GB2121084A - Well testing apparatus - Google Patents

Abstract

A wireline testing tool of oil and gas wells comprises a substantially hollow body 2 to be received within the bore of a drill stem 1, containing instruments 8 for testing the well fluids. The body 2 is provided with upper outlet ports 4 and lower inlet ports 13 to allow passage of well fluids into the body 2 and into direct communication with the instruments 8. The upper ports 4 may be closed to provide shut-in of the well by sliding an outer member 3 over the outlet ports 4. <IMAGE>

Description

SPECIFICATION Well testing apparatus This invention relates to apparatus for testing oil or gas exploration wells.

In the evaluation of an oil or gas exploration well one of the principal parts of the data acquisition is the drill stem test (DST). The DST is the production of the reservoir fluid under carefully controlled conditions to provide information on the possible future performance of a production well at the exploration site. In the DST, the column of the drill pipe is used as the temporary production tubing.

During the drilling of any well formation fluids are prevented from entering the well, under their own pressure by the weight of the column of drilling mud in the well. To enable test production of fluids from a selected formation through the drill pipe in a safe manner the column of mud must remain intact around the drill pipe.

An inflatable packer run, as part of the drill pipe column, provides sealing between the drill pipe and the side wall of the well which may be bare rock or steel casing. To enable production the drill pipe must contain a fluid which is both of lower density than the mud and gives hydrostatic head pressure which is less than the formation pressure.

The most useful data available from the DST are pressures relating to the flowing well, and most importantly, measurements of the build-up of reservoir pressure when the well is closed in and the reservoir is stabilising. The latter data gives the most direct information on the permeability of the reservoir rock and the degree of damage to permeability in the immediate vicinity of the well.

In order to provide a basis for sound interpretation the pressure measurements must be of great accuracy and the well must be able to be shut-in down hole to prevent production of fluids into the well bore or settling out of fluids after a surface shut in. The movement of fluids in the long vertical well bore after shut-in will cause a pressure transient that would obscure the reservoir effects that are of interest.

Hitherto conventional drill stem testing uses a packer run which is placed in a point fairly near to the bottom of the drill string. A downhole shut-in valve is placed near to but above this. Clockwork driven recorders on Bourdon Tube type gauges are placed in protected holders below the shut-in valve to 'see' the reservoir flowing and shut-in pressures. A similar clockwork driven recording thermometer provides temperature data. This was the state of the art about four years ago.

This system had the following problems:- a) Inaccurate and insensitive gauges meant that long tests were required to provide data that could be interpreted with any reliability.

b) The engineer conducting the test had no knowledge of the situation down hole or whether the gauges were even working.

c) The gauges were run in the DST down hole equipment being subjected to very rough handling during the run-in of drill pipe.

With the advent of electrically operated pressure gauges the possibility of very much improved accuracy was offered. However, there was one very major drawback the gauge had to be run on conductor wire-line and therefore could not pass through the down hole shut-in valve which would obviously cut the wire. One alternative, recently available, is an electrical gauge with a self contained recording device. This is designed such that it can be run in a conventional gauge holder.

This system has the serious disadvantage of not providing the engineer with information as the test proceeds requiring the engineer to act blindly not knowing exactly what is happening down hole.

On production wells where down-hole shut-ins are not normally possible, wire-line electrically operated gauges are run routinely. This requires the careful monitoring of after flow well bore effects so that this data can be ignored and only reservoir effects considered. This has major time disadvantages in low productivity gas wells and oil wells where after flow effects are very prolonged and tests have to be extended.

The most recent development which makes electrical gauges a practical tool in DST's is the 'SPRO' system developed by Flopetrol/Dowell Schlumberger. This system uses a gauge built into the down hole shut-in valve. The gauge is so arranged as to give pressure measurements beneath the valve by providing a pressure communication to the gauge mounted above the shut-in device.

The gauge and shut-in assembly is run in as part of the drill pipe column and the wireline electrical connection is made after the gauge and valve assembly is in position. This has the following disadvantages: a) An elaborate shut-in valve assembly run as part of the drill pipe column requiring the presence at the test of a specialist downhole engineer. This together with the tool itself can prove very expensive.

b) The gauge electrical cbnnection has to be made in the presence of well bore fluids and is not altogether reliable.

c) The flow through the valve is restricted by a rather narrow path approximately 2.00 cm diameter.

The present invention proposes well testing apparatus which seeks to avoid the disadvantages associated with both wireline apparatus and specially adapted pipe runs.

According to the present invention there is provided apparatus for the testing of wells said apparatus being in the form of an assembly adapted to be received within the bore of a pipe drill run and arranged to carry instruments for data acquisition characterised in that the assembly comprises a pair of concentrically arranged hollow members, the inner member being provided with longitudinally spaced inlet and outlet ports to allow passage of fluids from the well through the inlet ports into the lower end of the inner member and the outer member being arranged to slide over the upper part of the inner member thereby to close the upper outlet ports and wherein means are provided for actuating the outer slide and for sealing the annular space between the inner member and the wall of the pipe run in the region between the inlet and outlet ports, said instruments being located within the inner member and being in communication with fluid in the region between the inlet and outlet ports.

The invention will be described with reference to the accompanying drawings which is a diagrammatic sectional elevation of the apparatus in accordance with the invention.

Referring to the drawing, the assembly, located within the bore of drill pipe 1 comprises an inner body 2 and an outer sleeve 3. The body 2 is provided with ports 4 which may be in the form of elongate slots in the wall thereof. A septum 5 divides the body into upper and lower chambers 6 and 7 respectively. Chamber 7 is provided with inlet ports 1 3 at the lower end to receive the well fluids and within this chamber are located the instrument packages, indicated generally at 8, e.g.

thermometer, pressure measuring devices and flowmeters. Cables from the instruments run to the surface through the hermetically sealed conduit 9.

The outer sleeve 3 is connected to a ram and piston 10 which moves within chamber 6. The piston is actuated pneumatically by gas under pressure into the upper part (11) of chamber 6. A gas reservoir and gas control valves (not shown) are provided in the upper part of chamber 6 and these may be remotely operated via cables from the surface running through conduit 9. Upon release of the pneumatic pressure in chamber 11, the sleeve, piston and ram assembly are urged upwardly by the action of return spring 12.

In order to seal the annular space between the body 2 and the wall of pipe 1 an inflatable packer 14 is provided in the region between the ports 4 and the lower open end of chamber 7. The packer may be inflated pneumatically (means not shown).

The DST tool in accordance with the invention may be run into the well bore by one of alternative sequence of operations. Firstly a conventional down hole shut in valve, in the shut mode, may be run in as part of the drill string and, after the DST tool is lowered into the hole down the hollow drill stem. Upon opening of the lower down hole shutin valve, flow control is regulated by the valve assembly of the tool. An alternative method of locating the tool is to run in a drill string and to run in an open ended drill string down the hole. The column of mud in the drill stem is replaced with a less dense fluid such as sea water, diesel oil or nitrogen and thence the DST tool is sunk through the less dense fluid. After set in, the fluid control is again regulated by the valve assembly of the tool.

The use of the testing tool in accordance with the invention has many technical advantages. An example is the selective perforation of intervals between tests to evaluate the performance of short intervals of the reservoir thickness and their aggregate. Down-hole flowmeters can be run to measure the flow from each group of perforations.

The present invention may be used with advantage for testing producing wells. Whilst this may not be so important for high rate oil and gas wells, in poorer wells particularly with two phase flow, redistribution of the well bore contents after shut-in and after flow into a large capacity well can obscure valuable data. In order to provide this facility with existing equipment was necessary to provide a special nipple which is an integral part of the tubing string and must run in when the well is completed. Thus existing wells which do not have a modified tubing string cannot be tested with the existing equipment. In contrast no modifications to the production tubing are required for use of the present invention and it may be used on pre-existing wells.

Since in accordance with the invention, the testing instruments are not run in with the drill string, there is little risk of damage, as would be in the case of known DST tools since they are subject to jarring as the drill string is run in.

Furthermore since the measuring instruments are in direct communication with the well fluids under test, anomalies such as temperature changes and slow pressure changes on shut-in are eliminated. Thus results are available both quickly and accurately, saving in both time and costs.

Claims (3)

1. Apparatus for the testing of wells, in the form of an assembly adapted to be received within the bore of a pipe drill run and arranged to carry instruments for data acquisition, characterised in that the assembly comprises a pair of concentrically arranged hollow members, the inner member being provided with longitudinally spaced inlet and outlet ports to allow passage of fluids from the well upwardly through the inlet ports into the lower end of the inner member and the outer member being arranged to slide over the upper part of the inner member thereby to close the outlet ports, and wherein means are provided for actuating the outer sliding member and for sealing the annular space between the lower end of the inner member and the wall of the pipe run in the region between the inlet and outlet ports and said instruments are located within the inner member and being in direct communication with fluid in the region between the inlet and outlet ports.

2. Apparatus as claimed in Claim 1 wherein said sealing means is an inflatable packer.

3. Apparatus as claimed in Claim 1 or Claim 2 wherein said outer slide member is pneumatically actuated.