The Recommended Practice for Surface Casing Vent Flow and Gas Migration Intervention
- Harold Joseph Slater (PennWest Energy)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 19-22 September, Florence, Italy
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 6.5.1 Air Emissions, 1.11 Drilling Fluids and Materials, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6.11 Plugging and Abandonment, 1.6 Drilling Operations, 3 Production and Well Operations, 5.6.1 Open hole/cased hole log analysis, 2.2.2 Perforating, 6.5.7 Climate Change, 4.6 Natural Gas, 1.10 Drilling Equipment, 5.1.1 Exploration, Development, Structural Geology, 1.11.3 Drilling Fluid Management & Disposal, 4.1.2 Separation and Treating, 1.14 Casing and Cementing
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The migration of gas to surface by means of the production casing/openhole and the production/surface casing annulus is a common occurrence in the petroleum industry. There are also situations wherein migrating gases will negotiate a route to surface outside the surface casing.
The repair of these situations is a non-revenue generating exercise with the potential to reach significant expenditures. The recommended strategy will efficiently initiate and direct this process consequently minimizing the total cost of this intervention. The process commences with a logical technical approach to identify the gas source or sources that are responsible for the problem. The next step is to communicate with this gas source in a manner that enhances a remedial cementing activity. It concludes with the task of cement squeezing the source using a low rate cement squeeze technique to permanently seal the gas source thus preventing gas flow. This methodology has proven to be extremely successful and the subject paper describes in detail the recommended methods for identification, access to and sealing of the gas source responsible for these issues. Case histories will also be presented to illustrate strategies within the intervention.
Unwanted gas and/or liquid flows to surface either between the surface/production casing annulus or outside the surface casing are a serious liability in the development and production of oil and gas. Methane gas is an air pollutant and a global warming contributor. Also, if the useable water mechanisms are not protected with the surface casing installation, it is logical to assume that there is a potential to contaminate these waters. As well, a safety concern may exist depending on well location and nature of the vent flow. A good understanding of the geology penetrated by the wellbore is essential in order to assess all potential gas bearing reservoirs that may be contributing to the problem. In complex scenarios, there could be gas movement between adjacent wells due to primary cementing issues that permit uphole horizons to be invaded. Mature fields are vulnerable as the cementing practices during their development were inadequate. The industry is confronted with a significant challenge to understand and remediate these scenarios.
A permanent repair of these situations is difficult to accomplish and certainly more difficult if the intervention is initially addressed inappropriately. A gas flow is the most common, the repair of which will be the focus of this paper. The Alberta, Canada regulatory body has categorized surface casing vent flows to be either serious or non-serious in nature. A vent flow of gas and/or liquid is considered serious if (1) useable water zones are not covered by surface casing or the production casing primary cementing operations (2) the gas flow rate exceeds 300 cubic meters per day (3) the surface casing vent stabilized shut-in pressure is greater than 11 kilopascals per meter multiplied by the surface casing set depth (4) hydrogen sulfide is present (5) hydrocarbon liquid is present (6) non useable water is present which is any water with a total dissolved solids greater than 4000 milligrams per liter (7) the stabilized shut-in pressure of a useable water vent flow is greater than 11 kilopascals per meter multiplied by the surface casing set depth (8) the vent flow constitutes a fire, public safety or environment hazard. A serious vent flow must be repaired within 90 days of the detection date while a non-serious vent flow can be repaired at the time of well abandonment.
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