Thimm Engineering offers expertise in the engineering chemistry of SAGD, which is applicable to several aspects of performance optimisation.
Did you know the commonly used stain tube (Draeger tube) analysis could actually dramatically over-predict H2S production in SAGD?
Thimm Engineering has developed a new method of measuring hydrogen sulphide concentrations in gas streams, suitable for SAGD operations. This improved sampling method has been tested and refined in the field on operating SAGD projects. Its improved accuracy in H2S prediction can save both operating costs today and millions of dollars in future development costs by potentially eliminating the need for sulphur recovery.
The Thimm Engineering method has a standard error of about 5%. By contrast, the stain tube, or Draeger measurements commonly used for SAGD operations have been proven to be correct only within an order of magnitude.
Hydrogen sulphide measurement is usually performed by means of stain tubes in the field, because laboratory analysis of gas from a normal stainless steel gas cylinder will not give meaningful results.
This technique, while suitable for the natural gas industry, is problematic for SAGD because of the solubility of hydrogen sulphide in steam condensate at SAGD operating conditions. As a produced gas line or facility with a significant steam pressure is being sampled, the quality of the steam will change in the sampling line and in the stain tube itself. Hydrogen sulphide will re-partition into gas and liquid phases making accurate measurement via stain tube almost impossible.
The simplest method of alleviating the problems with stain tube methods is to force all steam to condense early in the train, regardless of quality, and chemically and quantitatively trap hydrogen sulphide in the same location in the train.
Schematic of Thimm Engineering Sampling Train for Hydrogen Sulphide Measurement
Steam is forced to condense in a Greenburg-Smith impinger commonly used for stack surveys. Hydrogen sulphide is trapped by copper sulphate solution to make copper sulphide,
Cu2+ + H2S → CuS + 2H+
The content of condensed water after the test is easily measured by weighing both the first impinger and the drying tube before and after the test. The solution containing the precipitated copper sulphide is then quantitatively recovered from the impinger in the field, and the copper sulphide separated in the laboratory. Chemical dissolution of the separated precipitate then permits analysis of the total amount of copper recovered, and calculation back to the amount of hydrogen sulphide trapped.
The dried non-condensable gas is measured by means of a dry test meter at the end of the train. Recombination calculations then permit the calculation of steam content, hydrogen sulphide concentration, and non-condensable gas content in the stream.
To learn more, contact Thimm Engineering or read the following papers:
Hydrogen Sulphide Measurements in SAGD Operations – Part I
Hydrogen Sulphide Measurements in SAGD Operations – Part II
Operation at low reservoir pressure in SAGD does more to lower the cost of your operations than just reducing Steam/Oil Ratio (SOR).
Thimm Engineering can provide expertise on how to capture the additional benefits of low pressure SAGD in the operation of your surface facilities.
Acid gases, carbon dioxide and hydrogen sulphide, are produced in SAGD projects by a process called “aquathermolysis”. Carbon dioxide is thought in part to originate from the bitumen, as a result of decarboxylation reactions, and in part from the sand.
Acid gas quality in SAGD will in almost every case be poor, resulting in challenges to sulphur recovery efficiency.
High steam pressures in SAGD operations tend to cause the dissolution of silica minerals in the steam zone, and result in their production with produced water. This can result in several problems including deposition is facilities and reaction with other components of the produced water to form unusual silicate scales. Some of these problems can be alleviated through operation at lower pressures.
Carbonate minerals such as calcite and dolomite tend to scale in facilities with higher temperature. The same scaling tendency is predicted for producing wells.
To learn more, contact Thimm Engineering or read the following papers:
Dependence of Some SAGD Operations Characteristics on Steam Zone Pressure