SAMPLING TOOL FOR OBTAINING SAMPLES OF FLUIDS PRESENT IN A WELL

Abstract: A sampling tool for immersing into a well for collection of samples of oil, gas or water during drilling for production of said fluids. The sampling tool (1) comprises a tubular, hollow and preferably cylindrical member with two chambers (12, 14) separated by a compressible pipe (9). Said sampling tool comprises an outer pipe (2) formed as a cylindrical member to withstand the reservoir pressure. Inside the outer pipe (2) is positioned a unit (13) forming a gas tight storage chamber (12) for the gas-/liquid samples and a chamber (14) for a counter pressure medium. The chamber (14) is formed by pressing the pipe (9) against the inside of a U-profile (10). During sampling, the volume of chamber (12) will increase and the volume of chamber (14) will be reduced corresponding to the increase of chamber (12). Total separation of the gas-/liquid sample from the counter pressure medium is obtained by applying a diffusion tight flexible pipe (9) and the gas-/liquid sample analyzed will thus be representative for the reservoir gas-/liquid sampled.

Description: Sampling tool for obtaining samples of fluids present in a well The invention relates to sampling tool immersed into a well for collection of samples during drilling for/production of oil, gas or water, comprising a tubular, hollow and prefer¬ ably cylindrical body. During the drilling operation and the production of hydrocar- bones it is necessary to collect samples of the gas/liquid present in the reservoir. This is obtained by immersing into the well a sampling tool for collecting samples at different depths. The sampler is then hoisted to the surface where the sample is transferred from the sampling tool to a suitable transportation bottle for further laboratory analysis of the chemical and physical characteristics of the sample. A sampling tool for obtaining gas-/liquid samples is basic¬ ally comprising a tubular cylindrical body comprising a stor¬ age chamber for conserving the gas-/liquid samples taken and valves for opening and closing the inlets to the chamber. In addition to the storage chamber the equipment also comprises various electronic equipment for measuring pressure, tempera¬ ture etc. The sampling tool is connected to the surface by a lifting wire having an insulated copper core. The sampling tool may also be mechanically controlled from the surface by using a mechanical steering rod inside the pipe. The steering rod is used to open and close the valves for the supply of gas-/liquid samples. Sampling tools with a storage chamber comprise usually a floating piston for separating the gas-/liquid sample physi¬ cally from a counter pressure medium. The counter pressure medium is used to control the flow from the reservoir into the storage chamber. During sampling the gas-/liquid samples flow into the chamber on one side of the piston and the counter pressure medium is pressed out of the cylinder into an atmospherical chamber. There are O-ring seals between the piston and the cylinder wall. These O-rings are exposed to wear caused by a combination of rubbing against the cylinder wall and contact with usually very aggressive hydrocarbon fluids. Besides, the seals allow diffusion from one side of the piston to the other. Therefore, the disadvantage of the present tool is that hydrocarbones leak or diffuse from one side of the piston into the counter pressure medium on the other side of the piston. When fractions of the gas-/liquid sample diffuse or leak from the sample due to worn-out piston seals, the gas-/liquid sample will not be representative and the test has to be repeated. This increases the costs for obtaining oil- and gas samples considerably, especially offshore because of very expensive rig time. Another method for sampling is to use tools with a time controlling system for opening the valves and a subsequent filling of the storage chamber. This method is not con¬ venient, because problems or delays often arises when the equipment is brought down into the well. Both the time cont¬ rolling system and the use of steering rod for opening the valves depend on relatively complex mechanical systems. The mechanical systems as described are exposed to wear and defects which will lead to increasing expenses both in form of broken equipment and needs for repeating the tests. The main object of the present invention is to develop a method for obtaining representative gas-/liquid samples without risk of leakage from the storage chamber to the counter pressure chamber. It is further an object to provide an apparatus which is reliable and easy to handle and give a quick and reliable sampling. These and other objects of the invention are obtained with the apparatus described below, and the invention is further defined and characterized in the accompanying claims. Since the problem with the known equipment was both related to the piston rings and a complicated mechanical construction it was essential to replace the O-rings with another form of seal or membrane and generally to simplify the construction of the sampling tool. Because O-rings or seals are needed in all piston/cylinder constructions one had to find an arrange¬ ment without pistons which also could separate the counter pressure medium from the gas-/liquid sample. After the inven¬ tors had considered different solutions they tried to use a membrane formed as a pipe for separating the sample from the counter pressure medium. The arrangement was tested, and cer¬ tain types of membranes provided a solid and diffusion tight seal. If a flexible membrane made of a diffusion tight mate¬ rial was used, the danger of leakage from the storage chamber into the chamber containing the counter pressure medium was eliminated. The sampling tool according to the invention comprises mainly a cylindrical body with two channels and valves basically positioned at each end of the said body. One channel is leading to the chamber for counter pressure medium and the other channel to the gas-/liquid storage chamber. The chamber for the counter pressure medium is limited by the inner wall of an outer pipe and an outer wall of a pipe inside the other. The internal pipe is made of flexible material, pre¬ ferably lead. The storage chamber is limited by the inner wall of the lead pipe and two supporting wedges fixed to a U-profile. The U- profile and the unit of the lead pipe and the wedges form a gas-tight chamber inside the lead pipe. Before the apparatus is immersed into the well for sampling, the chamber between the outer pipe and the inner pipe is filled with a counter pressure medium, for instance glycol, and the flexible pipe is folded around the U-profile and the wedges. Air and other possible polluting gases/fluids are thus pressed out of the sampling chamber. The sampling tool is then immersed into the well to a given sampling depth. The valve for the gas-/liquid supply channel is opened simul¬ taneously as the valve for discharging the counter pressure medium is opened either to a chamber with atmospherical pressure or directly to the reservoir formation surrounding the sampling unit. The gas-/liquid sample will fill the storage chamber inside the lead pipe. This pipe is now gradu¬ ally forced back to its original cylindrical shape as the chamber is filled by the gas-/liquid sample. Simultaneously, the volume of the counter pressure chamber is reduced and the counter pressure medium is gradually forced into the chamber at atmospheric pressure. The sampling velocity is regulated by regulating the flow of counter pressure medium through a nozzle. The chamber at atmospheric pressure has a volume less than the volume of the storage chamber. That means that at maximum filling of the storage chamber there will be some liquid remaining in the counter pressure chamber. The object of the volume difference of the two chambers is to prevent the lead pipe having metal to metal contact and being punctured. When the sampling is done, the sampling unit is raised to the surface by a lifting wire. The gas-/liquid samples are then transferred at a constant pressure and volume to suitable transport and storage bottles for further transport and analysis. Other characteristics of the invention are described in detail with reference to the accompanying drawings 1-4 in which, Fig. 1 illustrates the sampling tool according to the invention Fig. 2 a,b,c illustrates the sampling tool in cross sec¬ tional view A-A, B-B and C-C Fig. 3 illustrates the sampling tools connected and where one of the samplers are illustrated in longitudinal section. Fig 1. shows the sampling tool 1 comprising two chambers 12,14 mainly separated by a compressible pipe 9. The sampling tool 1 consits of an outer pipe 2 in the form of a cylindri- cally shaped container for retaining the reservoir pressure. Inside the outer pipe 2 there is a unit 13 forming a gas tight chamber 12 for the gas-/liquid sample. The dotted line 15 illustrates this unit when the pipe 9 is compressed. The chamber 14 is limited by the inside of the outer pipe 2 and the outside of the compressed pipe 9. The inner unit 13 con¬ sists of wedges 5 and 6, an U-profile 10 and the pipe 9 preferably made of lead. The pipe 9 can be made of other suitable materials. The essential thing is that the material is flexible and diffusion tight. For a less flexible metal than lead, it is important for the compression that the pipe has a weakened field from where compression can start. If flexible material such as rubber is used there will be no need for a weakened field. Generally, it is the type of samples that determine what material to choose in the com¬ pressible pipe. The supporting wedges 5 and 6 are mounted and secured to each end of the U-profile. The U-profile and the wedges 5 and 6 form one unit which is positioned inside the lead pipe 6. The lead pipe 6 is fastened to the wedges 5 and 6 for instance by glue or solering and are then forming a gas tight unit with a chamber 12 for the gas-/liquid sample. The wedge 6 has a central longitudinal bore 8 ending inside the lead pipe 9. This bore 8 is for supply of the gas-/liquid sample the storage or conservation chamber 12. The chamber 14 is filled with a counter pressure medium before the gas- liquid sampling starts. This gives a controlled and gradual filling of chamber 12. The wedges 5 and 6 are in one end circular and in the other end slanted. During filling of chamber 14 the slanted ends of the supporting wedges give a smooth transition from circular shape of the lead pipe to the compressed state. Fig. 2 shows the sampling tool in cross sectional view A,B and C. In section A-A the lead pipe 9 and the supporting wedge 5 and 6 are circular. This part of the lead pipe will remain unchanged during filling of both chambers 12 and 14. The cross section of the unit 13 is somewhat less than the inner cross section of the outer pipe 2. The gap between the inside of pipe 2 and the outside of pipe 9 will always be filled by some counter pressure medium and thus reduce the wear of the lead pipe. The gap also simplifies the insertion of the unit 13 and allow a flow of the counter pressure medium during filling of chamber 14. Cross sectional view B-B shows the shape of the lead pipe when the chamber 12 for the gas-/liquid sample is filled. The lead pipe 9 will have the original pipe shape in this position. The gas-/liquid sample in chamber 12 has during filling reduced the volume of chamber 14 significantly and pressed the counter pressure medium into a separate atmospheric chamber (not shown) . Cross sectional view C-C shows a sampling unit where the lead pipe is pressed against the inside of the U-profile 10, as shown by the dotted line 15 in Fig. 1. This is the shape of the lead pipe when the sampling tool is ready to for use and filled with a counter pressure fluid such as glycol. The counter pressure fluid flows during filling on the outside of the lead pipe 9 and press the lead pipe 9 against the inner wall of the U-profile and thus reduces the volume of the storage chamber 12 approx. to zero. When the collection of the gas-/oil sample starts, the chan¬ nels leading to the reservoir are opened simultaneously as the channel to the chamber at atmospheric pressure is opened. The gas-/liquid sample flows due to the reservoir pressure into the inside of the lead pipe resulting in that the coun¬ ter pressure medium on the other side of the lead pipe is pressed into the atmospheric chamber. The gas-/liquid sample and the counter pressure medium is because of the lead memb¬ rane completely separated during sampling. The counter pres¬ sure medium cause a smooth filling of the storage chamber 12 and do not cause unnecessary strain on the lead pipe. The atmospheric chamber for the counter pressure medium has less volume than the storage chamber. Some of the counter pressure medium will therefore remain on the outside of the lead pipe and prevent the lead pipe from metal to metal contact or being punctured. Fig. 3 shows a complete sampling system including the valves 3,4 for control of the sampling operation. The outer pipe 2 has threads 18 in both ends for connection to the valve system 3,4. The supporting wedges 5 and 6 are not identical. One of the supporting wedges, in this example wedge 6, has a male part 7 for connection with the female part of the valve system. The valve system can in addition to regulating the opening/closing of the channels also function as a connection section for a second sampling tool 16,17. The lead pipe including wedges and U-profile is finished in the workshop where it is pressure- and diffusion tested before it is mounted as one unit in the outer casing. By applying a sampler according to the invention, one has obtained a sampling tool where the gas-/liquid sample are separated from the counter pressure medium. There are no possibility for any leakages or diffusion from the storage chamber into the counter pressure chamber. The storage cham¬ ber according to the invention is simple to manufacture and use, and there are no parts exposed to wear. The sampler is therefore cheap to manufacture and most reliable.

Claims: Claims 1. Sampling tool (1) for immersing into a well for col¬ lection of samples during drilling for/production of oil, gas or water, comprising a tubular, hollow and preferably cylindrical member (2) c h a r a c t e r i z e d i n t h a t inside the cylindrical member (2) it is positioned a collapsible tubular unit (9) for separating a chamber (14) for a counter pressure medium from a chamber (12) for a gas-/liquid sample. 2. Sampling tool according to claim 1, c h a r a c t e r i z e d i n t h a t the unit (9) at both ends have fixed supporting wedges (5) and (6) for limiting the inner chamber (12) for the gas-/liquid sample. 3. Sampling tool according to claim 1, c h a r a c t e r i z e d i n t h a t the supporting wedges (5 and 6) are fastened to both ends of a U-profile (10) and forms one unit with said U-profile (10) . 4. Sampling tool according to claim 1, c h a r a c t e r i z e d i n t h a t the unit (9) and the unit comprising the supporting wedges (5 and 6) and the U-profile are interchange¬ able. 5. Sampling tool according to claim 1, c h a r a c t e r i z e d i n t h a t the supporting wedges (5 and 6) and the U-profile (10) are rounded at all corners which are not in permanent contact with the unit (9) . 6. Sampling tool according to claim 1, c h a r a c t e r i z e d i n t h a t the unit (9) is made of a compressible tubular mate¬ rial, preferably lead.

Inventors: BOEE EINAR, BOEE, EINAR
Applicants: NORSK HYDRO AS, NORSK HYDRO A.S
Application year: 1990
Main classification: E21B49
IPC codes: E21B49