Design and Fabrication of a Low Rate Metering Skid to Measure Internal Leak Rates of Pressurized Annuli for Determining Well Integrity Status

Abstract

Abstract In the oil industry, the wells are designed to have at least two tested barriers intact and maintained at all times to avoid any uncontrollable release of hydrocarbon/water at the surface. A sustained annulus pressure indicates failure of one or more well barriers. It is important to measure the leak rate associated with a barrier failure in order to properly risk assess the well from safety and operation integrity point of view. In case of a downhole barrier (completion, tubing, casing or cement) failure, surface pressure may be seen in the annuli. In such a case, the question of how to live with and how to manage these annuli pressures are always raised. The risk associated with this failure are defined considering annulus pressure value (Should not reach Maximum Allowable Annulus Surface Pressure (MAASP) which safeguard the weakest element in the pressure envelop) and leak rate of effluent fluids of the annulus. Annulus fluid leak rate provides a sense of the leak path geometry and the risk associated with the annulus pressure in case of loss of wellhead control. The company has defined Allowable Leak Rate for oil, gas and water as 6.3 gallon/hr, 15 SCF/min and 400 gallon/hr respectively as standards. In case of sustained annulus pressure with leak rate outside the acceptable range, an immediate action is required to secure the well, carry further investigations and plan proper well intervention to restore the annulus integrity. The leak rate measurement can be performed through test vessels but this will be good for the high flow rates. The test vessel costs more money and delays other routine operations. On the basis of these limitations, the idea came to design and fabricate a portable Meter Skid capable of measuring low flow rates especially for off shore operations. A portable fit for purpose Meter Skid to measure annulus fluids rate measurement has been fabricated by the company. The Skid is basically a small knock out drum comprises a drum with level glass, flow meter for gas and piping with gauges built on a skid with lifting hooks. During flow rate measurements, extra oil is decanted using a small portable pump. The Meter Skid is unique and one of its kind which helps to measure the small flow rates from the annuli to better define the well integrity status of the well in the light of company Well Integrity Standards.