Safe Handling Of H2S When Drill Stem Testing
Authors: Archibald Ralph G. 
Published: December 2007

Introduction

For many years drillstem testing has been the vehicle primarily used to determine the initial productivity of oil and gas primarily used to determine the initial productivity of oil and gas wells. All such wells are not of the "sweet" variety and many new discoveries in deeper formations contain varying percentages of lethal hydrogen sulfide gas. This paper intends to outline the inherent hazards associated with the drillstem testing of such wells.

With deeper formations being probed in the search for energy, hydrogen sulfide has been encountered both on- and offshore. One of the basic problems of this gas is its toxicity to man, corrosion attacks on metal, and its disrupting influence on drilling fluids. Drillstem testing at sweet oil and gas wells is just a normal operation on most drilling rigs. The picture changes very quickly when hydrogen sulfide is expected or encountered during a test.

DRILLSTEM TESTING

First, we must consider the safety of personnel at the rig site. Qualified safety people must be in attendance throughout the test. Normally a safety consulting company with breathing and resuscitation equipment will be hired on a per-day basis to handle the test. They normally supply drillpipe inhibitor and ammonia for hydrogen sulfide neutralizing. Some companies, including the drilling contractor, also will have their own safety representative in attendance, depending on availability. If sour gas is encountered, the safety consultant will continuously monitor the proceedings before and during the test and pulling of the pipe. proceedings before and during the test and pulling of the pipe. The sour gas contained in the drillpipe will be neutralized through the use of anhydrous ammonia mixed with equal parts of water poured down the pipe as the stands are broken off. The amount of ammonia used is dependent on the percentage of hydrogen sulfide. If a pump-out sub is used, which is normal nowadays, this procedure is pump-out sub is used, which is normal nowadays, this procedure is not required. When the tools below this sub reach the surface and are sour, crew members will mask up and break down the tool.

Should you have to pull a sour string of pipe for any given reason, the crew will have to mask up for the entire pull out of the hole. Floor men will use air-line work masks complete with egress or escape cylinder of air. The driller will use this also and an air-line unit will be strung to the derrick man. Other personnel required on the floor normally will use a back-pack unit. personnel required on the floor normally will use a back-pack unit. All other personnel will vacate the immediate area. The fewer people on the lease, the better. All air lines are supplied with people on the lease, the better. All air lines are supplied with breathing air from several 300 cu ft cylinders on the mobile safety unit, as well as oxygen resuscitation equipment.

During the test when pipe is being pulled, test plugs are employed to prevent fluid or gas from unloading as it is agitated. Several types of plugs are used, depending upon type of packer used. The inflatable packer does not allow pipe rotation; therefore, the derrick man must unscrew the plug at his position in the derrick. Packers that allow rotation permit the use of other style test plugs Packers that allow rotation permit the use of other style test plugs that dislodge as the pipe is rotated. In any event, be sure there are test plugs on the rig for drillstem tests. Occasionally the testing companies supply this equipment.

Other on-floor testing equipment supplied by the test company is the fail-safe remote-control head assembly and floor manifold. This whole assembly is normally pretested on site to 5,000 psi, or higher depending on area. These tools, including the test tools, will be magnafluxed prior to test for hydrogen sulfide embrittlement. The actual test tool will be hydrogen sulfide inhibited, inside and out, before going into the hole. All test pipe and flexible joints must be safety chained to prevent whipping pipe and flexible joints must be safety chained to prevent whipping around should they fracture during unexpected high pressures.

A small-diameter hose is attached to a high pressure valve on the floor manifold. As pressure builds up, the end of the hose is submerged in a nearby pail of water. Increasing bubbles indicate a possible gas or water flow into the pipe. This is used also to possible gas or water flow into the pipe. This is used also to test for hydrogen sulfide gas.