GB2516217A

GB2516217A - Rotary rheo watcher or RWW

Info

Publication number: GB2516217A
Application number: GB1310095.3A
Authority: GB
Inventors: Ross Colquhoun
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-06-05
Filing date: 2013-06-05
Publication date: 2015-01-21
Also published as: GB201310095D0

Abstract

Apparatus to monitor the rheology of a drilling fluid or mud, that is used during the drilling for oil or gas, where monitoring is conducted in a continuous and in real time. Preferably the apparatus monitors common industry measures, such as the plastic viscosity and yield point of the drilling fluid and mud via two or more viscometers which monitors the changes in the rhelogical curve of a drilling mud, by monitoring the change in the low and/or medium and/or high shear rate portions of the rheological curve (fig E) created from the results of a rotational viscometer 1 on a computer or similar device 2. The computer 2 is linked to the viscometers D1, D2, D3, that monitor mud being pumped through separate sample chambers C1, C2, C3, thereby allowing the different shear rates to be monitored. The apparatus has at least one or more sample chambers of different sizes to generate different sheer rate on the common volumetric flow. Preferably the apparatus draws a continuous sample of the mud into the sample chambers C1, C2, C3 via at least one integral or external pump. The data from the apparatus may be sent electronically to other locations.

Description

Intellectual Property Office Application No. GB1310095.3 RTTVI Date:l4November 2014 The following terms are registered trade marks and should be read as such wherever they occur in this document: Fann

ASTM

Intellectual Property Office is an operating name of the Patent Office www.ipo.govuk

Description

This invention relates to a device and system called The Rotational Rheo Watcher or RRW which continually measures S and monitors the Rheology or the Rheological properties commonly referred to as the viscosity of a Drilling Fluid commonly known as Mud which is used during the process of drilling for Oil and Gas For safe and successful Oil well drilling it is vital that the Rheology is known and correctly controlled as it functions among other things to allow well bore cleaning by transportation to the surface of rock chips or cuttings, it adds lubrication between the drill string and the well bore and thickens the mud sufficiently to hold in suspension chemicals such a barite and/or lost circulation material and/or other material used to control the mud properties.

For this document the term Rheology covers the general nature of the flow properties of a liquid and its resistance to flow and the Viscosity is used only as a general indication of the Mud's Viscosity or shear stress at a particular shear rate Commonly Mud's Rheology is so called non Newtonian as the plot of the shear rate to shear stress is not linear.

During a drilling operation, The Rheology and Viscosity is commonly measured by two methods. The first of these methods is usually performed by the rig crew and is a simple test using equipment such as a Marsh funnel and is at a single shear rate. Commonly this is a batch test made at the ambient temperature every 15 minutes or 30 minutes and is commonly referred to as The Marsh Punnel Viscosity.

The second of these methods is generally performed by a specialist such as a so called Mud Man and allows a more comprehensive understanding of the Mud's Rheology. The viscosity of the mud is recorded at different and known shear rates commonly with a rotational viscometer such as a Fann 35A VG Meter and a graph of shear rate versus shear stress can be made. Commonly the VG Meter records the shear stress at 6 different shear rates as RPM and from this testing the Rheology of the mud can be mathematically defined. It is commonly recorded as the Plastic Viscosity (PV) and Yield Point (YP) although other Rheology parameters can be calculated such as the so called low end shear and Tau zero. This is measured at a fixed and known temperature which is commonly 120 degrees Fahrenheit or approximately 50 degrees Celsius. It is a batch test performed several times a day or when required.

Of course it is recognised that other methods and instruments and number of shear rates may be used to measure the Rheology and viscosity.

Commonly the rheological properties such as the Plastic Viscosity and Yield Point are used with other parameters monitored while drilling to make calculations which are continually recorded and updated. An example of this is the so called.equivalent circulating density commonly referred to as the ECD. This is a calculation of the effective density of the circulating mud and involves many parameters such as the pump pressure and Plastic Viscosity and Yield Point and static mud density and other parameters. Some of the inputs are live and continuous while some such as the Plastic Viscosity and Yield Point are not and may be the value recorded several hours before. For safe and efficient drilling these rheological properties must also be live and continuous.

It is also recognised that the use of a VG type rotational viscometér is a commonly used item and the rheological properties measured by them are commonly used and is covered by standards such as The American Petroleum The commonly used VG type Meter is for laboratory use only and is unsuitable for installation on the circulating mud.

It is also well known that the Rotational type Viscometer is suitable for laboratory use only and is not suitable for insertion intQ circulating mud.

Other types and designs of viscometer can be suitable for field use in a so called Zone 1 installation on the circulating mud. They generally cannot repeat the commonly used values of Plastic viscosity and Yield Point and other commonly used rheological terms in a non Newtonian Fluid.

The inventor considers it vital that the values of Plastic viscosity and Yield Point and other commonly used rheological terms measured by a rotational viscometer are stil used as input into the common calculations and are taken continuously and in real time.

It is the purpose of The RRW to combine the known and commonly used results from a rotary viscometer such as the Fann 35A made in the so called safe area with viscometers that will operate in the so called Zone 1 area.

The viscometer in the RRW is of a different design and must be suitable for use with a circulating and operational mud. It must be robust, have minimal or no moving parts and be unaffected by solid objects that might be in the Mud. The inventor has found that the Tuning fork type of vibration viscometer is suitable although other types of viscometers might also be suitable.

As drilling proceeds the Rheology of a Mud changes. This can be due to several factors including so called solids build up, activation or deactivation of products due to heat or pressure or shear, or evaporation of liquid content. Of course it is understood there can be other reasons for changes to Rheology.

These changes can be shown on Fig C and Fig D. On Fig C the Mud is tested with a Rotational Viscometer and the results shown (Fig C-i) . From these results the so called Plastic Viscosity or PV and Yield Point or YP are calculated (Fig C-6) and a Rheology chart can be generated (Fig C-3). Using a so called trend-line or best fit line to the chart (Fig C-4) it can be defined mathematicaliy (Fig C-5). As drilling proceeds the Rheology of the Mud changes and this is shown on Fig D and this is illustrated by the changed PV and YP (Fig D-6) and the changed mathematical formula (Fig D-5) It is of course understood that many other Rheology curves can be found and these are just two examples to be used for illustration It is important to monitor any rheology changes continually and in so called real time. This will involve monitoring the Viscosity at 3 points on the Rheology curve as shown in Fig E (Fig E-6, Fig E-7, and Fig E-8).

Different type of Viscometers such as Tuning Fork Viscometers will monitor the Viscosity at different parts of the chart such as the so called low and medium and high shear rate regions with fig E-6 as the low shear rate, Fig E-7 as the medium shear rate and fig E-8 as the high shear rate.

Of course there may be other numbers of Viscometers used such as 4 or 5 or 6 or some such numbers each monitoring a different part of the rheological chart.

S

The Viscosity will be monitored by a different type of Viscometer such as a so called Tuning Fork' or Vibration' Viscometer which is more suitable for continuous immersion in Mud.

Of course it is realised that other types of Viscometer

may be suitable.

The RRW will monitor the Mud continually and in so called real time. Initially, the results from The Rotational viscometer (Fig B-i) will be entered into a so called PLC (Programmed logic card) on a computer or some such device (Fig B-2) and a Rheological chart will be generated (Fig D-3) and defined mathematically (Fig D-5) This PLC will be linked to the three viscometers as shown on Fig B. The Viscometers (B-Dl., B-D2, and B-D3) will be tuned in the so called low shear, medium shear and high shear regions of the chart (on Fig E).

The viscometers will monitor mud being pumped through separate so called sample chambers with the mud entering through Fig B-4 and exiting by FigB-3 to ensure a common volume of mud is processed and monitored.

As drilling proceeds this Rheology will change as the Mud changes and these changes will be monitored and measured by three of the second type viscometers at three points on the Rheology curve (Fig E-6, Fig E-7, and Fig E-8). They will focus on different parts of the chart such as the so called low shear, medium shear and high shear regions of the chart. The data generated will be transmitted back to the PLC and new Rheology Curves will be continually generated With any changes, continual and quantified new Rheology charts will be defined by the data from the second types of Viscometers which will monitor the change in Viscosity at these three separate regions of the chart and will adjust the profile of the Rheology curve. This continually changing chart on the PLC will allow particular Rheology characteristics to be calculated such as the PV, the PY, and Tau 0 and other characteristics which will also be available for external communication or so called export.

The inventor has found that the sample cylinders (B-cl, B-C2, B-C3) should be of different internal diameters to generate different shear rate from the fixed volumetric flow.

The inventor has found that the so called Plastic viscosity readings of an Oil based Mud plotted by laboratory testing are different at different sample temperatures and as a result their mathematical definition also changes. This is shown of an example on Fig F-A: As the viscosity as illustrated by the Plastic Viscosity changed with temperature compensation for temperature changes had to be made. The inventor has found that. there are commonly available formulae and compensations for viscosity change with temperature such as ASTM D341 but these are related to the behaviour of Oil only.

Oil based Mud is an emulsion of water in oil with solids and added chemicals but the inventor has substantially tested different Oil based Muds against known formulae, such as ASTM D341, and found that with modification they can be used for Oil based Mud.

This allows the use of the so called Referred Viscosity to be used to compensate for any temperature changes *in the Circulating Oil based Mud.

The inventor has also found that changes to viscosity caused by temperature changes is much less significant in so called Water based Mud and formulae such as ASTM are less useful.

The inventor has also found that it is important to have a steady volumetric flow of Mud in the RWW but a step change to a different but also steady volumetric flow of Mud in the RWW effectively changes the shear rates inside the RWW. With the changed shear rate the viscosity monitored by each viscometer is also changed in effect doubling the viscosity readings generated