Method and relative system for the detection and quantification of the H2S in drilling mud

Abstract

Method for the detection and quantification of the H.sub.2S which measures concentration of the H.sub.2S in the drilling mud including the steps of measurement of the initial concentrations of H.sub.2S in free form and of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species, dissolved in the sample of mud; acidification of the sample of mud, to generate gaseous H.sub.2S, making the hydrogen sulphide (HS.sup.) and sulphide (S.sup.2) ions dissolved in the mud and the H.sub.2S precipitated in solid form in the scavengers react; measuring concentration of the gaseous H.sub.2S formed following the first acidification; and relative system including at least: a mud sample collector; a unit measuring concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species in the sample; a unit for measuring concentration of the free H.sub.2S; a unit to acidify the sample of mud; electronic controller and storage and processing of the measurements made.

Claims

1. A method for detection and quantification of hydrosulphuric acid H.sub.2S in a drilling mud, comprising the following steps: taking a sample of drilling mud placing said sample of mud in a sampling chamber; measurement of a concentration of gaseous H.sub.2S in free form present in a head space of the sampling chamber; measurement of a concentration of hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species, dissolved in said sample of mud; and acidification of said sample of mud, wherein after said step of acidification, the following steps are carried out: repetition of a cycle of steps that include taking of a gaseous sample from the head space of the sampling chamber, measuring a concentration of free H.sub.2S in said gaseous sample, said free H.sub.2S being generated following said acidification, and returning said gaseous sample to said sampling chamber, said repetition being performed until the measurement of the concentration of the free H.sub.2S in said gaseous sample does not vary with respect to the measurement of the concentration of the free H.sub.2S in said gaseous sample, performed in a previous cycle; and conversion of the measurement of the concentration of the free H.sub.2S in said gaseous sample into a measurement of concentration of the H.sub.2S in the mud.

2. The method according to claim 1, wherein said method further comprises, after said measurement of the concentration of gaseous H.sub.2S in free form present in the head space of the sampling chamber and before said step of acidification, the following steps: mechanical stirring of said sample of mud; and measurement of the concentration of free H.sub.2S, in the head space of sampling chamber, wherein said measured H.sub.2S is H.sub.2S freed following said stirring.

3. The method according to claim 2, wherein said method further comprises, after said repetition of a cycle of steps, a second acidification of the sample of mud, and after said second acidification, a second repetition of said cycle of steps.

4. The method according to claim 3, wherein said method further comprises a step of measurement of temperature in said sample of mud in the sampling chamber.

5. The method according to claim 2, wherein said method further comprises, before said repetition of a cycle of steps, a second acidification of the sample of mud.

6. The method according to claim 2, wherein said method further comprises a step of measurement of temperature in said sample of mud in the sampling chamber.

7. The method according to claim 2, wherein said method further comprises, after said step of acidification and before said repetition of a cycle of steps, a second mechanical stirring of said sample of mud.

8. The method according to claim 7, wherein said method further comprises a step of measurement of temperature in said sample of mud in the sampling chamber.

9. The method according to claim 7, wherein said method further comprises, before said repetition of a cycle of steps, a second acidification of the sample of mud.

10. The method according to claim 9, wherein said method further comprises, after said second acidification, a third mechanical stirring of said sample of mud.

11. The method according to claim 9, wherein said method further comprises a step of measurement of temperature in said sample of mud in the sampling chamber.

12. The method according to claim 1, wherein said method further comprises a step of measurement of temperature in said sample of mud in the sampling chamber.

13. The method according to claim 1, wherein said method further comprises a step of measurement of electrical conductivity in said sample of mud in the sampling chamber.

14. The method according to claim 1, wherein said method further comprises, before said repetition of a cycle of steps, a second acidification of the sample of mud.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following description refers to the accompanying drawings, in which:

(2) FIG. 1 is a diagram showing the system which implements the method which is the object of the present invention.

(3) FIG. 2 is a simplified representation of a detail of a first embodiment of the system of the present invention, relating to the sampling cell of the system, wherein said sampling cell is thermostat controlled;

(4) FIG. 3 is a simplified representation of a detail of a second embodiment of the system of the present invention, relating to the sampling cell of the system, wherein said means for the measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species (2, 3) in said mud sample (17) comprise means for the measurement of the temperature (18, 18, 28) in said sample of mud (17), said means (18, 18, 28) being integrated with said means for the measurement of the concentrations of the HS.sup. and S.sup.2 ion species (2, 3);

(5) FIG. 4 is a simplified representation of a detail of a third embodiment of the system of the present invention, relating to the sampling cell of the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) Referring to FIGS. 2, 3 and 4, a first embodiment of the method of the present invention provides for the following steps: taking of a sample of drilling mud (17); placing of said sample of mud (17) in a sampling chamber (1); measurement of the concentration of gaseous H.sub.2S in free form present in the head space of the sampling chamber; measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species, dissolved in said sample of mud; first mechanical stirring of said sample of mud; measurement of the concentration of gaseous H.sub.2S in free form, said H.sub.2S being freed following said first stirring; first acidification of the sample of mud, said first acidification being apt to make the hydrogen sulphide (HS.sup.) and sulphide (S.sup.2) ions dissolved in the mud and the H.sub.2S precipitated in solid form in the scavengers react, thus generating gaseous H.sub.2S; second mechanical stirring of said sample of mud; repetition of a cycle of steps comprising: taking of a gaseous sample; measurement of the concentration of free H.sub.2S in said gaseous sample, said free H.sub.2S being generated following said first acidification; and returning of said gaseous sample in the sampling chamber (1); said repetition being performed until the measurement of the concentration of the free H.sub.2S in said gaseous sample does not vary with respect to the measurement of the concentration of the free H.sub.2S in said gaseous sample, performed in the previous cycle; conversion of the measurement of the volumetric concentration of the H.sub.2S in the gaseous sample into a measurement of volumetric concentration of the H.sub.2S in the mud.

(7) Referring to FIGS. 2, 3 and 4, a second embodiment of the method of the present invention provides for the following steps: taking of a sample of drilling mud (17); placing of said sample of mud (17) in a sampling chamber (1); measurement of the concentration of gaseous H.sub.2S in free form present in the head space of the sampling chamber; measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species, dissolved in said sample of mud; first mechanical stirring of said sample of mud; measurement of the concentration of the gaseous H.sub.2S in free form, said H.sub.2S freed following said first stirring; first acidification of the sample of mud, said first acidification being apt to make the hydrogen sulphide (HS.sup.) and sulphide (S.sup.2) ions dissolved in the mud and the H.sub.2S precipitated in solid form in the scavengers react, thus generating gaseous H.sub.2S; second mechanical stirring of said sample of mud; repetition of a cycle of steps comprising: taking of a gaseous sample; measurement of the concentration of free H.sub.2S in said gaseous sample, said free H.sub.2S being generated following said first acidification; and returning of said gaseous sample in the sampling chamber (1); said repetition being performed until the measurement of the concentration of the free H.sub.2S in said gaseous sample does not vary with respect to the measurement of the concentration of the free H.sub.2S in said gaseous sample, performed in the previous cycle; second acidification of the sample, said second acidification being apt to make a possible residual quantity of HS.sup. and S.sup.2) ions dissolved in the mud and a possible residual quantity of H.sub.2S precipitated in solid form react, thus freeing, further, gaseous H.sub.2S; third mechanical stirring of said sample of mud; repetition of a cycle of steps comprising: taking of a gaseous sample; measurement of the concentration of free H.sub.2S in said gaseous sample, said free H.sub.2S being generated following said first acidification; and returning of said gaseous sample in the sampling chamber (1); said repetition being performed until the measurement of the concentration of the free H.sub.2S in said gaseous sample does not vary with respect to the measurement of the concentration of the free H.sub.2S in said gaseous sample, performed in the previous cycle; conversion of the measurement of the volumetric concentration of the H.sub.2S in the gaseous sample into a measurement of volumetric concentration of the H.sub.2S in the mud.

(8) Referring to FIGS. 2, 3 and 4, a third embodiment of the method of the present invention provides for the following steps: taking of a sample of drilling mud (17); placing of said sample of mud (17) in a sampling chamber (1); measurement of the concentration of gaseous H.sub.2S in free form present in the head space of the sampling chamber; measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species, dissolved in said sample of mud; first mechanical stirring of said sample of mud; measurement of the concentration of the gaseous H.sub.2S in free form, said H.sub.2S being freed following said first stirring; first acidification of the sample of mud, said first acidification being apt to make the hydrogen sulphide (HS.sup.) and sulphide (S.sup.2) ions dissolved in the mud and the H.sub.2S precipitated in solid form in the scavengers react, thus generating gaseous H.sub.2S; second mechanical stirring of said sample of mud; taking of a gaseous sample; measurement of the concentration of free H.sub.2S in said gaseous sample, said free H.sub.2S being generated following said first acidification; second acidification of the sample, said second acidification being apt to make a possible residual quantity of HS.sup.and S.sup.2) ions dissolved in the mud and a possible residual quantity of H.sub.2S precipitated in solid form react, further freeing gaseous H.sub.2S; third mechanical stirring of said sample of mud; repetition of a cycle of steps comprising: taking of a gaseous sample; measurement of the concentration of free H.sub.2S in said gaseous sample, said free H.sub.2S being generated following said second acidification; and returning of said gaseous sample in the sampling chamber (1); said repetition being performed until the measurement of the concentration of the free H.sub.2S in said gaseous sample does not vary with respect to the measurement of the concentration of the free H.sub.2S in said gaseous sample, performed in the previous cycle; conversion of the measurement of the volumetric concentration of the H.sub.2S in the gaseous sample into a measurement of volumetric concentration of the H.sub.2S in the mud.

(9) Should for the measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species use not be made either of a thermostat-controlled container for the collection of the mud sample or means for the measurement of the concentration of the ions able to perform automatic compensation for possible temperature variations, the method of the present invention will also provide a step of postprocessing subsequently the measurements of concentration of the HS.sup. and S.sup.2 ion species, said step of postprocessing consisting of the compensation of the measurements of concentration on the basis of the measurement of the temperature.

(10) The method of the present invention can further provide a step of measurement of the electrical conductivity of the solution made up of the sample of mud. Said step of measurement of the electrical conductivity is aimed at the control of the measurements of concentration of the HS.sup. and S.sup.2 ion species. As will be further explained here below, with reference to the system which implements the method of the present invention, the concentrations of the HS.sup. and S.sup.2 species are measured by measuring the variations of the potential of two electrochimicalcells from the prior art. The first one for the hydrogen ions H.sup.+ and the second one for the sulphide ions S.sup.2 Since it is known that the variations in the cell potential, supposing the temperature to be constant, can be said to be due exclusively to the variations in concentration of the ion species only if the ionic force is also constant, it is necessary to check that this condition is respected or that a compensation is performed for possible variations in said force. Since the ionic force can be estimated by measuring the electrical conductivity of a solution, monitoring said conductivity, the measurements of concentration can be compensated and thus a correct estimate obtained of the real concentration of HS.sup. and S.sup.2 ions.

(11) Referring to FIGS. 1, 2, 3 and 4, the system of the present invention, which allows implementation of the method described above, comprises: means for the collection (1) of a sample of mud (17); means for the measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species (2, 3), in said sample of mud (17); means for measuring the concentration of the free H.sub.2S (4, 5, 6, 7, 8, 9); means for the acidification (11, 12, 13, 14, 15) of said sample of mud (17); electronic means of control (19, 20) of said means for the measuring of the concentration of the free H.sub.2S (4, 5, 6, 7, 8, 9); electronic means of control (21, 22) of said means for the acidification (11, 12, 13, 14, 15) of said sample of mud (17); means of electrical supply (23) of said means for the acidification (11, 12, 13, 14, 15) and of said means for the measuring of the concentration of the free H.sub.2S (4, 5, 6, 7, 8, 9), as well as of said electronic means of control (19, 20, 21, 22) of said means for the measuring of the concentration of the free H.sub.2S (4, 5, 6, 7, 8, 9) and of said means for the acidification (11, 12, 13, 14, 15); means for the storage and processing (23, 24) of the measurements made by said means for the measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species (2, 3) in said sample of mud (17);

(12) Said means for the collection (1) of a sample of mud comprise a sampling chamber (1);

(13) Said means for measuring the concentration of the free H.sub.2S (4, 5, 6, 7, 8, 9) comprise: a flow chamber (4); a first pump (5) apt to the taking of a gaseous sample from said sampling chamber (1) and apt to the sending of said gaseous sample to said flow chamber (4); pipes (6) for the transfer of the gaseous sample from said sampling chamber (1) to said first pump (5); pipes (7) for the transfer of said gaseous sample from said first pump (5) to said flow chamber (4); pipes (8) for the transfer of said gaseous sample from said flow chamber (4) to said sampling chamber (1); and an electrochemical sensor (9) for measuring the concentration of the H.sub.2S in said gaseous sample contained in said flow chamber (4), said gaseous sample having been taken from said sampling chamber (1) and sent to said flow chamber (4) by means of said first pump (5).

(14) Said first pump (5), said flow chamber (4) and said sampling chamber (1) form a so-called sampling cell (10).

(15) Said means for the acidification (11, 12, 13, 14, 15) of said sample of mud (17) comprise: a strong acid (11), preferably hydrochloric acid HCl; a container (12) for the collection of said strong acid; a second pump (13) apt to the taking of said strong acid (11) from said container (12) for the collection of said strong acid (11) and apt to the sending of said strong acid (11) to said sampling chamber (1); pipes (14) for the transfer of said strong acid (11) from said container (12) for the collection of said strong acid (11) to said second pump (13); and pipes (15) for the transfer of said strong acid (11) from said second pump (13) to said sampling chamber (1).

(16) The system of the present invention can moreover comprise also: mechanical means (16) for the facilitation of the freeing of gaseous H.sub.2S from said sample of mud. Said mechanical means (16) for the facilitation of the freeing of gaseous H.sub.2S from said sample of mud (17) comprise, in turn, a magnetic stirring bar (16) placed inside said sampling chamber (1).

(17) In a first embodiment of the system of the present invention, which does not necessarily implement the first embodiment of the method of the present invention but can be used to implement the first, the second and the third embodiments of the method of the present invention, said sampling chamber (1) is a thermostat-controlled cell, i.e. able to maintain in its interior a constant temperature.

(18) Referring to FIG. 2, in a second embodiment of the system of the present invention, which does not necessarily implement the second embodiment of the method of the present invention, but can be used to implement the first, the second and the third embodiments of the method of the present invention, said means for the measurement of the concentration of the hydrogen sulphide HS.sup. and sulphide S.sup.2 ion species (2, 3) in said sample of mud (17) comprise means for the measurement of the temperature (18, 18, 28) in said sample of mud (17), said means (18, 18, 28) being integrated with said means for the measurement of the concentrations of the HS.sup. and S.sup.2 ion species (2, 3). More particularly said means for the measurement of the concentrations of the HS.sup. and S.sup.2 ion species (2, 3) are provided with an electrochemical sensor and with a sensor (18, 18) for the measurement of the temperature, known in the art as internal temperature compensation sensor.

(19) Referring to FIG. 3, in a third embodiment of the system of the present invention, which does not necessarily implement the third embodiment of the method of the present invention, but can be used to implement the first, the second and the third embodiments of the method of the present invention, said system comprises means for the measurement of the temperature (18, 18, 28) in said sample of mud (17), said means (18, 18, 28) being separate from said means for the measurement of the concentrations of the HS.sup. and S.sup.2 ion species In this case the system will also comprise a probe (28) for the measuring of the temperature, separate from the means (2, 3) for the measurement of the ion species, and means for the storage and processing (25) of the measurements taken by said probe (28) for the measuring of the temperature, said means for the postprocessing (25) being apt to perform subsequently the compensation of the measurement of the concentration of HS.sup. and S.sup.2 species for the temperature variations.

(20) Referring to FIGS. 2, 3 and 4, the system of the present invention may also comprise, in all three of its embodiments, means for the measurement of the electrical conductivity (26) in the sample of mud (17).

(21) In this case the system will also comprise means for the storage and processing (27) of the measurements made by said means for the measurement of electrical conductivity (26), said means for the processing (27) being apt to perform the compensation of the measurement of the concentration of the HS.sup. and S.sup.2 species for the electrical conductivity. In FIGS. 2, 3 and 4 said means for the measurement of electrical conductivity (26) are represented with a dotted line, to show that these are optional means.

(22) The invention described above achieves the objects set, overcoming the disadvantages of the prior art.

(23) The present invention provides in fact a system which allows the obtaining of measurements relating to the H.sub.2S in a controlled environment and at the same time, thanks to the presence of the sampling cell, offers the possibility of repeating several times, and continuously, the measurements of the H.sub.2S in a same sample of mud. This factor, together with the presence of a double acidification, means that a control can be carried out on the effective freeing in gaseous form of all the H.sub.2S present in the mud, whether dissolved in ionic form in the fluid part of the mud or precipitated in solid form in the scavengers. Finally, thanks to the measurement of the electrical conductivity in the sample of mud, it is possible to perform the compensation of the measurements of concentration for the variation in ionic force and thus obtain reliable estimates of the concentrations of the ion species derived from the dissociation of the H.sub.2S in the drilling mud.