the equipment can provide in the way of data regarding relevant reservoir fluid parameters. As an example, it is not possible to obtain essential data regarding the flow conditions in the reservoir fluid. Also, the equipment can not be used in connection with saturated gas reservoirs, as the pressure and temperature can not be stabilised. This weakness is further enhanced in consequence of very small volumes of reservoir fluid being extracted, and of the equipment having to be manipulated from the surface. The latter fact may in addition lead to the measurement results for the reservoir fluid becoming unreliable. Such errors in the measurement results may among other things be due to the equipment not being positioned correctly in the reservoir during sampling, to the reservoir fluid at the sampling location having been contaminated by the drill fluid used during drilling, and to sand that follows the reservoir fluid upon sampling causing cracks and leakage in the equipment.

#A more detailed account of a preferred embodiment of the invention will be given with reference to the appended drawings, in which:

#FIG. 1 shows a schematic cutout in the lower part of an exploration well being drilled in a ground formation;

#FIG. 2 is a large-scale detail drawing, partly with a section through the tubular string, and in which the piston movably arranged in the bore of this, and stationary seat for same, may be seen.

#The well is drilled by means of drilling equipment comprising a drill bit 15 with an associated drill string 4, the in situ sampling, and flow and volume measurements or the other analyses in the reservoir fluid being carried out by use of equipment provided inside an associated casing 7 that encloses the drill string above the drill bit 15. The well is sealed off in an area by the hydrocarbon-containing layer 2 of the formation by means of packings 5, 6 that are arranged externally on the casing 7 and have expanded to abut the wall of the borehole in a sealing manner. Some parts of the casing have been omitted, so that certain components of the equipment for sampling, flow and volume measurements or other analyses can be indicatively outlined in the figure.

#In the embodiment of the invention, it is adapted to use in in situ sampling, flow and volume measurements, and any other analysis in reservoir fluid that is encountered in a ground formation 1 during drilling of an exploration well 3 for hydrocarbons but there is obviously nothing to prevent the present invention from being used in a different context, e.g. in a ground formation that has already been put into full production. As mentioned above, the aim is, among other things, for typical properties or parameters of the reservoir fluid that is encountered in the ground formation 1 to be determined with the greatest possible degree of accuracy, without a large volume of hydrocarbons having to be brought out of the well 3 and up to the surface. Thus the well 3 is sealed off in an area immediately above and below (by 5 and 6) the hydrocarbon-containing layer 2 of the ground formation 1. Then reservoir fluid from the hydrocarbon-containing layer 2 is introduced to a drill string 4 that has at least been passed through the sealed-off area of the well 3. The sampling, the flow and volume measurements and the other analyses in the reservoir fluid are conducted in the sealed-off area of the well 3. Preferably this will only take place when the drill string 4 has been closed off and filled with incoming reservoir fluid. With that, the sampling and respective measurements or analyses are only conducted after a large volume of reservoir fluid has been introduced into the drill string 4. This allows samples or measurements to be taken in a reservoir fluid that has stabilised after drilling, and which essentially contains no drill fluid. This as a consequence of, among other things, the previously mentioned piston 17 separating the reservoir fluid RV in chamber 19 below the piston 17 from the above water or N2.

#Said water or N2 may in an initial position or in a transitional position be pressurised in order to force drilling mud/fluid from the drill string/production string 4 and out into the annulus 3. Following perforation, the piston 17 will travel upward (arrow A) into the string 4 as reservoir fluid RV is admitted into the drilling section 19 located below the piston 17 and expands as the piston 17 is moved up. After the sampling and respective measurements have been completed through use of the sampling, measuring or analysis equipment 9-12 that has been introduced into the well 3 together with the drill string 4, the reservoir fluid from the drill string 4 is returned to the hydrocarbon-containing layer 2 of the ground formation 1 in a suitable manner. Then the sampling, measuring or analysis equipment 912 is withdrawn from the well 3 along with the drill string 4, in order to allow the small amount of reservoir fluid that comes up to the surface with it to be examined more closely in the laboratory. This avoids a large volume of reservoir fluid having to be carried to the surface, as mentioned previously.