To ensure the safe and efficient operation of down-hole drilling in drilling rigs or work-over rigs, a fluid generally referred to as a drilling mud or simply mud is circulated into and out of the bore-hole being drilled or a bore-hole which has already been drilled. The drilling mud is designed to match the chemical and physical environment of the particular well or type of well being drilled or which has already been drilled. Generally the drilling mud is pumped into and out of the well by a so-called mud pump through the drill string and back up out through the annulus (formed between the drill string and the circumference of the well) of the well where the drilling mud is deposited into a system of surface tanks, filters etc, before being re-circulated down-hole. The mud forms in use a column of fluid that creates a positive hydrostatic pressure within the well bore which allows wells to be drilled and/or repaired safely and efficiently.

As the mud is circulated within the well bore, materials such as brine, silt and rock are removed from the well bore to the surface by the circulating mud. The inclusion of such materials can have a detrimental effect on desired properties, such as viscosity and density, of the drilling mud. To ensure the desired properties of the drilling mud are maintained within operational parameters, measurements of these properties are made at regular intervals by on-site personnel.

The density of the drilling mud may be determined for example

by using a mud balance instrument, and viscosity may be checked using a Marsh Funnel. The measurement of the density and viscosity of a drilling mud are generally made every half- hour or so and the results are generally considered to be representative of all of the drilling mud being circulated within the system at that particular time. However, the physical and chemical properties of the drilling mud may vary considerably over a given period of time between each batch test of viscosity and/or density of the drilling mud. Such variances are not be desirable, particularly where the viscosity and/or density deviate from operationally acceptable parameters. Other more thorough and time consuming checks (often referred to as mud tests or mud checks) on the various desired properties of the drilling mud are generally made to complement the regular batch testing of for example the density and viscosity of a drilling mud. Again however, such testing is on a batch-by-batch basis and repeated only over time periods of at least every few hours or so. Such mud tests/checks require the attention of skilled personnel for relatively long periods of time, and although the results of the mud tests/checks are of particular importance to the continuing safe and efficient operation of the drilling operation, the results are generally only relevant to the particular batch of drilling mud which has been checked, and cannot be viewed as being representative of the drilling mud as a whole between such mud tests/checks.

It will of course be appreciated that there are a number of physical properties of a drilling mud which are required to be checked more or less frequently, however, the inventor has found that in order to ensure the safe and efficient operation of a drilling device using a said drilling mud then it is highly desirable to more or less continuously monitor the viscosity and density of the drilling mud as it is being used

as these characteristics are particularly critical to the efficiency of the mud.

It is an object of the present invention to avoid or minimise one or more of the disadvantages of known procedures.

In a first aspect the present invention provides an apparatus suitable for use in substantially continuous measurement of a physical property of a drilling mud during use thereof in a drilling mud flow circuit of a drilling device, said apparatus comprising: -a sample chamber having an inlet and an outlet, the sample chamber being arranged to allow, in use of the apparatus, a drilling mud to flow therethrough from said inlet to said outlet; -a detector device formed and arranged for substantially continuous measurement of a physical property of a drilling mud flowing through the sample chamber in use of the apparatus; -supply and return conduits formed and arranged for connection of said inlet and outlet respectively, in use of the apparatus, to said drilling mud flow circuit for delivering at least part of the drilling mud flow through said apparatus; and -a pump formed and arranged for providing a controlled flow of the diverted drilling mud through the apparatus in use thereof.

Desirably the physical property of the drilling mud to be measured is one or both of viscosity and density.

By substantially continuous measurement of a said physical property, individual measurement of said physical property may be made sequentially one after the other with little or no

time interval between each said measurement i. e. in near real time. It will of course be appreciated that a time interval between individual measurements can exist and that such a time interval may be varied as required from 30 seconds to 30 minutes between individual measurements.

The flow circuit of drilling mud is intended to refer to the piping, the drill string (where appropriate), the annulus between the drill-string and bore-hole and any other conduit (s) and apparatus including reservoirs used to carry or direct the drilling mud in use thereof.

The sample chamber is desirably in the form of an elongate housing having said inlet at one end thereof and said outlet at the other end thereof. The housing may be of any shape in cross-section, preferably generally circular, square, rectangular, triangular, oval, regular and irregular polygonal shapes may also be considered.

Preferably the sample chamber is in the form of an elongate cylinder having a longitudinal extent between the inlet and outlet thereof.

It will of course be realised that the sample chamber will be constructed from a material which is capable of withstanding above atmosphere pressures and be more or less robust and resistant to corrosion. Preferred materials such as steel, particularly stainless steel (especially for use in hostile environment such as those found or sea-based drilling rigs) are suitable for construction of the sample chamber.

Preferably, the sample chamber is arranged so that the inlet is raised vertically relative to the outlet thereof wherein an angle a is defined as the angle between the longitudinal

extent of the sample chamber which extends between the inlet and the outlet, relative to the horizontal or vice versa i. e. the outlet is raised above the inlet so that the sample chamber is disposed at the angle a relative to the horizontal.

Preferably the angle a is from 30° to 90°, more preferably from 45° to 80° and more preferably from 55° to 70°.

Where the sample chamber is arranged at an angle a relative to the horizontal, this has the advantageous effect of minimising the settlement of various solid/semi-solid components such as baryte (Barium Sulphate which is used to inter alia, increase the density of the drilling mud) from the drilling mud when the flow-rate of drilling mud through the sample chamber is very low or has stopped altogether. Advantageously this prevents settlement around the detector device thereby minimising the risk of inaccurate measurements being taken.

The sample chamber being arranged at angle a relative to the horizontal allows any such solids/semi-solids to move away under the influence of gravity from the inlet towards the outlet (or vice versa) of the sample chamber, and thereby leaving the sample chamber relatively free of any said solids/semi-solids which may precipitate or settle therefrom.

The detector device is formed and arranged for continuous measurement of physical properties such as density and viscosity, preferably both density and viscosity.

The detector device may be any device suitable for direct and/or indirect continuous measurement of a physical property of a said drilling mud as it passes through the sample chamber. Where the detector is formed and arranged to measure said physical property directly, then preferably the detector is arranged to detect the density and/or viscosity of the

drilling mud. More preferably, the device is also arranged to measure the dynamic and kinematic viscosity, and even more preferably to also measure the temperature of the drilling mud. Desirably the detector device is in the form of a viscometer and/or a densiometer.

Preferably, the detector device has a detector or measurement portion in the form of a tuning fork having a pair of parallel tines. The tines are inserted into the interior volume of the sample chamber and into a flow of the drilling mud for direct measurement of a said physical property when in contact with the drilling mud. Indirect measurement of said physical property by the detector device may be achieved by forming and positioning the detector device, or at least a detector portion thereof, adjacent or against the sample chamber wherein, in use, the detector device obtains inductive or capacitive measurements of the drilling mud passing through the sample chamber and derives or quantifies a said physical property therefrom.

It will of course be appreciated that the detector device may utilise a combination of both direct and indirect measurements of one or more physical properties of the drilling mud.

Desirably, the detector device of the present invention is provided with suitable display and/or recording apparatus so that the measurements of said physical properties can be monitored and/or recorded. Suitable display/recording apparatus include for example data loggers, personal computers, VDU's, printer devices etc. and any other similar device (s) which can be viewed preferably remotely e. g. in the mud pit or shaker house of a drilling rig; or viewed when adjacent the apparatus.

The supply and return conduits for connection of the inlet and outlet to said drilling mud flows circuit may be in the form of flexible or rigid pipes or hoses which can be connected to the drilling mud flow circuit by suitable connector devices such as screw fittings. Desirably the supply conduit, at least, is connected to the drilling mud flow circuit, in use, at a point thereon so as to deliver said at least part of the drilling fluid to the apparatus from said point wherein the drilling mud is representative of the drilling mud exiting a bore-hole or other area of operation where the drilling mud is being used. By connecting the supply conduit, at least, to a said point in the drilling mud flow circuit a more accurate and precise i. e. a representative, measurement of the physical properties of the drilling mud being used within the drilling mud flow circuit.

The pressure of drilling mud within the sample chamber, in use, is desirably within the range of from 1 to 10bar (1- 10x105 N/m2) and preferably from 3 to 4bar (3-4x105 N/m2). The flow rate of drilling mud, in use, flowing through the sample chamber is preferably from 5 to 50 1/min and most preferably from 10 to 30 1/min.

The pressure within the sample chamber may be varied by the provision of an adjustable flow valve or other suitable throttling means disposed at or down-stream from the outlet of the sample chamber. In use, the adjustable valve can be opened or closed incrementally so as to reduce or produce a back-pressure within the sample chamber as a drilling mud flows therethrough. By providing a backpressure within the sample chamber, entrained gases (or at least a proportion thereof) are reduced in volume or dissolved into solution with the mud as a result of the increase in pressure acting thereof. Additionally, or alternatively dissolved gases may

also be prevented from being displaced from solution by a said backpressure within the sample chamber. It is desirable to minimise the presence of entrained gases within the drilling mud as it passes through the apparatus more particularly through the sample chamber, as the presence of bubbles of gas may lead to spurious measurements of the physical properties of the drilling mud. Such spurious measurement are clearly undesirable as they may lead operating personnel to take unrequired correctional measures to bring the measured physical property back within operating parameters.

The pump for providing a controlled flow of said directed drilling mud through the apparatus may be located upstream or downstream of the sample chamber. Preferably the pump is located upstream of the sample chamber i. e. before the inlet of the sample chamber.

The pump can be of any known type suitable for use in pumping drilling muds. However, it will be appreciated that it is desirable to provide pumps which are intrinsically"safe"for use in environments such as oil/drilling-rigs i. e. pumps which have a negligible or reduced possibility of providing an ignition source for combustible materials e. g. hydrocarbon gases/liquids which are generally found on oil/drilling-rigs.

Particularly suitable pumps are pneumatically driven diaphragm pumps. Desirably, said pneumatically driven diaphragm pumps are driven by compressed air provided from a compressed air source such as for example a cylinder containing compressed air or a compressor unit.

Preferably the pump produces a flow-rate of drilling mud which is substantially free of flow-rate surges. Where a pump cannot produce a surge-free flow of, drilling mud, then the

pump may be fitted with a device such as a pulsation dampner to dampen any such flow-surges.

As will be appreciated, drilling muds may contain large amounts of solid and/or semi-solid materials when the mud returns to, for example, a drilling rig during a drilling operation. In order to reduce the possibility of damage to the apparatus in use thereof, especially to the detector device and the pump the apparatus may be provided with one or more filters disposed up-stream of the sample chamber, wherein the filters are formed and arranged to remove unwanted solid and/or semi-solid materials from a said diverted mud flow passing through the apparatus. Preferably, the filters are directional in that they will allow only a fluid to pass in one direction therethrough. Desirably there is used a Y' type strainer of generally known type and construction.

Desirably the apparatus is formed and arranged in a compact and portable form which can be relatively easily transported to and from a rig site without the need for heavy lifting equipment. Preferably the apparatus is transportable in a small trailer capable of being towed behind a private or light goods vehicle.

In a further aspect, the present invention also provides a method of substantially continuously measuring a physical property of a drilling mud during use thereof in a drilling mud flow circuit of a drilling device, said method comprising the steps of: a) providing an apparatus according to the present invention; b) providing a drilling mud flow circuit; c) attaching the supply and return conduits of said apparatus to said drilling mud flow circuit;

d) pumping drilling mud from the drilling mud flow circuit to provide a flow of drilling mud through the sample chamber; and; e) obtaining from the detector device substantially continuous measurements of a said physical property of the drilling mud as it passes through the sample chamber.

Desirably the apparatus is provided with an audio and/or visual alarm to notify operator personnel when a measured physical property falls out with a pre-defined operational parameter.

Preferably the apparatus of the present invention forms part of an"active"control system, wherein the apparatus is formed and arranged with a control mechanism which adjusts the composition or other physical property of a drilling mud when the apparatus detects that a physical property to be measured falls outwith pre-defined operational parameters, so that the physical property is brought within said operation parameter.

The apparatus is preferably provided with an additional'fluid feed inlet in fluid communication with the sample chamber wherein the inlet is formed and arranged to provide an additional volume of drilling mud to the sample chamber if required.

Further preferred features and advantages of the present invention will appear from the following detailed description given by way of some preferred embodiments illustrated with reference to the accompanying drawings in which: Fig. 1 shows a block flow diagram of an apparatus according to the present invention; Fig. 2 shows a perspective view a first embodiment of the apparatus;

Fig. 3 shows a top plan view of the apparatus shown in Fig. 2; Fig. 4 shows a top perspective view of a filter box shown in an open condition; Fig. 5 shows a suitable side view of an apparatus according to a second embodiment of the present invention; and Fig. 6 is a schematic side view of a third embodiment of the invention.

Fig. 1 shows a block flow diagram of an apparatus generally referred to by reference number 100. The apparatus 100 comprises an inlet pipe 102 having a first end 103a connected to drilling mud flow circuit (not shown) and at a second end 103b in fluid communication with a first two way fluid diverter valve 104.

The first diverter valve 104 in a first position directs a drilling mud in the direction of arrow A'towards a first filter box 106. In a second position, the first diverter valve 104 directs drilling mud in the direction of arrow B' towards a second filter 110. A second two-way fluid diverter valve 108 is located down-stream from the first and second filters 106,110 so that in use one of the two filters 106,110 can be isolated, and the flow of drilling mud diverted through one of the filters 106,118 not being cleaned. In this arrangement, the filters 106,110 can be cleaned individually whilst the apparatus 100 can be operated substantially continuously.

A diaphragm pump 112 is arranged to draw drilling mud from the inlet 103a at a flow rate of between 10 and 30 1/min. The pump is arranged in a series with a pulsation dampener 112a and pumps via an inlet opening 113 drilling mud to a sample chamber 114 arranged down-stream from both the pump 112 and the pulsation dampener 112a. The dampner 112a serves to

reduce or minimise any flow-rate surges produced by operation of the pump 12.

Both the pump 112 and pulsation dampener are air driven via compressed air-lines 112b connected to cylinders (not shown) containing compressed air.

The sample chamber 114 has an adjustable flow valve 124 disposed at an outlet 122, wherein the adjustable flow valve 124 is formed to create a back-pressure of between 3 to 4 bar (3 to 4x105 N/m2) within the sample chamber so as to minimise the effects of entrained gases in the mud on the measurement of viscosity and density of a drilling mud within the sample chamber 114 by a combined viscometer/densiometer device 116 attached thereto.

The combined viscometer/densiometer 116 is a Solartron type 7827 viscometer (produced by Solartron Transducers of Hampshire, UK) which has a detector turning-fork shaped portion (not shown) which extends into the inner volume of the sample chamber 114. The combined viscometer/densiometer 116 is in electrical communication with a power flow cut-out device 117 which is arranged to cut-off the source of compressed air to the apparatus 100 if no drilling mud is detected within the sample chamber 114.

The combined viscometer/densiometer device 116 is provided with a data display unit 117 and a data recorder unit 119 and in electrical communication therewith via cables 120. The data display and recorder unit 117,119 display and records measurements obtained by the viscometer/densiometer device 116 which are processed via a signal connector (not shown) specifically a 7954V signal connector (Solartron Transducers).

A flow meter 115 is provided in-line down-stream from the adjustable flow valve 124. The flow meter 115 is used to display on a panel (not shown) the flow-rate of drilling mud flowing through the apparatus 100 towards an exit pipe 126 which connects the apparatus 100 back into the drilling mud flow circuit.

Figs. 2 and 3 shows the apparatus 100 according to a first embodiment of the present invention wherein the filters 106 and 110 are individually isolatable by the replacement of bi- detectional valves 104 and 108 with stop valves 128a, b and 130a, b (see also Fig. 3) respectively, to allow for individual isolation and cleaning (or replacement) of the filters 106,110.

Each rectangular section filter box 106,110 contains a rectangular planar filter element 132a, b (Fig. 4) arranged on one long edge thereof to extend into diametrically opposed corners of the filter box 106,110 (see Fig. 4). Such an arrangement allows the maximum surface area of the planar filter element 132a, b to be exposed to a flow of drilling mud entering the filter box 106,110 via control valve 128a, 130a.

Alternatively there may be used a'Y'type strainer (not shown) The sample chamber 114 shown in Figs. 2 and 3 is cylindrical having narrowed tapered ends at the inlet and outlet thereof.

A display screen 136 for displaying the viscosity and density measurements of a drilling mud passing through the sample chamber 114 is attached remotely to the detector device 116 by a cable 138.

A particularly suitable detector device 116 for use with the apparatus 100 of the present invention is the Solartron (trade name) type 7827 viscometer noted above which provides a display screen 136 (e. g. a Solartron 7945V) for viewing the measurements obtained by the measurement apparatus 116. The display screen 136 is also supplemented with a digital display unit (not shown) which allows viewing of the readings of the detector device 116 over distances of approximately 20 metres.

Fig. 5 shows a schematic outline of an apparatus 200 according to a second embodiment of the present invention, wherein a cylindrical sample chamber 214 has an inlet 213 at one end thereof which is raised above an outlet 222 which is located at the other end thereof such that the angle a between the longitudinal extent of the sample chamber 214 and the horizontal is about 45°.

The diaphragm pump 212 pumps drilling mud received from a pipe 205a, which is in fluid communication with a drilling mud flow circuit (not shown), to the inlet 213 of the sample chamber 214. The drilling mud flows through the sample chamber 214 past a detector device 216 which continuously measures the viscosity and density of the drilling mud and displays the measurement results on a display 236 remotely connected thereto by a cable 238.

The drilling mud passes from the sample chamber 214 to the outlet 222 and through a flow restrictor valve 224 which is used to create a back-pressure of 2 to 4 bar within the sample chamber 214. The drilling mud exits the apparatus 200 via a pipe 226 and is returned to the drilling mud flow circuit therethrough.

Similarly, in an alternative embodiment of the apparatus 200, the inlet 213 is disposed lower than the outlet 222 so that the angle a is about 60° relative to the horizontal. The apparatus 200 of Fig. 6 is not provided with a flow control valve 224.

It will of course be realised by the skilled person that variations in the configuration and choice of components are possible such as for example, the choice of pump or measurement device, and it is intended that the present invention extend to these variations.