Boring or penetrating the earth – Automatic control – In response to drilling fluid circulation
Reexamination Certificate
1998-11-20
2001-07-10
Will, Thomas B. (Department: 3671)
Boring or penetrating the earth
Automatic control
In response to drilling fluid circulation
C175S048000
Reexamination Certificate
active
06257354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to oil well drilling systems and more particularly to a drilling fluid flow monitoring and control system for use during drilling of wellbores.
2. Description of the Related Art
Oilfield wellbores are formed by rotating a drill bit carried at an end of a drill string. The drill string is comprised of a tubing which may be drill pipe made of jointed sections or a continuous coiled tubing and a drilling assembly that has a drill bit at its bottom end. The drilling assembly is attached to the bottom end of the tubing. To drill a wellbore, the drill bit is rotated by a mud motor carried by the drilling assembly and/or by rotating the drill pipe. A drilling fluid, also referred to as the “mud,” is pumped under pressure from a source at the surface (mud pit) through the tubing. The mud serves a variety of purposes. It is designed to provide the hydrostatic pressure that is greater than the formation pressure to avoid blow outs. The mud drives the drilling motor (when used) and it also provides lubrication to various elements of the drill string. Commonly used drilling fluids are either waterbased or oil-based fluids. They also contain a variety of additives which provide desired viscosity, lubricating characteristics, heat, anti-corrosion and other performance characteristics.
The mud discharges at the bottom of the drill bit and returns to the surface via the annular space between the tubing and the wellbore inside (also referred to herein as the “annulus”). One of the primary functions of the drilling fluid is the control of the formation pressure. The hydrostatic pressure exerted by the mud column is the primary method of controlling the pressure of the formation. Whenever the formation pressure exceeds the pressure exerted by the fluid column, formation fluid enters the wellbore, causing a “kick.” For the purpose of this invention, a kick is defined as any unscheduled entry of formation fluid into the wellbore. Early detection of kicks and prompt initiation of control procedures are keys to successful well control. If a kick is not detected early enough or controlled properly when detected, a blowout can occur. One method to determine the presence of a kick is to accurately determine the amount of the drilling fluid being supplied to the drill string and the amount of the fluid returning to the surface. Gain in the fluid quantity is an indicia of a kick. During the drilling of a wellbore, a certain amount of the drilling fluid is lost because it penetrates into the formation. However, excessive loss of fluid can be an indicia of wash outs.
Fluid flow measurements are made at the surface for determining the amount of the drilling fluid entering the drill string and the drilling fluid returning to the surface. Such measurements are then used to determine certain operating parameters, such as kick, fluid loss etc. There are two modes relating to the pumping of the drilling fluid into the well: (1) pumping fluid by main mud pumps through the drill string during the drilling operation, and (2) pumping fluid by a secondary into the annulus during tripping operation when the main mud pump is inactive. Fluid is pumped in the latter case to compensate for the reduction in the volume due to the removal of the drill pipe and to ensure the maintenance of the required hydrostatic pressure. A common method to determine out flow (flow rate of the returning fluid) is to install a flow sensor in a bypass line made from the main return line. Solids from the returning fluid tend to settle in the bypass line, which frequently inhibits the measurements. Electromagnetic sensors are commonly used to determine the flow of the fluids. Such sensors provide relatively accurate measurements for water-based drilling fluids. For oil-based muds, especially muds containing a relatively high percentage of oil, such sensors do not provide accurate measurements. Other commercially available sensors have not gained much use in oilfield applications because they are either prohibitively expensive or do not provide accurate measurements. The present invention addresses some of the problems with the flow measurement apparatus and methods and provides a prior art flow measurement system that provides relatively accurate measurements for any type of drilling fluid, including oil-based and water-based muds. The present invention also provides novel sensor arrangements for determining fluid flow rates.
SUMMARY OF THE INVENTION
The present invention provides a fluid flow measurement system for an oil well drilling system that includes an inflow line for supplying drilling fluid to the wellbore and pressure and a return line carrying fluid leaving the wellbore during drilling of such wellbore. The system includes at least one floating sensor assembly in the return line having a flow rate sensor that provides a measure of the velocity of the fluid in the return line. The flow rate sensor may be a thermal sensor, an electromagnetic sensor or an ultrasonic sensor. A height sensor provides the fluid level in the return line and a density sensor provides the density of the returning fluid.
The sensor assembly includes a floating carrier or vessel that carries the flow rate sensor. The assembly is mounted about a pivot point that enables the carrier to float on the fluid. A counter weight to the carrier reduces the negative affect on the measurements due to turbulence in the fluid. Multiple sensors are preferably used to improve the accuracy of the measurements.
The flow rate sensor may be a thermal sensor, an electromagnetic sensor or an ultrasonic sensor. The probe of the thermal sensor or the electromagnetic sensor remains in contact with the fluid while taking measurements. The ultrasonic sensor includes a transmitter and a receiver and a reflector. The transmitter and receiver remain above the fluid line, while the reflector remains in the fluid during the taking of the measurements.
The system includes a pump that pumps drilling fluid into the wellbore via the inflow line. A flow rate sensor in the in flow line provides the flow rate of the drilling fluid supplied to the wellbore. This sensor may be a thermal sensor, an electromagnetic sensor or an ultrasonic sensor or any other suitable sensor. The floating sensors in the system are preferably side mounted.
A controller in the system determines from the sensor measurements the flow rate of the fluid entering the wellbore, flow rate of the fluid leaving the wellbore and the mud density. The system is programmed to determine the presence of a kick and wash out from the inflow and the out flow measurements. The system also determines from the inflow a measure of the operating condition of the pump.
Additionally, the present invention utilizes flow measurement sensors to determine the amount of fluid pumped into the wellbore by a secondary pump during tripping operations while the main mud pumps are inactive. The present invention further utilizes multiple flow rate sensor in a substantially horizontal flow line between the mud pumps and the wellbore and determines therefrom the volume of the three phase mixture (liquid, gas and solids in such line).
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
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Reiber Frank
Schrader Hartmut
Baker Hughes Incorporated
Madan Mossman & Sriram PC
Petravick Meredith C.
Will Thomas B.
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