Abstract:
The present invention relates to an extraction, analysis and measuring method and system intended for constituents carried along by a well fluid during drilling operations. The system comprises in combination: draw-off means ( 4 ) for taking a volume of the fluid, extraction means ( 3 ) for extracting in vapour form the constituents contained in the fluid, comprising a space placed under underpressure, a transport line ( 14 ), sampling means ( 27 ) comprising a sampling loop allowing to take a determined amount of the vapors circulating in the line, distribution means ( 40 ) that inject the amount into analysis and measuring means ( 31 ), control means ( 33 ) for controlling the temperature of the sampling means so as to prevent condensation of said amount of vapors.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and to a system intended for analysis and measurement of liquid or gaseous constituents contained in a drilling fluid. The term constituents designates here hydrocarbons, for example C1 to C8, including benzene, toluene, xylene, or gases such as H 2 S, CO 2 , O 2 , H 2 , N 2 . These constituents are due to drilling operations carried out through formation layers, operations that have the effect of breaking the rock, thereby releasing the gases or the fluids contained in the rock pores. Drilling is conventionally carried out with a circulation of a fluid referred to as drilling fluid whose function, among others, is to clean the drill bit and to drive the rock debris up to the ground surface. The constituents in question are therefore also carried along to the surface by means of this carrier. It is clear that, considering the flow rate of the drilling fluid compared to the rate of destruction of the rock, the volume amount of said constituents is always relatively low compared to the volume of mud. 
     BACKGROUND OF THE INVENTION 
     There are known installations allowing to carry out qualitative and quantitative measurements of the C1-C5 gas contained in a drilling fluid, measurements (or logging operations) allowing to identify the geologic zones drilled for borehole and/or staff safety reasons. Document FR-2,646,508 describes a process and a device for continuous sampling of gaseous samples contained in a solid-containing liquid, notably a drilling fluid. In this document, neither its degassing mode nor its transportation mode allows to extract and to transport the hydrocarbons possibly present in liquid form in the mud carried along to the ground surface. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to implement the conditions required for: extraction of gaseous or liquid constituents contained in a drilling fluid, transportation of these constituents in gaseous form, and analyses and measurements of these constituents. In order to carry out correct analyses, allowing to better determine the nature and the composition of the formations crossed by a borehole, the constituents must not condense in the elements of the system and the time of transit of these constituents between the point of extraction and the point of measurement must be acceptable to allow the drilling operation to be monitored. 
     The present invention thus relates to an extraction, analysis and measuring system intended for constituents carried along by a well fluid during drilling operations. The system comprises in combination: 
     draw-off means for taking a determined volume of the fluid, 
     extraction means for extracting, in vapour form, the constituents contained in the volume of fluid, comprising a space placed under underpressure, 
     a vapour transport line, a first end of which communicates with the space, the second end being connected to a vacuum pump, 
     sampling means placed in the vicinity of the second end, comprising a sampling loop that allows to sample a determined amount of the vapours circulating in said line, 
     distribution means that inject the amount into analysis and measuring means, and 
     means for controlling the temperature of the sampling means so as to prevent condensation of the amount of vapours. 
     The space that contains the drilling fluid drawn off can be sealed against the outer environment. 
     The space can comprise an inlet port for an auxiliary gas, air or nitrogen for example. 
     The extraction means can comprise means for heating said volume of fluid sampled. 
     The sampling loop can be mounted directly in parallel on the transport line. 
     The drilling fluid draw-off means can comprise a suction pump and/or a discharge pump. 
     The space can be at an absolute pressure ranging between 10 and 100 mb, and the suction of the vacuum pump can range between 1 and 10 mb. 
     The invention also relates to an extraction, analysis and measuring method intended for constituents carried along by a well fluid during drilling operations, wherein the following stages are carried out: 
     a volume of drilling fluid is drawn off and placed in a space belonging to extraction means intended for extraction of constituents in vapour form, 
     an underpressure is applied in the space by means of a line connecting the analysis and measuring means to the extraction means, 
     a determined amount of the vapours circulating in the line is drawn off in the vicinity of the analysis and measuring means, 
     the amount of vapours is injected into the analysis and measuring means, 
     the nature and/or the amount of the constituents vaporized in the extraction means is deduced. 
     According to the method, the underpressure and/or temperature conditions can be adjusted for extraction in vapour form as a function of the drilling parameters, for example the nature of the fluid, the flow rate, the ambient temperature, the time of transit in the line. 
     A feed flow rate of the auxiliary gas fed into the space can be adjusted. 
     An underpressure ranging between 10 and 100 mb in absolute pressure can be applied in the extraction space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will be clear from reading the description hereafter of a non limitative embodiment example, with reference to the accompanying drawings wherein: 
     FIG. 1 is an overall view of the system according to the invention, 
     FIGS. 2 a  and  2   b  show the sampling device according to the prior art intended for analysis and measurement of the constituents in a chromatograph, 
     FIGS. 3 a  and  3   b  show the sampling device according to the invention intended for analysis and measurement of the constituents in a chromatograph under the present conditions. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1, reference number  1  designates a flowline through which flows drilling fluid  2  returning from the well bottom by circulating in the annulus defmed by the drill string and the wellbore. This flowline  1  leads the drilling fluid from the wellhead to the surface installation for treatment and separation of the solids. Extraction means  3  intended for the constituents to be analyzed preferably comprise a pump  4  whose inlet  5  plunges into the drilling fluid and whose discharge end opens into a vessel  6  whose volume allows to hold as a buffer a determined volume of fluid for a given time, said time depending on this volume and on the flow rate of pump  4 . The volume of drilling fluid contained in vessel  6  is subjected to stirring in order to favour extraction through degassing and evaporation. This stirring operation can be mechanical, for example, by means of a rotating agitator  7 , or ultrasonic means. 
     In order to obtain the desired extraction conditions, heating means  8  can comprise a heating rod  9  inside vessel  6 ,an electric power supply  10  and a control and regulation line  11 . Other means for heating the volume of fluid in the vessel can be used, for example from outside, or a double heating wall. The vessel also comprises a mud discharge line  12  intended for the fluid flow taken by the pump and returning to the flowline. It is possible to place a pump  13  on this discharge line so as to better control the rate of circulation of the drilling fluid retained in vessel  6 . 
     A line  14  connects extraction means  3  to analysis and measuring means  20 . The length of this line can range between 50 and 200 m since measuring means  20  are placed in a cab (symbolized by frame  15 ) located at a sufficient distance from the wellhead to be in a secure zone. At the end of this line, a vacuum pump  21  creates an underpressure that can reach several millibars (1 to 10 mb for example). Considering the pressure drops and the circulating gas flow, the underpressure at the inlet  22  of the line can range for example between 10 and 100 mb. Underpressure control means  60  can be placed in the vicinity of the end of line  14 , near extraction means  3 . These means can be a valve, a choke, or any other means allowing to vary the underpressure in the line and/or vessel  6 . The inside diameter of transport line  14  ranges between 5 and 15 mm, preferably about 10 mm. The material of the inner tube is selected to be impervious to hydrocarbons, such as for example fuel supply pipes. In order to prevent condensation of the gas conveyed, in certain extreme situations, it can be absolutely necessary to heat at least a portion of the wall, for example by means of a heating cord  23 . 
     Vessel  6  comprises a gas inlet  24  for an inert gas or air, controlled by a valve  25  allowing to adjust the gas inflow rate. This valve can be controlled by means of a line  26 . 
     In series on line  14 , sampling means  27  for the conveyed gas flow sample a certain amount of gas according to a rate depending notably on the measuring cycle. The sampler is controlled by line  28 . Sampling means  27  comprise: a loop referred to as &lt;&lt;chromatograph&gt;&gt; loop in which a volume of gas is taken from line  14 , valves or distributors for carrying out this sampling operation, then for driving this volume of gas by pushing it with an inert fluid. These various constituents are detailed more precisely by means of FIGS. 3 a  and  3   b . FIG. 1 diagrammatically shows injection line  29  for a carrier gas intended to displace the gas sample taken from line  14  by sampling means  27 , delivery line  30  intended to lead this volume of gas into analyzer  31 , for example a chromatography device. The measurements performed by means of device  31  are sent, by means of an electronic interface, to a central unit of a computer that processes these measurements in order to provide for example a record giving the nature and the amounts of the constituents carried along by the drilling fluid, according to the borehole depth. 
     At least a zone of sampling means  27  and a portion of line  30  can be heated by heating means  33  in order to prevent condensation before or during measurement. Means  34  for eliminating or at least decreasing the steam content of the circulating gas flow can furthermore be placed on this line  30 . 
     FIGS. 2 a  and  2   b  describe a conventional sampling valve  40  according to the prior art, which allows to better appreciate the considerable improvements provided by the present invention. In FIG. 2 a , line  41  communicates with an atmospheric degasser (not shown), the gases taken from the fluid being displaced in line  41  by means of an air circulation. Valve  42 , once closed or partially closed, diverts the effluent so that it flows through valve  40  through channels D and C, then into sampling loop  43  prior to flowing back through the valve through channels F and E and to rejoining main line  41 . Channel A is connected to a carrier gas (air, helium, hydrogen or nitrogen) supply. Channel B is connected to the chromatographic analyzer. FIG. 2 b  shows the circuit in analysis position. The position of the ball of valve  40  has been changed so that the carrier gas in A communicates with channel F to displace the effluent trapped in loop  43  towards the analyzer at B by passing through channel C. A bypass line of line  41  passes through channels D and E. The volume of gas sent into the analyzer is about some ten microlitres (10 −6  l) at a pressure very close to the atmospheric pressure. 
     FIG. 3 a  shows a sampling valve  50  that can be similar to valve  40  of the prior art. Line  51  is placed under underpressure since it is connected to a vacuum pump. A sampling loop  53  can be connected to the line and to valve  50  as in the prior art, but lines  55  and  54  furthermore communicate directly with partial vacuum line  51 . Controlled valves  56  and  57  open or close these communications. The volume of sampling loop  53  is much greater than that of the prior art since the volume of the effluent is low at absolute pressure. In the embodiment described here, the volume of loop  53  is about 1000 μl. In FIG. 3 a , valve  50  is in sampling position, the effluent sucked by the vacuum pump flows through loop  53  by means of direct bypass lines  55  and  54 , valves  56  and  57  being open. Valve  52  can be more or less closed, according to the pressure drop required. If need be, the bypass line passing through C, D, F and E is always in operation. Thus, by selecting a sufficient inside diameter for lines  55  and  54 , the high pressure drops in the valve, due to the partial vacuum required for the present invention, are minimized. FIG. 3 b  shows the circuits in analysis position. Valves  56  and  57  are closed, the sampling valve delivers the carrier gas from channel A to channel F so as to push the effluent contained in loop  53  towards the chromatographic analyzer at B. Preferably, valve  52  is sufficiently open so that the underpressure is not limited by the pressure drops in circuits D and E. The effluent contained in the loop is partly compressed by the carrier gas, which imposes control of the temperature in all these circuits, loops and valves, so as to prevent condensation of the constituents in the effluent. A heating system  58  maintains a sufficient temperature of about 200° C. for example. 
     In order to test the system according to the invention, the following measurements were performed on a model comprising a 100-m or 200-m line having an inside diameter of 10 mm. A valve intended for control of the incoming air flow is mounted on a first end of this line. Pressure Pe is measured at this end Pressure Ps is measured at the other end that is extended by a 5.7-m tube with an inside diameter of 6 mm, connected to a vacuum pump where pressure Pppe is also measured. 
     According to the air flow rate (measured at atmospheric pressure and at ambient temperature), the absolute pressure values are given in the table hereafter: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                     Flow rate 
                 Pppe 
                 Ps 
                 Pe − (L = 100 m) 
                 Pe − (L = 200 m) 
               
               
                 (ml/min) 
                 (mb) 
                 (mb) 
                 (mb) 
                 (mb) 
               
               
                   
               
             
             
               
                 200 
                 3 
                 19 
                 29 
                 38 
               
               
                 400 
                 4 
                 26 
                 42 
                 53 
               
               
                 600 
                 5 
                 34 
                 53 
                 65 
               
               
                 800 
                 6 
                 40 
                 62 
                 76 
               
               
                   
               
             
          
         
       
     
     It is clear that the system according to the invention allows to apply an absolute pressure of some ten millibars in the extraction means, which is generally sufficient for &lt;&lt;heavy&gt;&gt; C5-C8 hydrocarbons. It can be reminded here that the sampling loop of the present invention is designed and arranged on the transport line so as not to provide a noticeable pressure drop on the line. 
     The time of transit of the constituents should not exceed about 120 seconds for the system to be operational. In order to assess the transit time, a determined gaseous mixture is injected at one end of the line and the appearance of this mixture is detected with a mass spectrograph connected to the other end. The following values were obtained with a 100-m long and 10-mm diameter transport line: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                        Flow rate (atm.) 
                 Pe 
                 Pppe 
                 Transit time 
               
               
                   
                 (ml/min) 
                 (mb) 
                 (mb) 
                 (s) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 282 
                 36 
                 3.6 
                 56 
               
               
                   
                 197 
                 29 
                 3 
                 72 
               
               
                   
                 140 
                 25 
                 2.5 
                 85 
               
               
                   
                 86 
                 21 
                 1.9 
                 109 
               
               
                   
                 60 
                 17 
                 1.6 
                 142 
               
               
                   
                   
               
             
          
         
       
     
     These measurements allow to validate an operation optimization model that takes into account the volume of gas extracted, including the steam, according to the P and T conditions previling in the extraction means. If the volume of gas sucked is not sufficent to obtain an acceptable transit time, it is possible to either heat the fluid with electrode  8  (FIG. 1) in order to obtain more steam or to allow an additional gas by controlling the opening of valve  25  and the incoming flow. A quantification representative of the content of the constituents carried along by the drilling fluid is preferably obtained without any external gas supply through line  24  (FIG.  1 ). It is however possible to work with an external gas, air or nitrogen, supply insofar as calibration of the measuring system is possible. 
     The cnditions of extraction, transport and analysis of the C1-C8 constituents are variable and depend on the nature of the drilling fluid, on the nature of the formations crossed by borehole, on the rate of circulation of the drilling fluid, on the tamperature of the fluid and of the ambient air. The system according to the invention therefore affords the advantage of allowing a high adjustment flexibility, whether for the P and T conditions during extraction, the flow rate and pressure conditions for the transit time or the injection of a sample into the chromatographic analyzer. 
     In order to complete the tests carried out with the model described above, pressure and transit time measurements were performed with incorporation of the sampling loop as described above. The pressure drop dp is furthermore measured at the ends of valve  52  (FIG. 3 a , or  3   b ), i.e. at the ends of sampling loop  53  under the most unfavourable conditions, i.e. valves  56  and  57  closed. 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                     Flow rate 
                 Pe 
                 Ps 
                 Dp 
                 Pppe 
                 Transit time 
               
               
                 (Nml/min) 
                 (mb) 
                 (mb) 
                 (mb) 
                 (mb) 
                 (s) 
               
               
                   
               
             
             
               
                 140 
                 — 
                 — 
                  0 
                 — 
                  85* 
               
               
                 140 
                 27 
                 18 
                         8* 
                 1.9 
                 108 
               
               
                 140 
                 34 
                 28 
                 16 
                 1.9 
                 134 
               
               
                 140 
                 42 
                 37 
                 26 
                 1.8 
                 160 
               
               
                 140 
                 51 
                 47 
                 36 
                 1.8 
                 197 
               
               
                 140 
                 68 
                 65 
                 &gt;50  
                 1.8 
                 257 
               
               
                   
               
               
                 *measurements on the line without sampling loop, by way of comparison.  
               
             
          
         
       
     
     These measurements show the adjustments of the pressure drop created by valve  52  so that the sampling loop receives a flow diverted from the main line, without the flow rate/pressure equilibrium being disturbed upon each sampling. It has been checked that the samples taken are really representative of the effluent transported by the main line. It is clear that valve  52  can be pilot-controlled if need be.