Abstract

Casing leak is one of the major reasons for wells to be worked over in oil fields. It has a negative impact on well production and might damage the productive zone depending on the leak severity, well completion configuration and well integrity. It is also detrimental to well hardware and safety. In the worst case scenario hydrocarbon reaches the surface causing an environmental spill and the well has to be plugged and abandoned. Most of the reported casing leaks occurred due to corrosion are the result of poor cement and long exposure to corrosive gases. Other reasons for casing leaks could be drill pipe wear, damaged casings owing to improper torque up practices, or wrong casing grade selection. The production wells are to be drilled and completed with the intent to pump hydrocarbons for the longest possible period of time before any work over (WO) is due. Casing leaks could occur in the course of drilling operations or after completion time. There are two types of casing leaks encountered during work over operations: two-way and one-way leaks (dumping or taking) depending on direction of flow, cement integrity and formation characteristics behind the casing. The first example is seen mostly across shallow aquifers that have sour gas and are difficult to cement due to incurable losses. The second example occurs across highly over pressurized corrosive water bearing zones that are tight and underlying, or overlying high permeable zones, making cementing the annulus difficult and causing potential leaks. The WO team has come up with an effective approach for each type of leak that is time saving and cost-effective, and provides a long lasting solution. Also, drilling and cementing practices in fields where casing leaks occur have been revisited to prolong the life of wells. This paper explains all types of leaks and their consequences. In addition, it highlights the circumstances that accompany casing leaks and provides an analysis tool for best casing leak repair approach based on a thorough in depth statistical study.

You can access this article if you purchase or spend a download.