WO2015005998A1

WO2015005998A1 - Well fluid treatment apparatus

Info

Publication number: WO2015005998A1
Application number: PCT/US2014/041105
Authority: WO
Inventors: Nathan R. HUTCHINGS; William J. CHILDS
Original assignee: Bear Creek Services, Llc
Priority date: 2013-07-11
Filing date: 2014-06-05
Publication date: 2015-01-15

Abstract

A system for processing fluids includes a substantially cylindrical fluid tank having a tangentially disposed fluid inlet proximate a top thereof. A fluid drain is disposed proximate a center of the fluid tank, the drain having an upper end at a selected level below the top of the fluid tank and having a discharge line connected thereto penetrating the tank. A solids collection volume is disposed at a base of the fluid tank and has a remotely operable valve coupled to a bottom thereof. At least one weight sensor is configured to measure a weight of the fluid tank, fluid in the tank and solids disposed in the solids collection volume.

Description

WELL FLUID TREATMENT APPARATUS Background

[0001] This disclosure relates generally to the field of oil and gas well intervention operations. More specifically, the disclosure relates to apparatus for treating fluids returned from a wellbore during intervention operations.

[0002] During oil and gas well interventions, fluid circulating through the well can become hazardous to personnel due to the temperature and pressure of the fluid and presence of toxic chemicals and potentially explosive hydrocarbons. In addition to hazards to personnel, machinery exposed to wellbore fluid is subject to high temperature, pressure, corrosive chemicals, and abrasive debris including sand found in the fluid stream. In some procedures involving oil or gas wells including drilling, clean out, and plug removal; drilling rigs or coiled-tubing units are used to enter the well and remove debris from the wellbore. Intervention apparatus such as drilling rigs and coiled-tubing units require high pressure pumps to circulate fluid through drill pipe or tubing, through a bottom-hole assembly, and back to the surface through the annulus between the drill pipe or tubing and the casing or wall of the well. The fluid returning to surface is often high temperature, high pressure, and contaminated with hydrocarbons and/or corrosive chemicals. In addition, solids returning to surface may be abrasive and damage anything in the flow path.

Summary

[0003] A system for processing fluids according to one aspect includes a substantially cylindrical fluid tank having a tangentially disposed fluid inlet proximate a top thereof. A fluid drain is disposed proximate a center of the fluid tank, the drain having an upper end at a selected level below the top of the fluid tank and having a discharge line connected thereto penetrating the tank. A solids collection volume is disposed at a base of the fluid tank and has a remotely operable valve coupled to a bottom thereof. At least one weight sensor is configured to measure a weight of the fluid tank, fluid in the tank and solids disposed in the solids collection volume. Brief Description of the Drawings

[0004] FIG. 1 shows an example well intervention operation such as wellbore drilling.

[0005] FIG. 2 is a side view of an example fluid treatment apparatus.

[0006] FIG. 3 is a top view of the example apparatus shown in FIG. 2.

Detailed Description

[0007] An example of a drilling system drilling a wellbore through subsurface rock formations is shown schematically in FIG. 1. The drilling system shown in FIG. 1 is only meant to serve as an example of a drilling system for purposes of explaining devices that may ultimately be placed on a mobile offshore drilling unit for processing drilling fluid returning from such a wellbore as a result of drilling and related operations as will be explained with reference to FIGS. 3 through 7. The example drilling system shown in FIG. 1 is not a limit on the scope of the present disclosure, nor is the present disclosure limited to wellbore intervention such as drilling. FIG. 1 and the accompanying description is provided only for the purpose of showing an example of fluid being pumped into a wellbore and being returned therefrom with included contaminants therein.

[0008] The drilling system 100 may include a hoisting device known as a drilling rig 102 that is used to support drilling operations through subsurface rock formations such as shown at 104. Many of the components used on the drilling rig 102, such as a Kelly (or top drive), power tongs, slips, draw works and other equipment are not shown for clarity of the illustration. A wellbore 106 is shown being drilled through the rock formations 104. As will be further explained below, such formations may be below the bottom of a body of water. A drill string 112 is suspended from the drilling rig 102 and extends into a wellbore 106, thereby forming an annular space (annulus) 115 between the wellbore wall and the drill string 112, and/or between a casing 101 (when included in the wellbore 106) and the drill string 112. One of the functions of the drill string 112 is to convey a drilling fluid 150 (shown in a storage tank or pit 136) to the bottom of the wellbore 106 and into the wellbore annulus 115. [0009] The drill string 112 may support a bottom hole assembly ("BHA") 113 proximate the lower end thereof that includes a drill bit 120, and may include an hydraulically operated "mud" motor 118, a sensor package 119, and a check valve (not shown) to prevent backflow of drilling fluid from the annulus 115 into the drill string 112. The sensor package 119 may be, for example, a measurement while drilling and logging while drilling (MWD/LWD) sensor system. The BHA 113 shown in FIG. 1 may also include a telemetry transmitter 122 that can be used to transmit pressure measurements made by the transducer 116, MWD/LWD measurements as well as drilling information to be received at the surface. A data memory including a pressure data memory may be provided at a convenient place in the BHA 113 for temporary storage of measured pressure and other data (e.g., MWD/LWD data) before transmission of the data using the telemetry transmitter 122. The telemetry transmitter 122 may be, for example, a controllable valve that modulates flow of the drilling fluid through the drill string 112 to create pressure variations detectable at the surface. The pressure variations may be coded to represent signals from the MWD/LWD system and the pressure transducer 116.

[0010] The drilling fluid 150 may be stored in a reservoir 136, which is shown in the form of a mud tank or pit. The reservoir 136 is in fluid communications with the intake of one or more mud pumps 138 that in operation pump the drilling fluid 150 through a conduit 140. An optional flow meter 152 may be provided in series with one or more mud pumps 138, either upstream or downstream thereof. The conduit 140 is connected to suitable pressure sealed swivels (not shown) coupled to the uppermost segment ("joint") of the drill string 112. During operation, the drilling fluid 150 is lifted from the reservoir 136 by the pumps 138, is pumped through the drill string 112 and the BHA 113 and exits the through nozzles or courses (not shown) in the drill bit 120, where it circulates the cuttings away from the bit 120 and returns them to the surface through the annulus 115. The drilling fluid 150 returns to the surface and goes through a drilling fluid discharge conduit 124 and optionally through various surge tanks and telemetry systems (not shown) to be returned, ultimately, to the reservoir 136.

[0011] A pressure isolating seal for the annulus 115 may be provided in the form of a rotating control head forming part of a blowout preventer ("BOP") 142. The drill string 112 passes through the BOP 142 and its associated rotating control head. When actuated, the rotating control head on the BOP 142 seals around the drill string 112, isolating the fluid pressure below the BOP 142, but still enables drill string rotation and longitudinal movement. Alternatively a rotating BOP (not shown) may be used for essentially the same purpose.

[0012] As the drilling fluid 150 returns to the surface it may pass through a side outlet below the pressure isolating seal (rotating control head or BOP 142) to the fluid discharge conduit 124. The drilling fluid 150 exits the fluid discharge conduit 124 and may be directed to a degasser, such as a vacuum or centrifugal degasser 17, and then to in an inlet 12 of a fluid treatment apparatus, shown generally at 50, and designed to remove gas, solids and other contaminants, including drill cuttings, from the drilling fluid 150. After passing through a fluid treatment apparatus to be explained further below, the drilling fluid 150 may be returned to the reservoir 136.

[0013] Referring to FIG. 2, an example well fluid treatment apparatus 50 is shown. The apparatus 50 may consist of a cylinder 10 of a selected diameter and height. The present example may be 42 inches in diameter and 30 inches tall, although such dimensions are not a limit on the scope of the present disclosure. The cylinder 10 may have a partially open top and a cone 10A affixed to and starting at the base of the cylinder 10, and extending a selected distance, in the present example 24 inches, below the bottom of the cylinder 10. A remotely operable valve 24 may be located at the base of the cone 10A. Fluid returning from a wellbore (e.g., through a conduit 124 as explained with reference to FIG. 1) enters the cylinder 10 through an inlet 12 near the top of the cylinder 10. The inlet 12 is disposed at an angle such that it is substantially tangential to the wall of the cylinder 10. The tangential orientation of the fluid inlet 12 causes a cyclonic flow of the fluid around the interior of the cylinder 10. The top of the cylinder 10 is partially open to expose the fluid to the atmosphere.

[0014] Referring to FIG. 3, a striking plate 13A is located in the flow path to break up the flow and aerate the fluid. The striking plate 13A may form part of a cover plate 13 that is disposed on part of the top of the cylinder 10. A weir 16, which may be in the form of a cylinder open at least at its bottom end (see FIG. 2), may be attached to the cover plate 13.

[0015] Returning once again to FIG. 2, a drain 18, which in the present example may be

6 inches in diameter, may be located in the center of the cylinder 10. Center is meant herein as the center of the cyclonic fluid flow. The drain 18 and cylinder 10 make up a pipe within a pipe. The drain 18 may be connected to and sealingly pass through a side wall of the cylinder 10 through a fluid discharge pipe 14. The drain 18 may be isolated from the cyclonic flow by the weir 16. The drain 18 does not extend to the top of the cylinder 10, but may be located a selected distance, in the present example approximately 25 inches, from the top of the cylinder 10. The cyclonic flow of the fluid forces debris toward the wall of the cylinder 10 and away from the drain 18, which is in the center of the cyclonic flow. Debris in the form of solids, which are more dense than the fluid, sinks into the cone 10A where the debris may rest next to the valve 24. The valve 24 may be opened automatically, as described below, to dump the debris from the cone 10A through a discharge line 26 to a holding tank or other storage device (not shown). In order for the valve 24 to not foul on trapped debris, a pneumatic pinch valve may be used as the valve 24, though other kinds of valves may be used in other implementations. The valve 24 may be operated by an actuator 24A of a type consistent with the type of valve used.

[0016] Automatic operation of the valve 24 may be performed by measuring the weight of the entire system, i.e., the cylinder 10, cone 10A, discharge lines 14, 26, drain 18 and weir 16, and comparing it to the weight of the system filled with an equal volume of a known density fluid. The weight may be measured using load cells 20, e.g., coupled to an exterior of the cylinder 10. As described below, the level of fluid in the system may be determined by the fluid flow rate into the cylinder 10. Therefore, to ensure solids are dumped and not fluid, the level of fluid in the system may be measured. The fluid level may be measured using a level sensor 22, non limiting examples of which include a radar sensor, capacitance sensor or acoustic travel time sensor. The measured fluid level corresponds to an expected weight of the system where the expected weight is the weight of the apparatus 50 plus a volume of a known density fluid. The weight expected at a given fluid level and known fluid density is compared to the total weight of the system (i.e., the apparatus plus fluid and debris). In the present example Wheatstone bridge load cells may be used. The level of fluid and total weight of the system (system comprising the apparatus 50, fluid and debris) may be monitored by a controller 30, which may be, for example and without limitation, any microprocessor, computer or other programmable controller such as a programmable logic controller (PLC). The controller 30 monitors the weight of the system compared to the weight of the system previously determined with a known fluid. As solid debris fills the cone 10A, the total weight measured by the load cells 20 eventually may exceed the expected weight programmed into the controller 30. The controller 30 may be programed to allow the measured weight to exceed the expected weight by a predetermined amount. When the predetermined amount is exceeded, the controller 30 may send a signal to the valve actuator 24 A to open the valve 24 at the base of the cone 10A until the total measured weight is within a predetermined value of the expected weight. In this way, solids may drop out of the bottom of the cone 10A into a holding tank or other storage device (not shown). Fluid may be discharged from the discharge line 14, and, as in the example shown in FIG. 1, may be returned to a reservoir (136 in FIG. 1) or other tank. While monitoring the fluid level and comparing the expected weight to the measured weight may be a robust method of dumping solids while minimizing fluid dumping, it is possible to program the controller 30 to operate the valve 24 and dump solids when a predetermined weight is measured by the load cells 20 without input from the level sensor 22. This operating sequence may be performed if the flow rate into the cylinder 10 is known and does not vary excessively. In this way, the expected weight of the system (weight without debris) should not substantially change, and the additional weight as measured by the load cells 20 may be assumed to result only from solids accumulation. Alternatively, if the solids reservoir (i.e., the cone 10A) is sufficiently large such that the weight of solids can accumulate to substantially change the weight of the system (i.e., solids, liquid and the apparatus), the level sensor 22 may not be needed as the measured weight required to result in operation of the valve 24 could only be reached if the solids reservoir (cone 10A) were sufficiently laden with debris. In other examples, some level sensors may be used to monitor both the fluid level and solids level. Some kinds of guided-wave radar sensors are able to measure solids levels in a fluid medium. Use of such a sensor as the level sensor 22 could enable automatic operation of the valve 24 when the solids exceed a predetermined level in the cone 10A.

[0018] Quantification of the debris extracted from the fluid flow may be performed by monitoring the number of valve operation cycles initialed by the controller 30. Because the controller 30 may be programmed to operate the valve 24 when a certain amount of debris is present (e.g., as measured by system weight or solids level) and remains open until a certain amount of debris remains (which may be zero, again as may be determined by solids level or system weight), each valve operation or "dump" deposits a substantially consistent amount, by weight or volume, of debris. Counting the number of "dumps" may enable determining the total amount of debris extracted from the returning fluid flow by the system. Also, the load cells 20 and level sensor 22 measurements may be recorded by the controller 30 throughout an entire intervention operation, or may be recorded with a separate data recorder (not shown), such that later analysis may enable determining when the dumps occurred and exactly how much weight was lost to the system in each dump. The foregoing may enable a detailed analysis of exactly how much debris was recovered and at what times during the intervention operations the debris was recovered.

[0019] Flow rate through the system may be determined by monitoring the level sensor

22. Fluid must accumulate in the cylinder 10 until the level of fluid is higher than the drain 18 before the fluid can exit the cylinder 10 through the fluid discharge line 14. The rate of fluid exiting the cylinder corresponds to the differential pressure between the drain 18 and the fluid discharge line 14. To increase the differential pressure, fluid height above the drain 18 may be increased. If fluid enters the cylinder 10 at a particular rate, the level of fluid in the cylinder 10 will change until the differential pressure driving the fluid discharge reaches a value where the fluid discharge rate equals the fluid input rate. Therefore, a given flow rate into the cylinder will correspond to a fluid level in the cylinder 10 that produces the same flow rate out of the cylinder 10. The level-flow rate relationship can be determined empirically, e.g., by calibration prior to use of the system. Once a fluid level - flow rate calibration for a number of different density fluids has been determined, monitoring the fluid level in the system leads directly to monitoring the system flow rate if the density of the fluid entering the inlet 12 is known or can be determined. While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

Claims What is claimed is:

1. A system for processing fluids, comprising:

a substantially cylindrical fluid tank having a tangentially disposed fluid inlet proximate a top thereof;

a fluid drain proximate a center of the fluid tank, the drain having an upper end at a selected level below the top of the fluid tank and having a discharge line connected thereto penetrating the tank;

a solids collection volume disposed at a base of the fluid tank and having a remotely operable valve coupled to a bottom thereof; and

at least one weight sensor configured to measure a weight of the fluid tank, fluid in the tank and solids disposed in the solids collection volume.

2. The system of claim 1 further comprising a weir disposed between the drain and a wall of the fluid tank.

3. The system of claim 1 further comprising a controller in signal communication with the at least one weight sensor, the controller programmed and configured to open the valve when a first selected weight is measured.

4. The system of claim 3 wherein the controller is programmed to close the valve when the measured weight drops to a second selected weight.

5. The system of claim 3 further comprising at least one fluid level sensor in signal communication with the controller, the controller programmed to determine the selected weight based on signal input from the level sensor.

6. The system of claim 5 wherein a flow rate out of the fluid tank is calibrated to a fluid level measured in the tank by the at least one fluid level sensor.

7. The system of claim 5 wherein the at least one fluid level sensor comprises at least one of a guided wave radar sensor, a capacitance sensor and an acoustic travel time sensor.

8. The system of claim 7 wherein the fluid level sensor comprises a guided wave radar sensor, the fluid level sensor providing signals to the controller indicative of both fluid level in the tank and solids level in the collection volume.

9. The system of claim 8 wherein the controller is programmed to operate the valve when the solids level reaches a selected value.

10. A method for treating fluid, comprising:

introducing fluid into a substantially cylindrical tank proximate an upper end thereof at a tangential direction to induce cyclonic motion of the fluid in the tank; draining fluid from the tank proximate a center thereof, the draining performed at a selected distance below the top of the tank;

collecting solids in a selected volume below the tank separated by the cyclonic motion of the fluid in the tank; and

automatically releasing the collected solids when at least one of a predetermined weight of the tank, solids collection volume, fluid and collected solids is reached, a predetermined measured level of solids is reached and a predetermined level of fluid and the predetermined weight are reached.

11. The method of claim 10 further comprising measuring a fluid level in the tank and determining a fluid flow rate through the tank based on a predetermined calibration of fluid level in the tank with respect to flow rate.

12. The method of claim 10 further comprising quantifying an amount of the collected solids by counting a number of and duration of the automatic release of the collected solids.