Surface Subsurface Safety Systems
Authors: Hargrove D.N. , Raulins G.M. 
Published: December 2007

In today's day and age of modern gas and oil production, it becomes increasingly necessary to have an adequate and reliable safety system. The reasons for a good safety system are numerous. Consider the nature of the fluid and gas itself, which is under pressure and extremely flammable. This necessitates a system which will protect the increasingly high capital investments in equipment and structures, protect the environment against ecological damages which could occur, prevent the unnecessary waste of our natural resources, and most important of all, protect the lives of individuals working in the area itself. An adequate safety system is one of the least expensive methods of ensuring all the above, as the most sophisticated safety systems usually cost less than one per cent of the total capital investment of a production system.

There have been several instances in the past where a good safety system has provided adequate production.A platform off the California coast upon which an explosion occurred. The monitoring system on the platform immediately sensed the explosion and activated the safety system, shutting in all wells at the mud line.In many hurricane situations off the Louisiana coast in the Gulf of Mexico, platforms have been damaged or destroyed. Uncontrolled production of wells was prevented by downhole safety equipment in some cases, and in other cases by surface safety equipment.In many instances, minor malfunctions of control equipment on platforms or in flow lines that could have caused damage to the platform systems, and perhaps wells, had the malfunction gone undetected, have been prevented by safety equipment on the platform that sensed the malfunction and shut in the wells.Many more cases could be cited wherein the combination of downhole and/or surface safety equipment has been utilized to detect malfunctions and to shut in gas or oil wells in order to prevent incalculable damage to the environment and loss of natural resources.

In contrast to what has just been mentioned (Fig. 1), there have been several instances where the absence of an adequate safety system has cost many lives, millions of dollars of property loss, severe ecological damage, loss of natural property loss, severe ecological damage, loss of natural resources, plus the huge investment necessary to re-establish well integrity.

In designing a safety system, it is necessary to decide what type and where protection is required, then match the equipment best suited to the situation.

Flowing land wells and certain artificially lifted wells near schools, churches, roads, villages, cities, and factories need a more automated shut-in system than those wells in a more remote area. However, even in remote areas the possibility of natural disasters should be taken into account, and the well and environment adequately protected. Also, flowlines and gathering lines which are subject to vehicular damage and which may pass through wildlife sanctuaries or over rivers and lakes should be included in an overall safety system. Areas where excessive heat or fire is possible, such as near heaters or separators, should have proper heat sensing devices.

Greater protection should be planned for costly offshore locations where escape is more difficult for personnel and where fire fighting is extremely costly in time, equipment, and loss of production.

In addition, the liability for damage to fishing waters, beaches, and shipping is rapidly increasing. It is necessary to provide automatic shut-in systems to protect against marine vessels that have to pass through most offshore fields. Not only may storm and wave action cause damage to production equipment, but also barges and other vessels set adrift by the storm may pound against the installation. On multi-well platforms, the tree could be damaged while moving a rig or platforms, the tree could be damaged while moving a rig or other equipment. Subsurface safety valves that are designed to automatically shut-in a well are essential. Other considerations are emergency shut-in devices on the helicopter deck, the rig floor, and other remote locations. Fully automatic shut-in protection for flowlines against damage and fire should also be considered.

Special considerations when designing a safety system that should not be overlooked are possible breaks to sales lines by increased pressure or plugging of lines, chokes cutting out, heater, treator or separator problems or fires, and even the possibility of sabotage.

In examining the operation of a safety system, let us look first at the equipment making up the surface safety system, then look at the equipment in the subsurface safety systems, and, finally, examine safety systems in which the surface and subsurface systems are combined to give a total integrated safety system.