A System For Continuous On-Site Measurement Of Sulfides In Water-Base Drilling Muds
Authors: Hadden David M. 
Published: December 2007

Abstract
The drilling of wells in areas where H2S may be present can lead to injury of personnel and damage to equipment if proper H2S personnel and damage to equipment if proper H2S protection measures are not taken. The protection measures are not taken. The ability to reliably measure certain parameters continuously and directly in the drilling mud can be an invaluable aid in a sulfides management program.
An in-mud monitoring technique is evaluated. Laboratory and field testing of the sensors and electronics circuitry are described.
The integrated system thus developed reads out three measurements: total soluble sulfides, H2S hazard potential, and mud pH.

Introduction
The possible existence of sulfides, particularly hydrogen sulfide, in drilling mud particularly hydrogen sulfide, in drilling mud poses a very serious threat to the safety of poses a very serious threat to the safety of drilling operations. Among the hazards involved are the extremely high toxicity of hydrogen sulfide, its ability to embrittle high-strength metals under certain conditions and the corrosiveness of sulfides in general. If proper precautions are not taken to warn against the appearance of sulfides encountered in drilling so that effective countermeasures can be taken, injury to personnel and damage to equipment can be catastrophic. Because of increasingly demanding drilling situations, coupled with stricter state and federal regulations regarding H2S concentrations around wells, rapid and accurate sulfide measurement and effective sulfide control in muds is more important now than ever before.
Up to now, however, no satisfactory system or instrument has existed for continuously analyzing and monitoring sulfide conditions directly in drilling mud. Several instruments are available which measure H2S in the air and at least two instruments are available which measure total soluble sulfides concentration in the mud, but not continuously. Clearly there is a need for a system which can continuously monitor the sulfide condition of muds so that potential hazards - such as the release of H2S - can be detected and warned against as early as possible. possible. It was thus our aim to develop such a system which could be used, for example, to signal developing sulfide problems in muds untreated for sulfides and to help determine the effectiveness of in-progress sulfides treatment programs.

THEORY AND DEFINITIONS
It was our premise that a successful sulfides management technique should be based on the measurement of three parameters:the total soluble sulfides concentration in the mudthe pH of the mudthe amount of H2S gas present in the air
It was decided to focus our attention on the problem of measuring the required parameters directly in the drilling mud using ion parameters directly in the drilling mud using ion selective electrodes (ISE's).

Measurement of Sulfur in water-Based Drilling Mud
The first task was to obtain an accurate measure of the total soluble sulfides in the mud. (We are not concerned here with the insoluble states of sulfur - elemental sulfur and heavy metal sulfide precipitates - as these pose no threats from the standpoint of toxicity or corrosion.) In soluble form, sulfur mostly exists in three states which are in equilibrium with one another:dissolved H2Shydrosulfide ion (HS-)sulfide ion (S—)