Studies of Annular Gas Flow Following Primary Cementing

Abstract

Abstract Annular gas flow has been a problem in the Alberta oilfields for several years. Much of the evidence for annular flow can be found in abandoned wells in southeastern Alberta and various producing wells in the Slave Lake area. This paper will review in 'some detail specific examples of gas flow problems and a cement slurry and cementing technique which has been successful in arresting this problem. Much research has been done in the area of cement slurry phase behaviour and the effects that this phase behaviour has on downhole formations. Results of laboratory testing and field applications will be presented as well as an overview of cement behaviour after cementing. Annular Gas Flow Problems in Alberta The flow of annular gas occurs in many different areas in Alberta because of various conditions. The following are a few problem areas which exhibit this phenonemon and their specific circumstances. Medicine Hat Area-Southeast Alberta Several formations in this area have gas leakage problems after cementing and require attention. The Second White Gas flow problems have occurred in the Milk River and Medicine Hat formations of southeast Alberta for years. The most critical problems have occurred after setting open-hole abandonment pings in shallow gas wells. These plugs cover most of the Milk River Formation and extend into the surface casing. Gas leakage is noticed in many cases after cementing. If the gas leakage is severe enough, then remedial action is required, such as drilling out and resetting the abandonment plug over the Milk River Zone. Problems have also occurred where gas is leaking between production and surface casing after production casing is set. This requires several expensive remedial steps, such as perforating and squeezing, and extensive service rig time. Lloydminster Area-Northwest Alberta Several formations in this area have gas leakage problems after cementing and require attention. The Second White Specks Formation near the Lloydminster area is the most critical. Other formations of concern are the Colony and Wabiskaw around Lac La Biche. Both of these areas experience gas leakage after cementing and must be dealt with at great expense to the operator. Grande Prairie-Northwestern Alberta This area has also experienced gas migration and channeling after cementing. Some of the problem areas occur in the Mussreau and Kakwa area. Annular Gas- The Unwanted Product Annular gas migration can occur in wells where the gas escapes at the surface and can be monitored. It can also occur underground by migration from a gas zone to another zone of lower pressure. Both systems are wasteful, dangerous and costly to repair. The problem of annular gas is not new. For many years, operators accepted the fact by completing wells and then performing remedial cement squeezes prior to producing. During the 1960s, extensive laboratory and field research was begun in an attempt to control the complex problem. Large-scale laboratory model studies evaluate several different drilling fluids, spacers, flushes and cement slurries with density, viscosity, flow characteristics, fluid loss and pipe configurations as the main parameters.