Method of measuring quality of steam in a flow fine

A method for determining the quality of steam flowing in a line used for steam injection, e.g. in an oil well. It has a vertical loop in the line, with an orifice in the up-flow side. The pressure, temperature and pressure drop at the orifice are measured before and after injecting a stream of water upstream from the orifice. The water stream is injected at a constant flow rate, and its temperature and pressure are measured. Using the measurements before and after the introduction of the water stream, simultaneous equations are developed related to the mass flow rate and to the heat flow rate, so that the steam quality may be determined.

FIELD OF THE INVENTION 
This invention concerns a method for measuring quality of a gaseous fluid 
mixture that includes an unknown quantity of a liquid component. More 
specifically, it is concerned with a method for measuring the quality of 
steam in a flow line to an injection well in a steam flooding project for 
oil recovery. 
BACKGROUND OF THE INVENTION 
With the advent of steam flooding projects, i.e. in oil recovery from oil 
fields that need stimulation to produce the oil, there is a need for a 
simple method to determine the quality of steam at the well head of an 
injection well. Such a measurement would be particularly useful to 
determine the heat input to the underground reservoir. The measurement is 
important because steam quality directly affects production operations, 
earnings and future investment requirements. In the past, the desired 
information was not obtainable after a steam supply had been split by use 
of a manifold which separated the liquid and vapor components of the 
steam. However, by use of a method according to this invention, the 
quality measurements may be directly made individually for steam lines 
supplying each injection well. 
BRIEF SUMMARY OF THE INVENTION 
Briefly, the invention concerns a method of measuring the quality of a 
gaseous fluid mixture having an unknown quantity of a liquid component. It 
comprises the steps of passing said fluid mixture through an orifice, and 
measuring the pressure, the differential pressure and the temperature at 
said orifice of said fluid mixture. It also comprises the step of 
injecting a known quantity of said liquid component at a known temperature 
and pressure into said fluid mixture upstream of said orifice. And it 
comprises the steps of measuring the pressure, the differential pressure 
and the temperature at said orifice again, after said step of injecting, 
whereby said quality may be calculated. 
Again briefly, the invention is in a steam injection procedure for 
recovering oil by introducing steam into one or more injection wells. It 
concerns a method of accurately determining the quality of steam being 
injected through a flow line, and it comprises the steps of introducing an 
orifice into said flow line, and measuring the static pressure the 
temperature and the pressure drop across said orifice. It also comprises 
the steps of injecting a quantity of water upstream from said orifice, and 
measuring the temperature the pressure and the mass flow of said quantity 
of water. It also comprises the steps of measuring the static pressure, 
the temperature, and the pressure drop across said orifice after said 
injecting of water upstream from said orifice, and determining the quality 
of steam being injected by solving simultaneous equations derived from 
said measurements before and after said water injection. 
Once more briefly, the invention is in a steam injection procedure for 
recovering oil by introducing steam into one or more injection wells. It 
comprises a method of accurately determining the quality of steam being 
injected through a flow line to one of said injection wells, which 
comprises the steps of providing a vertical loop in said flow line for 
creating uniformity in cross section flow. It also comprises the steps of 
introducing an orifice into said flow line in the up-flow side of said 
loop at a point of uniform cross section flow, and measuring the static 
pressure the temperature and the temperature drop across said orifice. It 
also comprises the steps of injecting a stream of water at a constant rate 
upstream from said orifice and measuring the temperature the pressure and 
the liquid mass flow of said injected stream of water. It also comprises 
the steps of measuring the static pressure the temperature and the 
pressure drop across said orifice after steady state conditions following 
said injecting a stream of water at a constant rate, and determining the 
quality of steam being injected by solving simultaneous equations derived 
from mass flow rates and heat flow rates using Newton's Method.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As indicated above, there has been a problem in steam flooding projects 
where steam is injected into oil wells, in order to stimulate the recovery 
of additional oil by the heating effects of the steam. It has not been 
feasible to determine steam quality at each individual injection well 
head. However, such knowledge is important because the steam quality 
directly effects the production operations and consequently the earnings 
and future investment requirements for steam flooding projects. 
A method according to this invention provides for a simple and effective 
procedure that permits measurement of the steam quality in a flow line 
just prior to the introduction into a given injection well. An 
illustration of typical apparatus that may be employed to carry out the 
method is illustrated in the FIGURE of Drawings. As there illustrated, the 
steam injection procedure is used for recovering oil by introducing steam 
into an injection well 11. The well 11 has a well head 12 into which there 
is a pipe 13 connected. Also, there will be a valve 16 for controlling 
flow to or from the well 11. 
In connection with a method according to this invention the pipe 13 has 
heat insulation which covers a steam flow line 17 through which the steam 
that is to be injected for the well stimulation procedure passes. The 
steam flow line 17 is illustrated somewhat enlarged and is schematically 
shown partially in longitudinal cross section on the left hand side of the 
drawing. This is in order to illustrate the fact that there is a vertical 
loop 20 in the flow line 17. Loop 20 provides a means for having the steam 
flow (particularly on the upflow side of the loop) develop a uniform flow 
pattern in cross section. 
As indicated above, the pipe 13 that includes the steam flow line 17 is 
heat insulated. Thus, the steam flow line 17 is covered with a heat 
insulating layer 21 in order to minimize heat loss as the steam flows 
through the line. On the upflow side of the loop 20 there is a orifice 24 
which is used in connection with making measurements that are used as the 
method is carried out. It will be understood that the orifice 24 may be 
formed by inserting a plate 23 or similar barrier, diametrically across 
the flow line 17. The plate 23 has a central opening or orifice 24 
therein. It may be noted that there is a schematic indication of the 
measurements that are taken at the orfice 24. They are indicated in a 
circle 25 which has the letters P, .DELTA.P and T inside. These indicate 
the measurements of static pressure, differential pressure and 
temperature, respectively. 
Upstream from the orifice 24 there is a small pipe 28 that connects into 
the flow line 17. This is for introducing or injecting a stream of water 
during part of the procedure. In order for the injected flow of water to 
be at a constant rate, there is a pump 29 which draws its source of water 
from a water tank 30. When the water is being injected the measurements 
that are taken include the temperature, the pressure and the mass flow of 
the injected water. These measurements are schematically indicated by the 
symbols in a circuit 33 namely T.sub.i, P.sub.i and m.sub.i. 
It is known that by use of an orifice meter the quality of steam in a flow 
line can be determined if the mass flow rate is known. Also, if the 
quality is known the mass flow rate can likewise be determined. However, 
if both of the mass flow rate and the steam quality are unknown (which is 
frequently the case where a steam project has a steam supply provided 
through a manifold and then connected to various wells for injection), the 
orifice meter equation can not be solved. However, in accordance with our 
invention, a method involving use of an orifice in combination with 
injection of liquid makes it possible to determine both the quality and 
the mass flow rate of steam in a flow line. Such a method involves the 
following four steps. 
1. Make a standard measurement of pressure, temperature and differential 
pressure across an orifice. 
2. Upstream of the orifice, inject a liquid at known temperature, pressure 
and rate of flow. 
3. Make measurements of pressure, temperature and differential pressure 
once steady state condition has been achieved after the liquid injection 
is underway. 
4. Solve the orifice equation at two different conditions simulataneously 
for original quality and original mass flow rate. 
A specific example of carrying out the method is described hereafter with 
reference to the schematic illustration of the drawing. 
An insulated steam flow line 17 has an unknown quality steam flow 
proceeding therethrough in the direction of the arrows. It goes to the 
well 11 for injection in order to carryout a stimulation procedure. It 
will be noted that the illustration shows a layer of insulation 21 for 
providing heat insulation around the steam flow line 17. 
At the orifice 24 the differential pressure (.DELTA.P) and the pressure (P) 
as well as the temperature (T) of the flowing steam are measured. Upstream 
of the vertical pipe loop 20 there is an injection port 35 formed at the 
end of the pipe 28. At this point, water is injected into the flowing 
steam at a measured temperature T.sub.i and pressure P.sub.i as well as a 
mass flow rate m.sub.i are measured. The pump 29 acts to inject the water 
from the storage tank 30 through the injection port 35 at the end of the 
pipe 28 into the flow line 17 at a constant rate. 
The method may be explained in general mathematical form in accordance with 
the following. An orifice plate correlation may be written which expresses 
the relationship of steam quality to mass flow rate. However, such 
expression is only one equation and there are two unknowns: 
EQU X.sub.1 =f.sub.1 (m.sub.1) (1) 
Where: m.sub.1 =mass flow rate of steam at initial conditions, 
X.sub.1 =steam quality at initial conditions and 
f.sub.1 =an empirical correlation function. 
A second equation can be obtained by injecting liquid (water) into the 
two/phase gas-and-liquid (steam) to obtain a new equation as follows: 
EQU X.sub.2 =f.sub.2 (m.sub.2) (2) 
Where: m.sub.2 =mass flow rate of steam after injection of water started, 
X.sub.2 =steam quality after injection of water started, and 
f.sub.2 =a different or the same empirical correlation function. 
In accordance with the foregoing it follows that the following equation 
expresses the mass flow rates involved: 
EQU m.sub.2 =m.sub.1 +m.sub.1 (3) 
Where m.sub.i =the measured injected mass flow rate of the liquid (water). 
The heat flow rate at initial conditions may be expressed by the following 
equation: 
EQU q.sub.1 =m.sub.1 (h.sub.fg1 X.sub.1 +h.sub.f1) (4) 
Where q.sub.1 =heat flow at initial conditions. 
h.sub.fg1 =latent heat of vaporization of water at initial conditions, and 
h.sub.f1 =sensible heat content of water at initial conditions. 
The heat flow rate after constant water injection is started, may be 
expressed as: 
EQU q.sub.2 =m.sub.2 (h.sub.fg2 X.sub.2 +h.sub.f2) (5) 
Where q.sub.2 =heat flow rate after constant water injection is started, 
h.sub.fg2 =latent heat of vaporization of water after constant water 
injection started, and 
h.sub.f2 =sensible heat content of water after constant water injection 
started. 
Then, assuming negligible change in heat loss between the injection port 
(the water) and the orifice plate, the heat flow rate may be expressed as: 
EQU q.sub.2 =m.sub.1 (h.sub.fg1 X.sub.1 +h.sub.f1)+m.sub.1 h.sub.fi (6) 
Where: h.sub.fi =sensible heat content of injected water. Then equations 
(3), (5) and (6) can be combined to express X.sub.2 in terms of X.sub.1 as 
follows: 
EQU m.sub.1 (X.sub.1 h.sub.fg1 +h.sub.f1)+m.sub.i h.sub.fi =(m.sub.1 
+m.sub.i)(X.sub.2 h.sub.fg2 +h.sub.f2) (7) 
Since equations (3) and (7) express m.sub.2 and X.sub.2 in terms of m.sub.1 
and X.sub.1, there are two equations and two unknowns (m.sub.1 and 
X.sub.1). However, these simultaneous equations may be solved using 
Newton's Method. 
The method steps that are involved in the invention may be described in the 
following manner which is related to a steam injection procedure for 
recovering oil by introducing steam into one or more injection wells. The 
method is used for accurately determining the quality of steam that is 
being injected through a flow line to one of the injection wells, and it 
comprises the following steps. 
(1) Providing a verticle loop in the flow line, e.g. the loop 20 
illustrated in the drawing. This verticle loop is effective in creating 
uniformity of the cross section flow of the steam that is passing through 
the flow line. 
(2) Introducing an orifice into the flow line in the up flow of the loop, 
at a point of uniform cross section flow. This is accomplished by the 
introduction of the plate 23 with orifice 24, that is spaced somewhat 
above the curve from the horizontal portion of flow line 17 to the up flow 
leg of the loop 20. 
(3) Measuring the static pressure, the temperature and the pressure drop 
across the orifice. This step is carried out by conventional measuring 
instruments to determine the indicated static pressure and the pressure 
drop, as well as the temperature at the location of the orifice. 
(4) A next step is that of injecting a stream of water at a constant rate 
upstream from the orifice. It will be understood that this injection of a 
water stream is carried out using the pump 29 to deliver a stream of water 
through the pipe 28 which is located in the stream flow line 17 on the up 
stream side of the loop 20. The flow of water will be regulated to have a 
constant rate. 
(5) A next step is that of measuring the temperature, the pressure and the 
liquid mass flow of the injected stream of water. It will be understood 
that the temperature and the pressure measurements may be done with 
conventional instruments. Also, because the liquid mass flow of the water 
stream is directly related to the amount of water flowing (since it is an 
incompressible fluid) a conventional, rate of flow, meter will accomplish 
the necessary measurement. 
(6) A next step is that of measuring the static pressure, the temperature 
and the pressure drop across the orifice after steady state conditions 
following the injection of the water stream at a constant rate. In this 
case, the same instruments will be employed to make the measurements under 
the changed conditions. 
(7) A final step is that of determining the quality of steam being 
injected. The determination is accomplished by solving simultaneous 
equations that are derived from the mass flow rates and the heat flow 
rates involved in the two different flow conditions. Such simultaneous 
equations are solved using Newton's Method. It will be appreciated by any 
one skilled in the art that the step of solving simultaneous equations 
using Newton's Method will be greatly facilitated by making use of a 
computer type of calculator in order to carry out the iterative steps for 
arriving at a solution. 
While a particular embodiment of the invention has been described above in 
considerable detail in accordance with the applicable statues, that is not 
to be taken as in any way limiting the invention but merely as being 
descriptive thereof.