On the Production of Hydrogen Sulfide-Sulfur Mixtures from Deep Formations

Abstract

Introduction The production of sour gases with high hydrogen sulfide is highly toxic and can cause failure in certain material. Additional difficulties may arise if elemental sulfur is present. Depending on pressure and temperature, this sulfur may precipitate from the solution, causing serious plugging of the formation, tubing and surface equipment. This paper concerns the flow of hydrogen sulfide accompanied by sulfur deposition in porous media. Pressure distribution and porosity reduction due to Pressure distribution and porosity reduction due to the precipitation and sulfur in the formation are simulated for a reservoir resembling that found recently in the Smackover formation in southern Mississippi. The effects of production rate, wellbore radius, and well spacing on the pressure history and on the accumulation of sulfur at the well face are investigated. A scheme for producing this type of fluid from deep formations is also suggested in this study. Mechanisms of Sulfur Deposition The problem of sulfur deposition associated with the production of sour gas has long been recognized. An production of sour gas has long been recognized. An earlier work proposed a mathematical model to describe the precipitation of a solid phase and its effects on fluid flow in porous media. In that study, cases were considered in which the reservoir fluid is saturated with elemental sulfur at its initial condition and some of the dissolved sulfur precipitates from the solution as a result of a reduction in solubility with a decline in pressure. The model is predicted a rapid buildup of solid sulfur in the vicinity of the well and insignificant accumulations near the other boundary of the reservoir. It was concluded that the tendency toward plugging by deposited sulfur at the well face can be reduced either by reducing the production rate or by choosing close well spacing. Unfortunately, both these methods would have adverse effects on the economics of the system since the former method increases the time needed to achieve a certain cumulative production and the later requires the drilling of more wells for a given sectional area. A better means of combating the plugging problem might be to create a large effective wellbore radius if the formation can be fractured. The advantage of such an approach will be discussed later. Concerning field operations of sour gas production, Hyne reported results of a 1967 survey of more than 100 producing wells in Canada and Europe. Of 31 cases tubulated, depositional of sulfur in tubing was observed in nine. The bottom-hole and wellhead pressures and temperatures of these nine cases are pressures and temperatures of these nine cases are plotted in Fig. 1. The content of hydrogen sulfide plotted in Fig. 1. The content of hydrogen sulfide varies from 5 to 54 percent in these fields. Although a complete survey of operations of sour gas production in the U.S. is not available a few cases have been reported in the literature. During drilling into Smackover formations in South Texas, a deep reservoir containing 98 percent H2S was discovered. JPT p. 1142