ICP Prevention in Wells Controlling the Leak Integrity of Casing Wellhead Seals

By Alexander Ryakhovskiy, October 22, 2013

The following technology is ideal for various types of development wells with ultra-low intake capacity of interstring space <0.0083 m³/(h*MPa) or less than 2 m³ per day at 10 MPa. To be applied immediately after well completion and throughout the operating period, until the well abandonment.

The intercasing pressure (ICP) of the wellhead equipment indicates a fluid flow in the interstring space, thread joints of the strings or the wellhead equipment, which is unacceptable for any type of well. Russian Fire Safety Standard 08-624-03 renders such wells as technically defective, requiring ICP liquidation measures or, failing that – well abandonment.

A well is a complex technical structure that becomes only more expensive with the development of new construction technologies. In global practice of well operation, there is no effective system for monitoring the leak state for casing head pack-off, casing strings and its thread joints; also, there is no technology to maintain a constant leak-proof state of downhole equipment and interstring space. In this article, we try to conceptualize and map out the comparatively low-cost technology that enables the producer to implement such controls for constant maintenance and monitoring of the tightness of downhole equipment and interstring space. This should significantly increase the operating life of wells, reduce labor and material costs for their repair and ensure better environmental security.

In this technology, ICP prevention and leak control for casing strings and interstring environment is realized by applying constant pressure in interstring space (ISS), direct injection into the ISS (to specified pressure) of special sealing liquid that seals the ISS migration channels and microgaps in thread joints of the strings. Then a flow meter can be used to gauge the ISS injection capacity, thus getting the data about the well integrity state. Regardless of ICP presence in the operational well, this preventive application of pressure to the ISS, together with a computerized control system for casing head pack-off, enables the operator to constantly monitor the leaks, the «health» of the well, preventing intercasing pressure during the operation and ensuring technical, technological and environmental safety of the operating wells.

This technology is based on the analysis of the causes of the ICP in the wellhead equipment.

ICP causes can be divided into three components:

1. Leakage of thread joints of the strings.

2. Leakage of casing head pack-off.

3. Leakage of the inhomogeneous ISS medium, used by formation fluids (mostly methane, as the most permeable gas) for migrating up and down via the micropores formed by the ongoing physical and chemical processes due to the violation of the natural balance in the formation during the construction of the well.

1. Leakage of thread joints in casing strings depends on the quality of the casing, its thread joints, quality of the string landing. During the operation of the well, casing strings are subject to mechanical, thermal, physical and chemical exposure. This results in micromovement of casing strings, both length- and diameter-wise [4], while constant vibration field (due to the movement of gas-liquid