NO320901B1 - Method and apparatus for formation testing with fluid transfer between two formation zones - Google Patents

Description

BACKGROUND OF THE INVENTION

Field of the Invention - This invention relates to the testing of underground formations or reservoirs. More specifically, this invention relates to a method and an apparatus for isolating a downhole reservoir as well as testing the reservoir formation and reservoir fluid.

Background information - When drilling a well for the commercial exploitation of hydrocarbon reservoirs, numerous underground reservoirs and formations will be encountered. In order to derive information about these formations, such as whether the reservoirs contain hydrocarbons, logging devices have been installed on drill strings to evaluate several characteristics of the reservoirs in question. Equipment for measurement during drilling (hereafter referred to as MWD) has been developed and contains devices for logging resistivity and core technical data and which can continuously monitor certain of these features while drilling takes place. These MWD equipment can generate data that includes hydrocarbon presence, saturation levels and porosity data. Furthermore, telemetry equipment has been developed for use with the MWD devices to transmit the relevant data to the earth's surface. A common telemetry method is the sludge pulse method, and an example of this can be found in US patent no. 4,733,233. An advantage of MWD equipment is that analysis of underground reservoirs is performed in real time for further commercial exploitation.

Commercial development of hydrocarbon fields requires considerable amounts of capital. Before field development begins, operators want to have as much data as possible available to be able to evaluate the reservoir in question for commercial exploitability. Despite advances in data acquisition during drilling, using MWD equipment, it has often been necessary to carry out further testing of the hydrocarbon reservoirs in order to derive additional data. After the well has been drilled, the hydrocarbon zones are therefore often tested again using other equipment.

One type of post-drilling testing involves draining fluid from the reservoir, collecting samples, shutting in the well so that the pressure is allowed to build up to a static level. This sequence can be repeated several times on several different reservoirs within a given well bore. Testing of this type is known as a pressure build-up test. One of the important aspects of the data collected during such a test is the pressure build-up information collected after

the pressure is drawn down. Based on this data, information can be derived with regard to the reservoir's permeability and size. Furthermore, actual samples of the reservoir fluid must be taken, and these samples must be examined to collect relevant data regarding pressure, volume and temperature and which are important for estimating the reservoir's hydrocarbon distribution.

In order to be able to carry out these important tests, it is constantly necessary to withdraw the drill string from the borehole. The various tools designed for such testing are then introduced into the borehole. A wire cable is often used to lower the test tool into the borehole. This test tool often uses gaskets to isolate the reservoir. Numerous communication devices have been designed to be able to handle the sample assembly, or alternatively to be able to transfer data from the sample equipment. Certain of these constructions include means for signaling from the earth's surface by means of pressure pulses through the fluid in the borehole, and then to or from a downhole microprocessor arranged inside or in connection with the sample assembly. Alternatively, a lead cable can be lowered from the earth's surface into a receiving landing site located inside a sample assembly, thereby creating electrical signal communication between the surface and this sample assembly. Regardless of the type of test equipment that is currently used, and regardless of the type of communication equipment that is used, the time and costs required to pull out the drill string and lead a second test rig into the hole will be of significant importance. If the hole is also highly deviated, a lead cable cannot be used to perform the test either, as the test tool will not possibly be able to penetrate deep enough into the hole to reach the desired formation.

There is also another type of problem, which is related to the pressure conditions down in the borehole and which can occur during drilling. The density of the drilling fluid is calculated to achieve maximum drilling efficiency while maintaining a certain safety, and the density will then depend on the desired relationship between the weight of the drilling mud column and the downhole pressure that will be encountered. As different formations will be penetrated during the drilling, the downhole pressure will be able to change significantly. With the equipment currently available, there is no possibility of accurately sensing the formation pressure as the drill bit penetrates the formation. The formation pressure may then be lower than expected, which will allow the mud density to be lowered, or the formation pressure may be higher than expected, which may possibly result in a pressure backlash. As this information is not readily available to the drilling operator, it may consequently happen that the drilling mud can be maintained at too high or too low a density for maximum efficiency and greatest possible safety.

WO 96/30628 entitled "Formation Isolation and testing Apparatus and Method" describes an apparatus and method for obtaining samples of pristine formation fluid using a work string designed to carry out other tasks downhole such as drilling, maintenance operations and resumption operations. An expandable element extends against the formation wall to obtain the pristine fluid sample. But the test tool is in the standby position, the expandable element is retracted into the work string protected by another structure from being destroyed during the work string's operation. The device is used to investigate downhole conditions while a work string is being used and the measurements can be used to adjust the properties of the working fluids without the work string having to be pulled out of the borehole. When the expandable element is a gasket, the device can be used to prevent a blow from reaching the surface, adjust the density of the drilling fluid and then continue using the work string.

There is therefore a need for a method and an apparatus which will enable pressure testing and fluid penetration testing of potential hydrocarbon reservoirs as soon as the borehole has been drilled into the reservoir, without removal of the drill string. Furthermore, there is a need for a method and an apparatus that will enable adjustment of the drilling fluid's density in response to changes in downhole pressure, thereby achieving the greatest possible drilling efficiency. Finally, there is a need for a method and an apparatus which will make it possible to prevent blowout down the borehole, thereby promoting drilling safety.

BRIEF SUMMARY OF THE INVENTION

A formation testing method and testing apparatus will be described. This test apparatus is mounted on a work string for use in a borehole filled with fluid. It may be a work string designed for drilling, re-entry work or overhaul applications. As will be required for many of these applications, the drill string should be able to penetrate highly deviated boreholes, including horizontally or even upwards. Therefore, in order to be maximally useful in achieving the purposes of the present invention, the working string must be such a string that is capable of being forced into the hole, rather than simply being able to fall down like a wire cable. The work string may contain equipment for measurement during drilling as well as a drill bit or other drive elements. The formation test apparatus may comprise at least one expandable packing or other expandable structure which can expand or extend into contact with the wall of the borehole, means for movement of fluid, such as a pump, to thereby be able to take in formation fluid, a non-rotating sleeve, a extendable stabilizer vane, a core withdrawal device, as well as at least one sensor to measure a characteristic property of the fluid. This test apparatus will also contain regulating means to control the various valves or pumps used to regulate the fluid flow. The sensors and other instruments as well as the regulation equipment must be carried by the tool. This tool must have communication equipment capable of communicating with the earth's surface, and data can then be telemetered to the surface or stored in a downhole data storage for later recovery.

The procedure includes drilling or re-entering a drilled hole as well as selecting a suitable underground reservoir. The pressure or another parameter of the fluid in the borehole at the reservoir, the bedrock, or both, can then be measured. The expandable element, such as a packing or a test probe, is placed against the borehole wall to isolate a portion of the borehole or at least a section of the borehole wall. In an embodiment with a non-rotating sleeve, the drill string can continue to rotate and be driven forward while the sleeve is kept stationary during execution of the test.

If two packing devices are used, this will form an upper annulus, a lower annulus and a middle annulus inside the borehole. The middle annulus corresponds to the isolated part of the borehole, and is then positioned on the reservoir to be tested. The pressure, or another property, is then measured inside the intermediate annulus. The well drilling fluid, which primarily consists of drilling mud, can then be extracted from the intermediate annulus with the help of the pump. The level at which the pressure inside the intermediate annulus stabilizes can then be measured, and this will then correspond to the formation pressure. Pressure can also be applied to fracture the formation, or to perform a pressure test on it. Additional expandable elements can also be provided to isolate two or more permeable zones. This then allows the pumping out of fluid from one or more of the zones to one or more of the other zones.

Alternatively, a piston or other sample probe may be extended from the sample apparatus for sealed contact with the weight of the borehole, or another expandable element may be expanded to produce a zone from which substantially pristine formation fluid may be withdrawn. This could also have been achieved by extending a locating arm or stabilization rib from one side of the test tool, thereby bringing the opposite side of the test tool into contact with the wall of the borehole, so that a sampling port for the formation fluid is thereby released. Regardless of the apparatus used, the purpose is to create a zone of untouched formation fluid, from which a fluid sample or core sample can be taken, or in which the fluid's properties can be measured. This can be achieved in different ways. The first-mentioned example above involves using inflatable packings to isolate a part of the entire extent of the borehole, and then extracting drilling fluid from the isolated area until it is filled with formation fluid. According to the other examples given, the purpose is achieved by extending an element towards a place on the wall of the borehole, so that the formation is thereby directly contacted and drilling fluid is extracted.

Regardless of which device is used, it must be designed so that it is protected during the performance of the most important work operations for which the work string is intended, such as drilling, reintroduction or overhaul. If an extendable probe is used, this can be retracted into the tool, or it can be protected by means of adjacent stabilizers, or both of these methods can be used. A gasket or other expandable elastomeric element may be retracted into a recess in the tool, or it may be protected by a sleeve or other type of cover.

In addition to the pressure sensor mentioned above, the formation test apparatus can contain a resistivity sensor to measure the resistivity of the wellbore fluid and the formation fluid, or possibly other sensor types. The resistivity of the drilling fluid can be significantly different from the resistivity of the formation fluid. If two packings are used, the resistivity of the fluid pumped out from the intermediate annulus can be monitored to determine when all the drilling fluid has been withdrawn from the intermediate annulus. As flow is supplied from the isolated information into the interannular space, the resistivity of the fluid pumped out from the interannular space can be monitored. As soon as the resistivity of the extracted fluid deviates sufficiently from the resistivity of the drilling fluid, it is assumed that formation fluid has then filled the intermediate annulus, and that the outflow has ended. This can also be used to verify correct sealing for the seals, as leakage of drilling fluid past the seals will tend to maintain the resistivity at the same level as the resistivity value of the drilling fluid. Other types of sensors that can be included are devices for measuring flow, viscosity sensors, density measuring devices, devices for measuring electricity values, and optical spectroscopes.

After confining the formation, the pressure in the intermediate annulus can be monitored. Pumping can also be initiated to extract formation fluid from the intermediate annulus with a measured flow rate. Pumping of formation fluid and measurement of pressure can be performed in sequence and as desired to produce data that can be used to calculate various properties of the formation, such as its permeability and size. If direct contact with the wall of the borehole is used, rather than isolating a section of the borehole, similar tests can be carried out by arranging test chambers inside the test apparatus. These test chambers can be maintained at atmospheric pressure while the work string is brought to drilling or lowered into the borehole. Once the extendable element has been placed in contact with the formation, and such that a sample port is opened for formation fluid, a selected sample chamber can be brought into fluid communication with the sample port. As the formation fluid will have a much higher pressure than atmospheric pressure, formation fluid will flow into the test chamber. In this way, several test chambers can be used to carry out different pressure tests or to take fluid random samples.

In certain embodiments using expandable packings, the formation test apparatus incorporates a return flow passage for the drilling fluid for the purpose of allowing the return flow of drilling fluid from the lower annulus to the upper annulus. It also includes at least one pump, which can be a Venturi pump or a pump of another suitable type to prevent overpressurization in an intermediate annulus. Overpressurization may be undesirable due to possible loss of packing seals, or because it may inhibit the working function of expandable elements which may be driven by the pressure difference between the inner bore of the working string and the annulus, or by a fluid pump. To prevent overpressurization, drilling fluid is pumped down through the longitudinal internal bore in the drill string past the lower end of the work string (where the drill bit is usually located) and up to the annulus. When fluid is channeled through the return flow passage and the Venturi pump, so that a low pressure zone is created at the Venturi and the fluid inside the intermediate annulus is kept at a lower pressure than the fluid in the return flow passage.

The device can also comprise a circulation valve to open and close the internal bore in the working string. A parallel valve can be placed in the work string and be operationally coordinated with the circulation valve to thereby enable flow from the work string's internal unbore to the annulus around the work string when the circulation valve is turned off. These valves can be used when operating the test apparatus as a downhole blowout barrier.

In the case where an inflow of the reservoir fluid invades the borehole, which is sometimes called a "well kick", the method can include process steps that involve setting the expandable gaskets, and then setting the position of the circulation valve in the closed position. The gaskets are placed in a position that lies above the inflow zone, so that the inflow zone is then isolated. The parallel valve is then brought into the open position. Additives can then be added to the drilling fluid, so that the density of the mud is thereby increased. The heavier mud is circulated down the working string and through the parallel valve to fill the annulus. As soon as the circulation of higher density drilling fluid is complete, the seals can be released from their seats and the circulation valve opened. Drilling can then continue.

An advantage of the present invention includes the use of pressure and resistivity sensors in the MWD equipment, in order thereby to allow data transmission of the corresponding measurement values in real time. Other advantages are that the present invention enables the derivation of static pressure, pressure build-up and pressure reduction with the help of the working string, such as e.g. a drill string, arranged in place. Calculation of permeability and other reservoir parameters on the basis of the pressure measurements can then be achieved without pulling out the drill string.

The gaskets can be placed many times, so that testing of several zones becomes possible. By making measurement of downhole conditions possible in real time, optimal drilling fluid levels can be determined, and this will then be of help during hole cleaning, to achieve drilling safety and higher drilling speed. When inflow of reservoir fluid and gas penetrates into the borehole, the high pressure will be held back inside the lower part of the borehole, which will significantly reduce the risk of being exposed to these pressures on the earth's surface. By shutting off the borehole immediately on the upper side of the critical zone, the volume of inflow into the borehole will also be reduced to a significant extent.

The new special features of this invention, as well as the invention itself, can best be understood from the attached drawings seen in the context of the following description where like reference signs refer to mutually like parts, and in which:

BRIEF DESCRIPTION OF THE DIFFERENT DRAWING FIGURES

Fig. 1 shows a section through part of the device according to the present invention, as it could be used together with a floating drilling rig,

fig. 2 is a perspective sketch of an embodiment of the present invention, and which includes expandable gaskets,

fig. 3 shows a section through the embodiment of the present invention which is indicated in fig. 2,

fig. 4 shows a section through the embodiment shown in fig. 3, with the addition of a sampling chamber,

fig. 5 shows a section through the embodiment shown in fig. 3, and which indicates the flow path for drilling fluid,

fig. 6 shows a section through a circulation valve and a parallel valve which can be included in the embodiment shown in fig. 3,

fig. 7 shows a section through another embodiment of the present invention, and which shows the use of a centrifugal pump to empty the intermediate annulus,

fig. 8 schematically shows control equipment and communication equipment that can be used in the present invention,

fig. 9 shows a section through part of the apparatus according to the present invention and with more than two expandable elements,

fig. 10 shows a section through the apparatus according to the present invention, and indicates an embodiment of a core drilling device,

fig. 11 is a perspective view of the apparatus according to the present invention using a non-rotating sleeve, and

fig. 12 shows a section through the embodiment shown in fig. 11.

DETAILED DESCRIPTION OF THE INVENTION

Reference should be made to fig. 1, where a typical drilling rig 2 is shown with a borehole 4 extending from it, as will be immediately understood by ordinary experts in the field. The drilling rig 2 has a working string 6 which in the embodiment shown is a drill string. The drill string 6 is applied to a drill bit 8 for drilling out the borehole 4.1 according to the present invention, other types of work strings can also be used, and can utilize spliced pipeline as well as coiled pipeline or another work string with a small diameter, straight as a damping pipe. Fig. 1 indicates the drilling rig 2 placed on a drilling ship S with a riser that extends from the drilling ship S to the seabed F.

If it is appropriate, the drill string 6 can have a downhole drilling motor 10. Embedded in the drill string 6 on the upper side of the drill bit 8 is mud pulse telemetry equipment 12 which can include at least one sensor 14, such as a core logging instrument. The sensors 14 sense the characteristics of the downhole borehole, the drill bit and the reservoir, as stick sensors will be well known within the field. The bottom assembly in the hole also contains the formation test apparatus 16 according to the present invention, which will be described in more detail below. As shown, one or more underground reservoirs 18 are penetrated by the borehole 4.

Fig. 2 shows an embodiment of the formation test apparatus 16 shown in perspective, as well as with expandable gaskets 24,26 retracted into recesses in the tool body. Stabilizing ribs 20 are also shown between the gaskets 24,26 and arranged around the tool's circumference and radially extending outwards. Also shown are inlet ports for several return flow passages 36 for drilling fluid, as well as a drawdown passage 41 which will be described in more detail below.

Reference must now be made to fig. 3, where an embodiment of the formation test apparatus 16 is shown positioned next to the reservoir 18. The test apparatus 16 contains an upper expandable gasket 24 and a lower expandable gasket 26 for sealing against the wall of the borehole 4. The gaskets 24, 26 can be expanded by means of any equipment known in the art. Inflatable packing equipment is well known in the field, as the inflation takes place by driving a pressurized fluid into the packing. Any covers for the expandable packing elements can also be included to shield the packing elements from the harmful effect of rotation in the borehole, collision with the borehole wall, as well as other forces that may be encountered during drilling or other work carried out by the drill string.

A passage 27 for high-pressure drilling fluid is formed between the longitudinal inner bore 7 and a control valve 30 with expansion element. A passage 28 for inflation fluid leads fluid from a first opening on the control valve 30 to the seals 24, 26. The passage 28 for inflation fluid branches off into a first passage branch 28A which is connected to the inflatable seal 26 and another passage branch 28B which is connected to the inflatable seal 24 A second opening on the control valve 30 is connected to a drive fluid passage 29, which leads to a cylinder 35 formed inside the outer casing for the test tool 16. A third opening on the control valve 30 is connected to a low pressure passage 31, which leads to one of several return flow passages 36. Alternatively, the low-pressure passage 31 can lead to a Venturi pump 38 or to a centrifugal pump 53, as will be discussed in more detail below. The control valve 30 and other control elements that will be described can be controlled from a downhole electronic control equipment 100 which is indicated in fig. 8, as will be described in more detail below.

It can be appreciated that the control valve 30 can optionally be set to pressurize the cylinder 35 or the seals 24, 26 with the high pressure drilling fluid flowing in the longitudinal bore 7. This can cause the piston 45 or the seals 24, 26 to stretch out to contact with the wall of the borehole 4. As soon as this expansion is achieved, adjustment of the control valve 30 can lock the relevant element in place. It can also be appreciated that the control valve 30 can optionally be set to place the cylinder 35 or the gaskets 24, 26 in fluid communication with a low pressure passage, such as the return flow passage 36. If return spring means are used in the cylinder 35 or the gaskets 24, 26, as will be well known in the art, the piston 45 will be retracted into the cylinder 35, while the gaskets 24, 26 will be retracted into their respective depressions. As will be explained below when referring to fig. 7, the low-pressure passage 31 can alternatively be connected to a suction device, such as a pump, to draw the piston 45 into the cylinder 35, or to draw the seals 24, 26 into their recesses.

As soon as the inflatable gaskets 24, 26 have been inflated, an upper annular space 32, a middle annular space 33 and a lower annular space 34 will be formed. This will be more clearly seen from fig. 5. The inflated gaskets 24, 26 insulate a part of the borehole 4 up to the reservoir 18 to be tested. As soon as the gaskets 24, 26 have been brought into contact with the wall of the borehole 4, the exact volume of the intermediate annulus 33 can be calculated, which can be utilized in pressure testing techniques.

The test apparatus 16 contains at least one fluid sensor device 46 to sense properties of the various fluids encountered. The sensor device 46 may comprise a resistivity sensor to determine the resistivity of the fluid. It can also include a dielectric sensor for sensing the fluid's dielectric properties, as well as a pressure sensor for sensing the fluid pressure. Other sensor types that can be included are measuring devices for quantity flow, viscosity sensors, density measuring devices and optical spectroscopes. A number of passages 40A, 40B, 40C and 40D are also provided for various purposes, such as extracting a pristine formation sample by means of the plunger 45, guiding fluid to a sensor 46, as well as returning fluid to the return flow passage 36. A sample fluid passage 40A passes by means of the piston 45 from its outer surface 47 to a side opening 49. A sealing element may be arranged on the outer side 47 of the piston 45 to ensure that the sample obtained consists of untouched formation fluid. This actually isolates a part of the borehole from drilling fluid or any other sources of contamination or pressure sources.

When the piston 45 is extended from the tool, the piston's side opening 49 can be aligned with a side opening 51 in the cylinder 35. A pump inlet passage 40B connects the cylinder's side opening 51 with the inlet for a pump 53. The pump 53 can be a centrifugal pump driven by a turbine wheel 55 or another suitable drive device. The turbine wheel 55 can be driven by flow through a forward passage 84 between the longitudinal bore 7 and the return flow passage 36. Alternatively, the pump 53 can be a suitable pump of another type. A pump outlet passage 40C is connected between the outlet for the pump 53 and the sensor device 46. A sample fluid return passage 40D is connected to the sensor 46 and the return flow passage 36. The passage 40D has in it a valve 48 for opening and closing this passage 40D.

As will be seen from fig. 4, a collection passage 40E may be provided for random samples and which connects the passages 40A, 40B, 40C and 40D with the lower sampling module, which is generally indicated at 52. The passage 40E leads to adjustable throttling equipment 74 and to the random sample chamber 56, for receiving a spot test. The sample collection passage 40E has within it a chamber inlet valve 58 for opening and closing the inlet to the sample chamber 56. This sample chamber 56 has a movable screen wall 72 to separate the sample fluid from a compressible fluid, such as air, thereby facilitating extraction of the random sample, as will be discussed below. An outlet passage from the sampling chamber 56 is also arranged, and is then equipped with a chamber outlet valve 62, which can be a manual valve. A test ejection valve 60 is also provided, which may be a manual valve. The passages from the valves 60 and 62 are connected to outer ports (not shown) on the tool. Valves 62 and 60 allow sampling fluid to be removed as soon as the work string 6 has been withdrawn from the wellbore, as will be discussed below. Alternatively, the sampling chamber 56 can be made extractable by means of a lead cable, by means which will be well known in the art.

When the packings 24, 26 are inflated, they will form a seal against the wall of the wellbore 4, and as they continue to expand to a fixed location, the packings 24, 26 will expand slightly into the intervening annulus 33. If fluid is trapped inside in the intermediate annulus 33, this expansion may tend to increase the pressure in the intermediate annulus 33 to a level above the pressure in the lower annulus 34 and the upper annulus 32. For operation of extensible elements, such as pistons 45, it is desirable to have the pressure in the longitudinal bore 7 in the drill string 6 is higher than the pressure in the intermediate annulus 33. A Venturi pump 33 is therefore used to prevent overpressurization of the intermediate annulus 33.

The drill string 6 contains several return flow passages 36 for drilling fluid for the purpose of allowing the return flow of drilling fluid from the lower annulus 34 to the upper annulus 32 when the seals 24, 26 are in the expanded state. A Venturi pump 38 is arranged inside at least one of the return flow passages 36, and its structure is designed to form a zone of lower pressure, which can then be used to prevent overpressurization in the intermediate annulus 33, via the downdraft passage 41 and the downdraft control valve 42. In a similar way, the Venturi pump 38 can be connected to the low-pressure passage 31, so that the low-pressure zone formed by the Venturi pump 38 can be used for retracting the piston 45 or the seals 24, 26. Alternatively, and as explained below when referring to fig. 7, another type of pump can be used for this purpose.

Several return flow passages can be arranged, as shown in fig. 2. One of the return flow passages 36 is used to drive the Venturi pump 38. As shown in FIG. 3 and fig. 4, the return flow passage 36 has a generally constant internal diameter until the Venturi restriction 70 is encountered. As shown in fig. 5, drilling fluid is pumped down the longitudinal bore 7 in the work string 6 to exit near the lower end of the drill string at the drill bit 8, for return upwards in the annular region, as indicated by the flow arrows. Assuming that the inflatable packings, 24, 26 have been set and that a seal has been established against the wellbore 4, then the annular flow will be diverted through the return flow passages 36. As this flow approaches the venturi constriction 70, a pressure drop will take place, so that the Venturi effect will produce a low-pressure zone in the Venturi. This low-pressure zone communicates with the intermediate annulus 33 through the downdraft passage 41, and thus prevents any overpressurization of the intermediate annulus 33.

The return flow passage 36 also contains a valve 39 and an outlet valve 80 for opening and closing the return flow passage 36, so that the upper annulus 32 can be isolated from the lower annulus 34. The bypass passage 84 connects the longitudinal bore 7 in the drill string 6 with the return flow passage 36 .

Reference must now be made to fig. 6, where yet another possible distinctive feature of the present invention is shown, and where a circulation valve 90 is installed in the drill string 6 to open and close the inner bore 7 in the drill string 6. It also includes a parallel valve 92, arranged in the parallel passage 94, to enable flow from the inner bore 7 in the drill string 6 to the upper annulus 32. The rest of the formation tester is then carried out in the same way as previously described.

The circulation valve 90 and the parallel valve 92 are operationally coordinated with the control equipment 100. To operate the circulation valve 90, a mud pulse signal is transmitted down the hole, thereby giving a signal to the control system 100 to change the setting of the valve 90. The same sequence will be necessary for to control the parallel valve 92. Fig. 7 shows alternative means of performing the functions which have taken place by means of the Venturi pump 38. The centrifugal pump 53 has its inlet connected to the downdraft passage 41 and the low pressure passage 31. A downdraft valve 57 and a test inlet valve 59 are arranged in the pump inlet passage to the intermediate annulus and the piston respectively. The pump inlet passage is also connected to the low-pressure side of the control valve 30. This enables the use of the pump 53, or another similar pump, for extracting fluid from the intermediate annulus 33 through the valve 57, to extract a sample of formation fluid directly from the formation through the valve 59 , or to pump down the cylinder 35 or the seals 24, 26. Fig. 7 also shows equipment for applying fluid pressure to the formation, either through the intermediate annulus 33 or via the sample inlet valve 59. The purpose of applying this fluid pressure can either be to fracture the formation, or to carry out a pressure test on it. A pump inlet valve 120 and a pump inlet valve 122 are respectively arranged in the inlet and outlet of the pump 53. The pump inlet valve 120 can be adjusted as shown to bring the pump inlet flush with the low pressure passage 31, as is necessary for the work operations described above. Alternatively, the inlet valve 120 can be turned a quarter turn clockwise by the control device 100 to bring the pump inlet flush with the return flow passage 36. In a similar manner, the pump outlet valve 122 can be positioned as shown to bring the pump outlet flush with the return flow passage 36, as required for the work operations described above. Alternatively, the pump outlet valve 122 can be turned a quarter turn clockwise by the control gear 100 to bring the pump outlet flush with the low pressure passage 31. At the pump inlet valve 120 arranged to connect the pump inlet together with the return flow passage 36 and the pump outlet valve 122 set to bring the pump outlet into connection with the low pressure passage 31, the pump 53 can be driven to withdraw fluid from the return flow passage 36 for pressurization of the formation via the low pressure passage 31. Pressurization of the formation can be produced through the extendable piston 45 with the sample inlet valve 59 open and the drawdown valve 57 closed. Alternatively, pressurization of the formation can be produced through the annulus 33, and then with the sample inlet valve 59 closed and the drawdown valve 57 open.

As indicated in fig. 8, the invention includes the use of control equipment 100 to regulate the various valves and pumps, as well as to receive the output signals from the sensor device 46. The control equipment 100 is able to process the sensor information using the downhole microprocessor/regulator 102, and to deliver the relevant data to the communication interface 104, so that the processed data can then be telemetered at the earth's surface using normal technology. It should be noted that different forms of transfer energy can be used, such as siampulses, as well as acoustic, optical or electromagnetic equipment. The communication interface 104 can be powered by a downhole electrical power source 106. This power source 106 can also supply power to the flowline's foot device 46, the microprocessor/regulator 102, as well as the various valves and pumps.

Communication with the earth's surface can be achieved by means of the working string 6 and then in the form of pressure pulses or by other means, as will be well known in the field. When it comes to mud pulse generation, the mud pulses will be received on the earth's surface via a two-way communication interface 108. The data thus received will be sent to the surface computer 110 for interpretation and display.

Command signals can be sent down the fluid column using the communication interface 108 to be received by the communication interface 104 down the borehole. The signals thus received are transmitted to the microprocessor/regulator 102 down in the borehole. The regulator 102 will then give signals to the relevant valves and pumps for operation as desired.

The downhole microprocessor/controller 102 may also contain a pre-programmed sequence of process steps based on predetermined criteria. As downhole data, such as data for pressure, resistivity, flow rate, viscosity, density, spectral analysis or other data from an optical sensor, or dielectric constants, is received, the microprocessor/regulator will therefore automatically send command signals using the control equipment for to handle the various valves and pumps.

As shown in fig. 9, it may be appropriate to have two or more sets of expandable gaskets with associated test equipment 16 between them. One set of gaskets may isolate a first formation, while another set of gaskets may isolate a second formation. The apparatus can then be used to pump formation fluid from the first formation into the second formation. This function can be carried out either from an annular space 33 at the first formation to another annular space 33 at the second information, using the extended gaskets for isolating the formations. Alternatively, this function can be performed via sample fluid passages 40A in the two sets of sample apparatus 16, using the extended pistons 45 for isolation of the formations. Reference should again be made to fig. 7, from which it will appear that in the first set of test apparatus 16 can e.g. the sample inlet valve 59 be closed and the drawdown valve 57 open. With the pump inlet valve 120 and the pump outlet valve 122 set as shown in fig. 7, the pump 53 can be driven to pump formation fluid from the annulus 33 at the first formation into the return flow passage 36. This return flow passage 36 can then extend through the working string 6 to the second set of test equipment 16 at the second formation. There, the second test inlet valve 59 can be closed while the second pull-down valve 57 can be open just like in the first set of test apparatus 16.1 the second set of test apparatus 16, however, the pump inlet valve 120 and the pump outlet valve 122 can be turned a quarter of a turn in the clockwise direction to make it is possible for the second pump 53 to pump the first formation fluid from the return flow passage 36 into the second formation via the second drawdown valve 57 and via the annulus 33. Variants of this process can be used to pump formation fluid from one or more formations into one or several other formations. At the lower end of the working string 6, it may only be necessary to have one easily expandable gasket to be able to isolate the lower annulus.

As shown in fig. 10, it may also be appropriate to include a core drilling device 124 for the formation in the test apparatus 16 according to the present invention. The core drilling device 124 can be introduced into the formation using equipment of the same type as the equipment described above for extending the piston 45. The core drilling device 124 can be rotated by a turbine 126 which is driven by drilling fluid through the central borehole 7 and a turbine inlet port 128. The outlet from the turbine 126 may be through an outlet passage 130 and a turbine control valve 132, which is then controlled from the control equipment 100. With the gaskets 24, 26 expanded, the coring device 124 is extended and rotated to extract a pristine core sample from the formation. This core sample can then be drawn back into the working string 6, where a certain chemical analysis can be carried out, if desired, and the core sample can there be retained in its pristine state, including pristine formation fluid, for extraction after the return of the sampling apparatus 16 to the earth's surface.

As shown in fig. 11, the apparatus of the present invention may be modified by the use of a sliding, non-rotating sleeve 200 to enable sampling while drilling or other rotation of the drill string is taking place. A retractable stabilizer vane 216 can be placed on the side of the test tool opposite the test port, for the purpose of pushing the test port against the borehole wall, in which case no piston is used, or to center the test tool in the borehole. An upper stabilizer 220 and a lower stabilizer 222 can additionally be applied to the drill string 6 to separately stabilize the rotating part of the work string.

Fig. 12 shows a longitudinal section through the embodiment of the test apparatus 16 which has a sliding, non-rotating sleeve 200. This cylindrical non-rotating sleeve 200 is placed in a recess in the outer surface of the working string 6. The space between the -rotating sleeve 200 and the work string are sealed by an upper rotatable seal 202 and a lower rotatable seal 204. Several other rotatable seals 206, 208, 210, 212, 214 can be used to seal fluid passages leading from the inner bore in the work string to the test apparatus 16, depending on the particular configuration of the relevant test apparatus used. The non-rotating sleeve 200 is shorter than the recess in which it is placed, thereby allowing the working string 6 to move axially in relation to the stationary sleeve 200, as the working string 6 is advanced during the boring. A spring 223 is arranged between the upper end of the sleeve 200 and the upper end of the socket, thereby biasing the sleeve 200 in a downward direction relative to the working string 6.

One or more extendable stabilizing vanes or ribs 216 may be provided on the non-rotating sleeve 200, on the side opposite the sample piston 45 or sample port rib 20. A remote controlled rib extension valve 218 may be provided in a passage 219 leading from the working string's bore 7 to an expansion chamber 221 in which the extendable rib 216 is located. Opening the rib extension valve 218 introduces pressurized drilling fluid into the expansion chamber 221, so that the extendable rib 216 is hydraulically driven to move outwards into contact with the borehole wall. Plant shoulders or limiting devices known in the art (not shown) may be provided on the extendable rib 216 and the non-rotating sleeve 200 to limit the range of motion of the extendable rib 216. Furthermore, a spring or formed biasing element which is known in the field (not shown) to be arranged to bring the extensible rib 216 back to its rest position after equalizing the hydraulic pressure.

WORK FUNCTION

In operation, the formation sampler 16 is positioned up to a selected formation or a selected reservoir. A hydrostatic pressure is then measured using the pressure sensor located inside the sensor device 46, while the resistivity of the drilling fluid at the formation is determined. This is achieved by pumping fluid into the test device 46, and then stopping to measure pressure and resistivity. This data is processed down the borehole and is then stored or transmitted up the borehole using the MWD telemetry equipment.

The operator will then expand and adjust the inflatable gaskets 24, 26. This is done by keeping the work string 6 stationary and circulating the drilling fluid downwards in the inner bore 7, through the drill bit 8 and upwards in the annular space. The valves 39 and 80 are open, and the return flow passage 36 will therefore be open. The control valve 30 is adjusted to bring the high pressure passage 27 flush with the inflation fluid passages 28A, 28B, and drilling fluid is then allowed to flow into the packings 24, 26. Because the pressure drop from the interior of the borehole 7 to the annulus above the bit 8 will be a significant pressure difference to expand the seals 24, 26 to produce a good seal. The higher the quantity flow of drilling fluid, the higher the pressure drop will be, and the higher the expansion force applied to the seals 24, 26 will be. In the version with a non-rotating sleeve, the expansion of the gaskets 24, 26 can be used to stop and prevent rotation of the test apparatus 16. When the gaskets 24, 26 are withdrawn, the sleeve 200 will rest on the lower end of the socket on the working string 6 The seals 24, 26 are activated from hydraulic equipment controlled by the downhole electronics. As the working string 6 is advanced during the drilling, the sleeve 200 will remain stationary in relation to the drill hole while the spring 223 is compressed. The sleeve 200 will thus be mainly decoupled from the movement of the drill string 6, which makes it possible to carry out test measurements on the formation, without being affected by the movement of the working string 6. It will therefore not be necessary to interrupt the drilling process. As soon as the testing of the formation is complete, the packing 24, 26 is withdrawn. The spring 223 or other biasing device known in the art will then push the sleeve 200 towards the lower end of the recess on the working string 6. As an alternative to expanding the gasket, or in addition to this, another extendable element, such as the piston 45 is extended to form contact with the wall of the borehole, by corresponding position setting of the valve 30. If no gaskets are expanded, then the extensible rib 216 alone can be used to keep the non-rotating sleeve 200 stationary.

The upper packing element 24 can have a larger width than the lower packing 26, and thereby contain a larger volume. The lower gasket 26 will therefore be fitted first. This can prevent waste from being trapped between the seals 24, 26.

The Venturi pump 38 can then be used to prevent overpressurization in the intermediate annulus 33, or the centrifugal pump 53 can be operated to remove drilling fluid from the intermediate annulus 33. This is achieved by opening the drawdown valve 41 in the embodiment shown in fig. 3, or by opening the valves 82, 57 and 48 in the embodiment shown in fig. 7.

If the fluid is pumped from the intermediate annulus 33, the resistivity and dielectric constant of the fluid that is extracted can be continuously monitored by the sensor device 46. The thus measured data can be processed downhole and transmitted up the borehole using the telemetry equipment. The resistivity and dielectric constant of the fluid passing by will change from the values for the drilling fluid to the values for the drilling fluid filtrate, and from there to the values for the untouched formation fluid.

In order to create a buildup of formation pressure and draw down samples, the operator closes the pump inlet valve 57 and the parallel valve 82. This stops the emptying of the intermediate annulus 33 and enables an immediate build-up of the pressure to the untouched pressure of the formation. The operator can choose to continue circulation to telemeter the pressure results uphole.

In order to take a random sample of formation fluid, the operator can open the chamber inlet valve 58 so that the fluid in the passage 40E is allowed to enter the random sample chamber 56. This random sample chamber can be emptied or filled with some compressible fluid. If the sampling chamber 56 is empty and is under atmospheric conditions, the shield plate 72 will be driven downwards until the chamber 56 is filled. An adjustable throttle 74 is included to regulate the flow into the chamber 56. The purpose of the adjustable throttle 74 is to regulate the pressure change across the gaskets when the sampling chamber is opened. If the throttle 74 did not exist, then the packing seal could be lost due to the sudden change in pressure created by opening the sampling chamber inlet valve 58. Another purpose for the throttle 74 could be to regulate the process when fluid flows into the equipment, thereby preventing the pressure from being lowered below the fluid's bubbling point, so that gas evaporation from the fluid is thereby prevented.

As soon as the sampling chamber 56 is filled, the valve 58 can be closed again, which will enable another pressure build-up, which is then monitored by the pressure sensor. If desired, several pressure build-up tests can be performed by repeatedly pumping down the intermediate ring mold 33, or by repeatedly filling additional test chambers. The permeability of the formation can be calculated by later analyzing the pressure as a function of time data, such as by means of a Horner plot, which will be well known in the art. In accordance with the teachings of the present invention, data can of course be analyzed before the seals 24 and 26 are emptied. The stab sample chamber 56 can be used for the purpose of achieving a fixed and regulated drawdown volume. The withdrawn fluid volume can also be obtained from a downhole turbine meter placed in the relevant passage.

As soon as the operator is prepared to drill further, or alternatively to test another reservoir, the seals 24, 26 can be emptied and retracted, so that the test apparatus 16 then returns to standby mode. If the piston 45 is used, it can be withdrawn. The gaskets 24, 26 can be emptied by positioning the control valve 30 to bring the low pressure passage 31 in line with the inflation passage 28. The piston 45 can be retracted by positioning the control valve 30 to bring the low pressure passage 31 in line with the cylinder passage 29. To total to be able to empty the seals or the cylinder, however, the Venturi pump 38 or the centrifugal pump 53 can be used.

Once it has reached the ground surface, the sample chamber 56 can be separated from the working string 6. In order to empty the sample chamber, a container to contain the sample (which is still at formation pressure) is attached to the outlet of the chamber outlet valve 62. A source for compressed air is attached to the discharge valve 60. When the discharge valve 62 is opened, the internal pressure is released, but the sample will still be in the sample chamber. The compressed air is brought into connection with the ejection valve to push the screen plate 72 towards the outlet valve 62, which will then drive the sample out of the sample chamber 56. This sample chamber can be cleaned by refilling with water or solvent through the outlet valve 62, as well as by moving the screen plate 72 forward and back using compressed air via the exhaust valve 60. The fluid can then be analyzed with regard to hydrocarbon number distribution, bubble point pressure, or other properties. Alternatively, a sensor package can be coordinated with the sampling chamber 56, so that the same measurements can be carried out on the fluid sample while it is still down in the borehole. The sample can then be unloaded down the borehole.

As soon as the operator has decided to adjust the density of the drilling fluid, the method comprises process steps which involve measuring the hydrostatic pressure in the borehole at the target formation. The gaskets 24, 26 are then set so that an upper 32, a lower 34 and a middle annulus 33 are formed inside the borehole. Drilling well fluid is then extracted from the intermediate annulus in the same way as previously described, and the formation pressure is measured inside the intermediate annulus 32. The other designs of expandable elements can also be used to determine the formation pressure.

The method further comprises steps which involve adjusting the density of the drilling fluid in accordance with the pressure readings from the formation, so that the mud weight of the drilling fluid is in close accordance with the pressure gradient of the formation. This then enables maximum drilling efficiency. The inflatable gaskets 24, 26 are then emptied as previously explained, and drilling is resumed with drilling fluid that has optimal density.

The operator will be able to continue the drilling to a second underground horizon, and at the horizon in question can take another hydrostatic pressure measurement, as well as pump up the seals 24, 26 and empty the intermediate annulus 33, as previously stated. The density of the drilling fluid can then be readjusted in accordance with the pressure measurement, after which the inflatable gaskets 24, 26 are retracted and the drilling of the borehole can continue with the correct overbalance weight.

As the object of the invention is described here, it can also be used to prevent blowout near the drill bit. If an underground blowout were to occur, the operator would be able to set the inflatable seals 24, 26 and bring the valve 39 to the closed position, as well as begin the circulation of drilling fluid down the work string through the open valves 80 and 82. It should be noted that when used as a blowout barrier the pressure in the lower annulus 34 is monitored by opening valves 39 and 48 and closing valves 57, 59, 30, 82 and 80. The pressure in the upper annulus can be monitored during direct circulation to the annulus through the bypass valve by opening valve 48. Also the pressure in the inner channel 7 in the drill string can be monitored during normal drilling by closing both the inlet valve 39 and the outlet valve 80 in the passage 36, as well as by opening the bypass valve 82 with all the other valves closed. Finally, the bypass passage 84 will enable the operator to circulate fluid with greater density to gain control over the well kick.

If the embodiment shown in fig. 6 is used, then the operator will alternatively be able to set the first and second inflatable packing 24, 26 and then bring the circulation valve 90 into the closed position. The inflatable gaskets 24, 26 are set in a position that lies above the inflow zone, so that this inflow zone is isolated. The parallel valve 92 which is located on the drill string 6 is placed in the open position. Additives can then be added to the drilling fluid on the soil surface and thereby increase its density. The heavier drilling fluid is circulated downwards in the working string 6 and through the parallel valve 92. As soon as the drilling fluid with greater density has replaced the lighter fluid, the inflatable gaskets 24, 26 can be retracted and the circulation valve 90 is then placed in the open position. Drilling can then be resumed.

Although the invention shown herein and described in detail is fully capable of achieving the objects and exhibits the advantages set forth above, it should be understood that this description is only illustrative of the presently preferred embodiments of the invention, and is in no way intended to indicate any limitations other than those appearing in the subsequent patent claims.

Claims (10)

1. Method for testing a formation comprising: submerging a drill string (6) in a drill well, said drill string including a drill bit, a first expandable element (45) extending from the drill string, a gate (51), and a first fluid transfer device (53); drilling a borehole (4); extending a first set of gaskets (24, 26) to isolate a first portion of the borehole until a first formation; positioning the first expandable member (45) between the first set of gaskets (24, 26) and next to the first formation (18); and expanding the first expandable element (45) into a sealing abutment against a wall in the borehole (4); characterized by: expanding a second set of gaskets (24, 26) to isolate a second part of the borehole up to a second formation; positioning the second expandable element (45) between the second set of gaskets (24, 26) and next to the second formation (18); and expanding the second expandable element (45) and a second port for sealing against a wall in the borehole (4); and transferring formation fluid from the first formation to the second formation through first and second ports. 2. Method according to claim 1, further characterized by: applying fluid via said first port with the first fluid transfer device (53). 3. Method according to claim 1, further characterized by: fracturing of said first isolated part of the borehole (4) with said fluid at a high pressure. 4. Method according to claim 1, further characterized by: providing a pressure sensing device (16) in the drill string (6), further comprising pressurizing the first isolated portion of the wellbore to a selected test level; and to monitor the pressure in the first isolated part of the borehole with said pressure sensing device (16) to sense a pressure drop. 5. Method according to claim 1, further characterized by: extending a core drilling device between at least one of the first set of gaskets and the second set of gaskets; and taking a core sample from at least one of the first selected formation and the second selected formation. 6. Apparatus for testing a formation comprising: a drill string (6) for sinking into a borehole, the drill string including a drill bit, a first set of expandable packings (24, 26) extending from the drill string to isolate a first portion of the borehole adjacent a first selected formation (18), a first port and a first fluid transfer device expandable between the first set of gaskets and to a wall in the borehole for sealing engagement of the expandable element against the wall in the borehole (4), characterized by second sets of expandable gaskets (24, 26) extending from the drill string to position said second expandable member (45) and a second port between the second set of gaskets adjacent a second formation (18) for sealing against the wall of the borehole (6) to isolating the second formation from the first formation; a second gate; and means for transferring fluid from the first formation (18) to the second formation (18) through first and second ports. 7. Apparatus as stated in claim 6, further characterized by: a high-pressure fluid applied via said first port with said fluid transfer device (53). 8. Apparatus as stated in claim 6, further characterized by: a device for fracturing said first isolated part of the borehole with said high-pressure fluid. 9. Apparatus as stated in claim 6, further characterized by: a pressure sensing device (16) in the drill string (6), further comprising a device for increasing the pressure (53) in said first isolated part of the drill well to a selected test level; and a device for monitoring the pressure (16) in the first isolated part of the borehole with said pressure sensing apparatus to sense a pressure drop. 10. Apparatus as specified in claim 6, further characterized by: a core drilling device (124) arranged between at least one of the first set of gaskets and the second set of gaskets.